Power Management Single-Cell Li-Ion Devices POWER MANAGEMENT Feat

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Power Management Single-Cell Li-Ion Devices POWER MANAGEMENT Feat

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SC908
Power Management Single-Cell Li-Ion Devices
POWER MANAGEMENT Features
Single Cell Li-Ion battery charger CC/CV charging with current soft start Charger regulated output voltage 4.2V over temperature with Kelvin sense battery voltage Charger input protection withstands indefinitely Charger constant current setting 500mA Adjustable charge termination current down 10mA Battery interface disables charging battery temperature range Programmable battery detector threshold Four status indicators Programmable charge completion timer Buck converter with enable output programmable from 150mA output Buck converter efficiency 50mA General purpose noise regulator with fast enable, active shutdown 4x4x0.9 (mm) MLPQ package WEEE RoHS compliant
Description
SC908 complete power management system designed Bluetooth wireless headsets, portable media players, other battery-powered electronics where size critical. Included full featured standalone Li-Ion battery charger with programmable low-battery monitor, noise regulator, DCDC buck converter. Battery charging features include programmable precharge, fast-charge, termination current settings. Charge termination controlled programmable timer resistor that sets termination current. input voltage protects against hotplug overshoot faulty adapters without additional protection circuitry. battery voltage Kelvin sense input eliminates errors high charging currents. battery thermistor interface disables charging when battery temperature exceeds safe-to-charge limits. step-down switching regulator (buck converter) improves system efficiency extends battery life. regulator powered directly from battery from buck converter output when efficiency critical. fast-starting noise regulator suitable audio, general purpose regulation required peripheral devices, such vibrating alert motor. battery detector warns when battery level below 3.3V, when battery discharged below lower programmable voltage limit.
Applications
Bluetooth headsets players cost mobile phones
Typical Application Circuit
Charging Adapter CVAD CVSYS RNPU Charging RNTC (Battery Pack Thermistor)
VSYS
BSEN RTIME
RRTIME RITERM CBAT
Li-Ion BATTERY
ITERM
RIPRGM
IPRGM EN_NTC
SC908
CHRGB FLTB LBATB RLBAT VREF AGND DGND
LVIN
supply from battery from DC-DC converter CLVIN
Audio Circuits vibrator motor
Charger Present
LVOUT
CSFB
SVOUT, Bluetooth Processor
CLVOUT
CSVOUT
RRLBAT
CVREF
PGND
CSFG
Patent: 6,836,095 January 2008 2008 Semtech Corporation
SC908
Configuration
EN_NTC CHRGB PGND
Ordering Information
Device Package
MLPQ-24 Evaluation Board
BSEN
SC908MLTRT(1,2) SC908EVB
VSYS IPRGM ITERM RTIME RLBAT
LBATB FLTB
Notes: Available tape reel only. reel contains 3,000 devices. Lead-free package only. Device WEEE RoHS compliant.
VIEW
LVOUT
VREF
AGND
LVIN
MLP-24; 4x4, LEAD 29°C/W
Marking Information
SC908 yyww xxxxx xxxxx
year manufacture week manufacture xxxx number
DGND
SC908
Absolute Maximum Ratings(1)
-0.3 +28.0 BAT, VSYS, CHRGB, FLTB, LBATB -0.3 +5.5 -0.3
Recommended Operating Conditions
Ambient Temperature Range (°C) Charger Input Voltage Range 4.45 7.05 Regulator Input Voltage Range VBAT Switching Regulator Input Voltage VBAT
SLX, LVIN, LEN, VBAT LVOUT VLVIN AGND -0.3 +0.3 PGND -1.0 +0.3 Voltage Other Pins -0.3 +6.5 Output Current Short Circuit Duration .Continuous DC-DC Converter Output Current (mA)(3) -265, +180 DC-DC Converter Output Current (mA)(4) ±600 Total Power Dissipation Protection Level (kV)
Thermal Information
Thermal Resistance, Junction Ambient (°C/W)(6) Junction Temperature Range (°C) .-40 +150 Storage Temperature Range (°C) +150 Reflow Temperature (°C) +260
Exceeding above specifications result permanent damage device device malfunction. Operation outside parameters specified Electrical Characteristics section recommended. NOTES: absolute maximum ratings with respect DGND unless otherwise noted. VSRC larger VBAT VVSYS Continuous Peak Tested according JEDEC standard JESD22-A114-B. Calculated from package still air, mounted (in), layer with thermal vias under exposed JESD51 standards.
Electrical Characteristics
Test Conditions: VVAD 4.75V 5.25 VBAT 3.7V; VLEN VVAD; values 25°C; -40°C 85°C, unless specified.
Parameter
Charger
Symbol
Conditions
Units
VADOP(1) VADUVLO-R VADUVLO-F Input Voltage VADUVLO-H VADOVP-R VADOVP-F VADOVP-H Battery Leakage Current lleakBAT
Operating Voltage UVLO Rising Threshold UVLO Falling Threshold UVLO Hysteresis (VADUVLO-R VADUVLO-F) Rising Threshold Falling Threshold Hysteresis (VADOVP-R VADOVP-F) VVAD=VSEN=VLEN=0V, VBAT=4.2V
4.45 4.05
4.25
7.05 4.45
7.05
7.80
SC908
Electrical Characteristics (continued)
Parameter
Charger (continued) Charging Adapter Operating Current VADICCQ VEN_NTC VVSYS, ICPB ICHRGB IFLTB ILBATB IITERM IIPRGM 0mA, VSEN VLEN Measured BSEN 20mA IBAT 500mA 125°C Measured BSEN VBSEN VVAD IVSYS 4.16
Symbol
Conditions
Units
Regulation Voltage
4.24
Precharge Threshold (Rising) Recharge Threshold (Falling) VSYS output voltage VSYS output current ITERM Programming Resistor IBAT Pre-Charge Current IBAT Termination Current IPRGM Programming Resistor IBAT Fast-Charge Current Dropout Voltage IPRGM Regulated Voltage ITERM Regulated Voltage RTIME Regulated Voltage
VTPreQ VTReQ VVSYS IVSYS RITERM IPreQ ITERM RIPRGM VIPRGM VITERM VRTIME tPreQF
Nominal 1%-tol Standard Value RITERM 4.99k RITERM 4.99k Nominal 1%-tol Standard Value RIPRGM 6.04k, VBAT 3.7V IBAT 500mA, 85°C RIPRGM 6.04k RITERM 4.99k RRTIME 37.4k RRTIME 37.4k 1.45 1.45 1.475 2.50 2.10 27.5 1.56 3.10 2.67 2.67 2.15 17.4 15.0 1.55 1.55 1.625 3.70 3.50 11.5 31.5 76.5
mins mins %VVSYS %VVSYS %VVSYS
Precharge Fault Time-Out
RRTIME connected VSYS RRTIME 37.4k Charge Complete Time-Out tQComp RRTIME connected VSYS VTNTC_DIS EN_NTC Thresholds VTNTC_HF VTNTC_CR EN_NTC Hysteresis EN_NTC Disable/Reset Hold Time Charger Over-Temperature Shutdown Temperature (Rising) VTNTC_HYS tNTC_DIS_H TCHRGR_OT Charger Disable/Reset (Falling) (Falling) Cold (Rising) VVAD Momentary disable resets charger
Hysteresis 10°C typical
SC908
Electrical Characteristics (continued)
Parameter
Core Functions (Excluding Charger) Core Circuits Quiescent Current VREF Reference Voltage VREF Power Supply Rejection IQ-Core VVREF PSRRREF VBAT 3.7V with 0.5VP-to-P ripple, 10kHz, CVREF 10nF Delay from first high high, VBAT 3.7V CVREF 10nF VREF from final VVAD VSEN VLEN VBAT 4.2V 0.75
Symbol
Conditions
Units
VREF Reference Voltage Start-Up Time
tSU_REF
DC-DC Buck Converter Buck Converter Input Voltage Buck Converter Under-Voltage Lockout Rising Threshold Buck Converter Under-Voltage Lockout Falling Threshold Buck Converter Under-Voltage Lockout Hysteresis Buck Converter Quiescent Current Buck Converter Minimum On-Time Buck Converter Maximum Duty Cycle (10) Buck Converter Program Output Voltage Minimum (6,10) Buck Converter Program Output Voltage Maximum(6,7,8,10) Buck Converter Feedback Regulation Voltage VSVIN VTSUVLO-R VTSUVLO-F VTSUVLO-HYS IBAT-Q tSON_MIN SDCMAX VSVOUT_MIN VSVOUT_MAX VSFB VBAT 3.7V, 4.7H ISVOUT 100mA 340k, 100k Buck Converter Line Regulation(6) VSVOUT_LINE 2.8V VBAT 4.5V ISVOUT 100mA 340k, 100k ISVOUT 150mA VSVOUT_LOAD VBAT 3.7V 340k, 100k 0.002 %/mA -0.3 VBAT VSVOUT_MAX/SDCMAX+150mV VSEN VBAT, ISVOUT 10mA mode PSAVE 2.55 also switching regulator supply input VBAT
0.480
0.500
0.520
Buck Converter Output Voltage(6)
VSVOUT
Buck Converter Load Regulation
SC908
Electrical Characteristics (continued)
Parameter
DC-DC Buck Converter (continued) Buck Converter P-Channel Peak Current Limit Buck Converter P-Channel On-Resistance Buck Converter N-channel On-Resistance Buck Converter Oscillator Frequency ILIM_P RDS(ON)P RDS(ON)N fOSC ISVOUT 150mA, VSVOUT VSVOUT VSVOUT 1.8V VSVOUT 2.2V VSVOUT 3.0V ISVOUT 150mA ISVOUT 150mA 0.85
Symbol
Conditions
Units
0.75
1.05
1.00
1.15
Buck Converter Start-Up Time (5,10)
tSU-SVOUT
1.45
Linear Drop-Out (LDO) Regulator Input Voltage Under Voltage Lockout Rising Threshold Under Voltage Lockout Falling Threshold Under Voltage Lockout Hysteresis Nominal Output Voltage Minimum (10) Nominal Output Voltage Maximum (10) Feedback Regulation Voltage Output Voltage VLVIN VTLUVLO-R VTLUVLO-F VTLUVLO-HYS VLVOUT_MIN VLOUT_MAX VLFB VLVOUT VLVIN VLVOUT +300mV VLVIN VLVOUT +300mV VLVIN 3.7V, ILVOUT 54.9k, 39.2k VLVIN 3.7V, ILVOUT VLVOUT 2.2V, ILVOUT 100mA Dropout Voltage VL_DO VLVOUT 3.0V, ILVOUT 150mA 54.9k, 39.2k Load Regulation (with respect load) (VLVOUT 1.8V), VLVIN 2.2V ILVOUT 100mA 54.9k, 39.2k (VLVOUT 1.8V), VLVIN 3.7V ILVOUT 150mA 1.73 1.75 VBAT 2.8V 1.95 VBAT 2.05
1.85
0.75
1.85
VLVOUT_LOAD
SC908
Electrical Characteristics (continued)
Parameter Symbol Conditions Units
Linear Drop-Out (LDO) Regulator (continued) Line Regulation VLVOUT_LINE 2.2V VLVIN 4.2V referenced 3.7V, ILVOUT 1mA, 54.9k, 39.2k VLVIN 3.7VDC with 0.5V P-to-P Ripple, PSRRLLVIN 10kHz, VBAT 3.7VDC VLVOUT 1.8V, ILVOUT 30mA VLVIN VBAT 3.7VDC with 0.5V P-to-P PSRRLBAT Ripple, 10kHz VLVOUT 1.8V, ILVOUT 30mA 10Hz 100kHz Output Noise Voltage
LVOUT/LVIN Power Supply Rejection Ratio
LVOUT/(BAT LVIN) Power Supply Rejection Ratio
VL_NOISE
CLVOUT VLVOUT 3.0V VLVIN 3.7V, ILVOUT 50mA VLVIN VLEN VBAT 4.2V, VVAD ILVOUT VLVOUT VLEN VBAT Time from (with VSEN VBAT, disregard tSU_REF), VLVOUT from final Time from (with VVAD VSEN tSU_REF dominates) VLVOUT from final Time from VLVOUT from 100% regulation
VRMS
Quiescent Current (ILVIN ILVOUT Current Limit
IL_LIM
Start-Up Time
tSU-LVOUT
Turn-Off Time Battery Voltage Detector Battery Detector Minimum Operating Voltage Battery Detector Maximum Operating Voltage Battery Detector Voltage Warning, Decreasing Battery Detector Voltage Fault, Decreasing Battery Detector Threshold Hysteresis, Warning Fault
tTO-LVOUT
VDET_MINOP VDET_MAXOP VWARN VDET VDET_HYS VDET_MINOP VBattery VDET_MAXOP RRLBAT 309k VDET_MINOP VBattery VDET_MAXOP
3.21
3.28
3.35
2.92
SC908
Electrical Characteristics (continued)
Parameter Symbol Conditions Units
Logic Control Inputs Status Outputs Battery Detector Sense Leakage (BSEN Current) Battery Detector Activation Delay(10) Logic Input Logic Input High Logic Input Current High Logic Input Current CPB, CHRGB, FLTB, LBATB Outputs IBSEN_DET VDET_DEL VVAD VADUVLO, high, VBSEN 4.2V Time from first high until LBATB/FAULTB valid, VVAD LEN, SEN; VBAT 2.7V LEN, SEN; VBAT 2.7V LEN, SEN; VBAT 2.7V LEN, SEN; VBAT 2.7V ISINK (VVAD CPB)
Notes: VADOP "Maximum Vsupply" defined EIA/JEDEC Standard paragraph 2.11. value buck converter disabled battery leakage current included charger section battery leakage since cannot independently measured (because SVIN tied internally). buck converter contribution this value also included Buck Converter section design guidance only. VSYS regulation voltage assumes that VVAD exceeds VVSYS VSYS regulator dropout (typically 0.5V 5mA, minimum regulator 71). this condition met, then VVSYS VVAD minus VSYS regulator dropout. IQ-Core supply current from battery common reference circuits into when either buck converter charger enabled. tSU_REF start-up time voltage reference buffer both DC-DC buck converter LDO, should added start-up time (tSU-SVOUT tSU-LVOUT respectively) first regulator enabled. case start-up with switcher disabled, start-up time tSU-LVOUT concurrent with reference start-up time tSU_REF, tSU-LVOUT specified typically zero. SVOUT buck converter output node, which node which output inductor connected load. feedback resistor divider network. Typical Application Circuit. guarantee positive load threshold hysteresis PSAVE-to-PWM mode switching with SVOUT 2.2V, contact your Semtech representative application assistance. VBAT VSVOUT_Max SDCMAX 150mV, then maximum output setting VBAT SDCMAX 150mV. Higher output voltage settings feasible, subject load-dependent dropout. Specified with VBAT VLVIN. (10) Guaranteed design.
SC908
Typical Characteristics
Charger Line Regulation
IBAT 50mA 4.19 4.189 4.188 4.187 4.19 4.189 4.188 4.187
Charger Load Regulation
VVAD
VBAT
4.185 4.184 4.183 4.182 4.181 4.18
VBAT
4.186
4.186 4.185 4.184 4.183 4.182 4.181 4.18
VVAD
IBAT (mA)
Charger Temperature Regulation
VVAD IBAT 50mA 4.186 4.184 4.182 4.18 4.178 4.176 4.174 4.172
Charger Line Regulation
VBAT 3.75V, RIPRGM 6.04k
IBAT (mA)
VBAT
4.75
5.25
5.75
6.25
6.75
Junction Temperature
VVAD
Charger VBAT Regulation
VVAD RIPRGM 6.04k 178.75 178.5 178.25
Charger Programming
-40, VVAD VBAT 3.75V
IBAT (mA)
IBAT (mA)
177.75 177.5 177.25 176.75 176.5 176.25
VBAT
RIPRGM
SC908
Typical Characteristics (continued)
PreQ VBAT 2.6V, RITERM 4.99k
41.5 40.5
Charger
Line Regulation
Charger IPreQ Programming
VVAD VBAT 2.6V
IBAT (mA)
39.5 38.5
IBAT (mA)
4.75
5.25
5.75
6.25
6.75
VVAD
RITERM
Charging Cycle Battery Voltage Current
700mAhr battery, RIPRGM 2.15k, RITERM 3.48k, VVAD 5.0V,
Pre-Charging Battery Voltage Current
700mAhr battery, RIPRGM 2.15k, RITERM 3.48k, VVAD 5.0V,
VBAT (V), Internal Power Dissipation
VBAT (V), Internal Power Dissipation
0.25 0.75 1.25 1.75 2.25 IBAT VBAT
VBAT IBAT
IBAT (mA)
Time (hrs)
Time
CC-to-CV Battery Voltage Current
700mAhr battery, RIPRGM 2.15k, RITERM 3.48k, VVAD 5.0V, IBAT
Re-Charge Cycle Battery Voltage Current
700mAhr battery, RITERM 3.48k, VVAD 5.0V, Load 10mA
VBAT (V), Internal Power Dissipation
IBAT
VBAT
IBAT (mA)
VBAT 56.5 57.5 58.5 59.5
Time (min)
Time (hrs)
IBAT (mA)
VBAT
IBAT (mA)
SC908
Line Regulation
54.9k, 39.2k, 1.799 ILVOUT 10mA 1.798 ILVOUT 100mA 1.799
Load Regulation
54.9k, 39.2k, VLVIN 3.75V
ILVOUT 50mA 1.7985
VLVOUT
VLVOUT
1.797 ILVOUT 150mA 1.796
1.798
1.7975
1.795
1.797
VLVIN
ILVOUT (mA)
Temperature Regulation
54.9k, 39.2k, VLVIN 3.75V ILVOUT 10mA 1.795 ILVOUT 100mA 1.79 ILVOUT 50mA 1.775 1.77
PSRR, LVIN LVOUT
VLVOUT 1.8V, VLVIN 3.7VDC 0.5VAC, VBAT 3.7V
ILVOUT 150mA 1.785
1.78
PSRR LLVIN (dB)
VLVOUT
1000
10000
Junction Temperature
Frequency (Hz)
PSRR, LVOUT
VLVOUT 1.8V, VLVIN 3.7VDC, VBAT 3.7VDC 0.5VAC
PSRR, LVIN LVOUT
VLVOUT 1.8V, VLVIN VBAT 3.7VDC 0.5VAC
1000
10000
PSRR LBAT (dB)
PSRR (dB)
1000
10000
Frequency (Hz)
Frequency (Hz)
SC908
Typical Characteristics (continued)
DC/DC Converter Line Regulation
VSVOUT 2.2V (RS1 340k, 100k), 2.23 ISVOUT 35mA 2.22 ISVOUT 10mA PSAVE Mode 2.22 2.25 2.24 2.23
DC/DC Converter Load Regulation
VSVOUT 2.2V (RS1 340k, 100k), VBAT 3.7V
VSVOUT
VSVOUT
2.21
2.21 Decreasing Load 2.19 2.18 2.17 Increasing Load
ISVOUT 100mA 2.19 ISVOUT 150mA 2.18 Mode
2.16 2.15
VBAT
ISVOUT (mA)
DC/DC Converter Temperature Regulation
VSVOUT 2.2V (RS1 340k, 100k), VBAT 3.7V 2.23 ISVOUT 35mA 2.22 ISVOUT 10mA PSAVE Mode
DC/DC Converter Efficiency
VSVOUT 2.2V (RS1 340k, 100k), VBAT 3.6V,
PSAVE Mode
Mode
Efficiency
ISVOUT 100mA Mode ISVOUT 150mA
VSVOUT
2.21
2.19
2.18
Junction Temperature
ISVOUT (mA)
DC/DC Converter Efficiency Detail
VSVOUT 2.2V (RS1 340k, 100k), VBAT 3.6V, PSAVE Mode PSAVE Mode Mode
DC/DC Converter Efficiency Loads
VSVOUT 2.2V (RS1 340k, 100k), VBAT 3.6V,
Efficiency
Mode
Efficiency
ISVOUT (mA)
ISVOUT (mA)
SC908
Descriptions
Name
VSYS IPRGM ITERM RTIME RLBAT LVIN LVOUT VREF AGND DGND FLTB LBATB
Function
Charger input Adapter input internal-regulation node which also serves supply EN_NTC, RTIME, input-referenced (vs. battery-referenced regulated output-referenced) pull-ups; load must exceed 5mA. setting constant current charging current connect resistor ground current. setting termination precharge current connect resistor ground current. Charge timer connect resistor ground timer, ground disable timer. Timer enabled with internally programmed default time selected with RTIME tied VSYS. Resistor connected ground Battery voltage threshold. voltage input connected either battery supply (BAT) switching regulator output (SVOUT). other connections permitted. voltage output feedback voltage input Bandgap reference bypass connected 10nF capacitor analog ground. other connections permitted. Analog ground refer grounding considerations application section. Digital ground refer grounding considerations application section. enable active high DC-DC converter feedback input connect voltage divider from output this output voltage. Charging Fault indicator open drain output active when charging fault occurred. Also, together with LBATB, indicates when battery discharges below programmable voltage RLBAT resistor. Battery indicator open drain output active when battery discharges below 3.3V, and, together with LBATB, indicates when battery discharges below programmable voltage RLBAT resistor. Charger Present indicator open drain output active when valid input voltage present. DC-DC converter enable active high Charging-In-Progress indicator open drain output active when charging until charging current drops below programmed termination current, until charging disabled charge timeout EN_NTC disable temperature fault. DC-DC converter power ground other connection permitted. DC-DC converter output connect inductor between this point SVOUT (the DC-DC converter load connection). Charger output pin, also DC-DC converter input connect positive battery terminal. thermistor input charger enabled voltage between VSYS 0.75 VSYS. Charger disabled voltage below Battery temperature fault otherwise. Battery Kelvin sense independent connection tied directly battery positive terminal. Connect ground plane with thermal vias directly under pad.
CHRGB
PGND EN_NTC BSEN Thermal
SC908
Block Diagram With Typical Application Circuit
Charging Adapter
VSYS
VSYS Regulation VSYS 4.2V Reference Voltages VREF Qterm Qpass
CVSYS
CVAD
VREF
BSEN
Fast Charge Pre-Charge CVREF VTH-cold
(0.75VCC)
VTH-hot
(0.3VCC)
RNPU
EN_NTC Interface
Control
Pre-Charge Fast Charge Over Temp Under Voltage Over Voltage
Pre-Charge
CVOUT
RNTC RRTIME
ITERM RTIME Timer Fast Charge CHRGB VREF LVIN IPRGM
RITERM
RIPRGM
CLVIN
FLTB LBATB
LVOUT
Supply from battery SVOUT
CLVOUT
AGND RRLBAT
RLBAT
SVIN
Buck Converter Control Block
PGND DGND
CSFG
CSFB
SVOUT
CSVOUT
SC908
Applications Information
Charger Operation
SC908 Li-Ion battery charger configured independently with respect fast-charge, termination current, timing. charging battery voltage status indicated four status outputs. charge cycle initiated when power adapter connected device SC908 voltage between Under-Voltage LockOut (UVLO) rising threshold input Over Voltage Protection (OVP) threshold. battery voltage less than pre-charge threshold, output current regulated programmed precharge current. When pre-charge threshold voltage exceeded, fast-charge Constant Current (CC) mode begins, with charge current rising programmed fast-charge current three soft-start current steps. charger enters Constant Voltage (CV) mode when battery voltage rises final value (VCV typically 4.2V. mode voltage regulated VCV, battery continues charge accepts decreasing current. CHRGB output turns when IBAT drops below programmed termination current. charge timer active, battery held charge mode until timer cycle ends. charger then enters monitor mode, where output remains until voltage drops VTReQ, charge cycle initiated. charge timer disabled, monitor mode immediately entered upon charge termination. when cycled when EN_NTC forced disable charger.
Fast-Charge Constant Current Mode
fast-charge mode active when battery voltage above VTPreQ less than VCV. current maximum 0.5A selected program resistor IPRGM pin. voltage this represents charger output current. This allows charging current measured sensing IPRGM voltage using general purpose Analog-toDigital Converter (ADC) host microporocessor. fast-charge current determined
VIPRGM RIPRGM
Excellent fast-charge current accuracy obtained patented polarity-switched current sense amplifier Patent 6,836,095). This nullifies current measurement offset errors, leaving only small gain error. range expected fast-charge output current versus programming resistance RIPRGM shown Figures
Fast Charge Current (mA)
Pre-Charge Mode
pre-charge mode automatically entered when battery voltage below pre-charge threshold voltage, which preconditions battery fast charging. pre-charge current value resistor ITERM pin, programmable from 14mA 65mA. precharge current determined
VITERM RITERM
RIPRGM
where VITERM_Typ designates typical value VITERM. (See Termination Current section precharge current accuracy.) When timer enabled, there maximum allowed pre-charge duration. pre-charge time exceeds total charge cycle, charger will turn pre-charge fault. This fault cleared
Figure Fast-charge Current Variation IPRGM Resistance, Resistance Range
SC908
Applications Information (continued)
Fast Charge Current (mA)
10.5 11.5 12.5 13.5 14.5
RIPRGM
Figure Fast-charge Current Variation IPRGM Resistance, High Resistance Range figures show nominal current versus nominal RIPRGM resistance center plot theoretical limit plots indicating maximum minimum current versus nominal programming resistance. These plots derived from models expected worst-case contribution error sources depending programmed current. current range includes uncertainty tolerance resistors. dots each plot indicate currents obtained with standard value tolerance resistors. figures show high resistance ranges.
Termination current programmed from 14mA 65mA, must less than correct operation charge cycle. Pre-charge termination current regulation accuracy dominated offset error. range expected pre-charge output current termination threshold current versus programming resistance RITERM shown Figures figures show nominal pre-charge termination current versus nominal resistance center plot. theoretical limit plots indicate maximum minimum current versus nominal programming resistance. These plots derived from models expected worst-case contribution error sources depending programmed current. current range includes uncertainty tolerance resistors. dots each plot indicate currents obtained with standard value tolerance resistors. figures show high resistance ranges. sufficient separation between ITERM must maintained ensure proper operation constant current regulator charge termination detector. RIPRGM RITERM must chosen nominally satisfy ITERM 90mA
Precharge/Termination Current (mA)
Termination Current
When battery voltage reaches VCV, SC908 transitions from constant current mode constant voltage mode. output holds voltage measured BSEN constant, current through battery will decrease battery becomes fully charged. CHRGB disabled when output current drops below programmed termination current. timer enabled, output will continue float-charge mode until charge timer expires. timer disabled, output will turn soon termination current level reached. termination current determined
VITERM RITERM
RITERM
Figure Pre-charge Termination Current Variation ITERM Resistance, Resistance Range
ITERM
SC908
Applications Information (continued)
Precharge/Termination Current (mA)
battery voltage falls below recharge threshold (VCV VReQ), charger will clear charge timer initiate charge cycle. status charger output function Charge Complete timer status IBAT shown Table Table Charger Output Status
Timer
Iout
Itermination
Output State
Timeout
Timeout Disabled
10.5
11.5
12.5
13.5
RITERM
Remote Kelvin Sensing Battery
BSEN provides Kelvin sensing battery positive terminal voltage. This prevents feedback error charging, battery load, switching regulator input currents flowing over resistive traces. Optimal layout routes BSEN trace directly battery positive terminal connection achieve most accurate sensing battery cell voltage. Connecting BSEN directly SC908 will introduce battery voltage measurement error that cause improper transition from regulation, lengthening charge time. This error could also raise lower final battery voltage, alter final state-of-charge.
Figure Pre-charge Termination Current Variation ITERM Resistance, High Resistance Range
Charge Timer
timer provides over-charging protection event faulty battery maximizes charging capacity. RTIME connected VSYS select internal (default) time duration three hours, disable timer. Connecting resistor between RTIME will program Charge Complete Time-Out, hours, according equation
QComp RRTIME 3.334 3600
timer programmable over range hours. output automatically turned when charge timer cycle ends. charge cycle remains precharge longer than fourth Charge Complete Time-Out period, charging fault detected charger turns off. Precharge Fault Time-Out period, minutes,
QComp
EN_NTC Interface
EN_NTC interface battery pack temperature sensing Negative Temperature Coefficient (NTC) thermistor, which used suspend charging battery pack temperature outside safe-to-charge range. also charger-disable input. typical EN_NTC network fixed resistor from VSYS EN_NTC pin, battery pack EN_NTC thermistor from EN_NTC ground. this configuration, increasing battery temperature produces decreasing voltage. When VEN_NTC greater than high (cold) threshold less than (hot) threshold, charge cycle suspended turning output. This suspends does reset charge timer, indicates fault FLTB pin. Hysteresis included both high
Monitor Mode
When charge cycle complete (termination timer disabled, charge timeout timer enabled), output turns device enters monitor mode.
SC908
Applications Information (continued)
thresholds avoid chatter fault thresholds. When VEN_NTC returns valid range, charge timer resumes charge cycle continues. charge timer will expire when output on-time exceeds timer setting, regardless long been disabled fault. Using recommended external network, EN_NTC voltage internal cold thresholds ratios VVSYS, rather than absolute voltages. This ensures that cold OK-to-charge thresholds insensitive VSYS output voltage. ratiometric thresholds given parameters RTNTCH RTNTCC. EN_NTC voltage VEN_NTC between enables charging. When VEN_NTC outside this range, charging suspended FLTB output asserted (pulled low). When VEN_NTC VTNTCDIS (nominally 0.6V), SC908 charger disabled. EN_NTC pulled ground external n-channel microprocessor GPIO asnychronously disable reset device. When VEN_NTC VTNTC_DIS, charger turned off, charge timer reset, CHRGB status output turned off. While disabled, input UVLO threshold detectors remain active, continues indicate whether input voltage valid charging. response SC908 EN_NTC voltage above high threshold below threshold (but above VTNTCDIS) same. Therefore EN_NTC network configured with battery pack thermistor between EN_NTC VSYS, fixed resistor between EN_NTC ground. This configuration used reset charge timer (and CHRGB output) when battery pack removed; fixed resistor pulls ground disable charger without indicating fault. sheet proposed thermistor, Mitsubishi TH11-3T223F, indicates that RNTC 11.93k 40°C, 69.41k 0°C, with dissipation constant 3.0mW/°C. RHOT 11.93k RCOLD 69.41k. Step Select RNPU obtain desired temperature thresholds. This example will solve threshold normal (NTC thermistor ground) configuration, then evaluate cold threshold. Solve network voltage divider place voltage RTNTC_HF VVSYS when RNTC RHOT.
RTNTC VVSYS VVSYS RHOT RNPU RHOT
solving RNPU,
RNPU RTNTC RHOT RTNTC
Using RTNTC_HF 0.3, obtain RNPU 27.837k exactly. closest standard nominal value RNPU 28.0k. Step Evaluate network cold threshold. Compute network resistor divider voltage function VVSYS desired cold threshold.
COLD VVSYS COLD COLD 0.7126 VVSYS
value 0.7126 should close nominal value RTNTC_CR 0.75. evaluate significance discrepancy, estimate actual cold threshold obtained evaluating value NTC_Cold_Actual that produces nominal value NTC_CR 0.75.
RTNTC RNTC Cold Actual RNTC Cold Actual RNPU
Design Example
This example uses conventional network configuration shown block diagram. fixed resistor (RNPU) connected between EN_NTC VSYS, battery thermistor (RNTC) connected between EN_NTC ground. battery temperature range over which charging permitted from 40°C. data-
solution shows RNTC_Cold_Actual 84.0k. Examination thermistor specification resistance versus temperature data indicates that resulting actual cold threshold approximately -4°C, compared target 0°C.
SC908
Applications Information (continued)
Step With example thermistor, there choice RNPU that will yield specified results both cold limits. more sensitive thermistor, with wider percentage variation resistance desired threshold temperatures, provide better solution. Steps repeated using other devices from same vendor, seeking closer match cold threshold. Mitsubishi TH11-4C153F final selection. characteristics are: RHOT 7.73k 40°C), RCOLD 53.94k 0°C). dissipation constant 3.0mW/°C. Step yields RNPU 18.2k, with result that NTCCOLD/VVSYS 0.748 RTNTC_CR, NTCHOT/VVSYS 0.298 RTNTC_HF. resistances that give exact cold thresholds RTNTC_CR RTNTC_HF 54.6k (which RNTC approximately -0.5°C) 7.80k respectively, closely matching resistance thermistor targeted threshold temperatures. Step Verify acceptable thermistor self heating. dissipation constant power rating thermistor resulting self heating error. Since accuracy important only thresholds, self heating assessed only 40°C. VVSYS 4.6V, network current INTC_COLD VVSYS/(RNPU RCOLD) 63.8A Power dissipation thermistor this temperature PCOLD RCOLD (INTC_COLD)2 0.219mW self heating error
COLD 0.219mW 0.073
self heating approximately 0.081°C. actual cold thresholds will 0.073 0.081 degrees lower than designed, respectively, which negligible errors.
Logical CC-to-CV Transition
SC908 differs from most monolithic linear single cell Li-Ion chargers, which implement linear transition from regulation. linear transition method uses simultaneous feedback signals output voltage output current closed-loop controller. When output voltage sufficiently below regulation voltage, influence voltage feedback negligible output current regulated desired current. battery voltage approaches regulation voltage (4.2V), voltage feedback signal begins influence control loop, which causes output current decrease although output voltage reached 4.2V. output voltage limit dominates controller when battery reaches 4.2V eventually controller entirely regulation. This system characterized dual-constraint (voltage current) controller, with soft transition between constraints. soft transition effectively reduces charge current below that which permitted portion charge cycle, which increases charge time. SC908, logical transition implemented from recover charge current lost soft transition. controller regulates only current until output voltage exceeds transition threshold voltage. then asynchronously switches regulation. transition voltage from regulation typically less than 10mV higher than regulation voltage, which provides sharp clean transition free chatter between regulation modes. difference between transition voltage regulation voltage CC/CV overshoot. While regulation, output current limited approximately 105% fast-charge current programmed IPRGM IPUSB pin, depending charging input selected, providing mode transition hysteresis. output current exceeds this current limit threshold, controller asynchronously reverts current regulation. logical transition from results fastest possible charging cycle that compliant with speci19
40°C network current INTC_HOT VVSYS/(RNPU RHOT 0.177mA Power dissipation thermistor this temperature PHOT RHOT (INTC_HOT 0.243mW
SC908
Applications Information (continued)
fied current voltage limits Li-Ion cell. output current constant limit, then decreases abruptly when output voltage steps from overshoot voltage regulation voltage transition control. This compared voltage current trajectories other monolithic charger devices show softness linear crossover. This explains charge-time advantage SC908 logical crossover method. Input Over-Voltage Protection input protected from adapter over-voltage least above VDGND. When VVAD exceeds rising threshold VADOVP-R charger turns output while charge timer continues run, FLTB status indicator asserted. When VVAD subsequently falls below falling threshold VADOVP-F, charging continues normally FLTB released. Thermal Protection charger's internal over-temperature (OT) threshold approximately 145°C. temperature exceeds this threshold prior termination, charger output turned off. other functions remain active, charger logical state preserved, fault indicated. This allows thermal pulse charging conditions high power dissipation. Following termination, charger condition will indicated fault. Refer Indicator Flags subsection more information. second high threshold approximately 165°C. Should temperature exceed this threshold, SC908 functions disabled, status outputs indicate exceptional condition fault. Refer Indicator Flags subsection more information.
Charger Protection Features
protection features are:
Short Circuit Protection Over Current Temperature Protection Input Overvoltage Protection Thermal Protection
Short Circuit Protection output tolerate indefinite short circuit ground. current into ground short will equal precharge current. ITERM voltage prior termination, IPRGM voltage while mode, regulated 1.5V. Precharge current termination current proportional resulting ITERM current, current proportional resulting IPRGM current. High battery current prevented pinshort detectors both programming pins. Pinshort detection asynchronously forces charger into reset, turning output clearing charge timer. When pinshort condition removed, charger begins normal operation automatically. Over Current Temperature Protection Over current protection provided modes operation. When device charge mode output current-limited either programmed pre-charge current programmed fast charge current, depending voltage output. Junction over-temperature protection allows operation with maximum power dissipation disabling charger output current when temperature reaches maximum operating temperature. This results operation pulse charger extreme power dissipation applications, delivering maximum allowable output current while limiting internal temperature safe level.
Battery Detector Operation
battery detector provides battery detection voltage thresholds: fixed warning threshold resistor programmable detection (shutdown request) threshold. battery detector enabled when either buck converter enabled (SEN high) regulator enabled (LEN high). warning shutdown request provided status output pins FLTB LBATB, described Status Outputs subsection. When charging adapter present VADUVLO-x), FLTB LBATB outputs redefined reflect interaction battery voltage charging state. battery detector warning threshold fixed 3.28V 70mV. battery voltage fault threshold programmable, with resistor from RLBAT ground,
SC908
Applications Information (continued)
from 2.77V 2.98V, ±10%. battery fault threshold relationship VDET RRLBAT 2.42 RRLBAT must satisfy condition 294k RRLBAT 316k Connect RLBAT disable Battery Detector fault. Battery Detector warning remains active. CHRGB output indicates battery charging status. charger-present status output states described Table When pre-charging when output current greater than ITERM, CHRGB low. CHRGB output latched (high) when output current becomes less than ITERM during charge cycle (and battery voltage above recharge threshold, VBSEN VTReQ). This latch reset when battery enters recharge cycle (VBSEN VTReQ), NTC_EN range other than OK-to-charge, VVAD above below validto-charge range, allowing CHRGB become active again when charging resumes. When charging adapter present, FLTB LBATB outputs redefined reflect interaction battery voltage, charging state, charging faults, described Table FLTB output activated when device experiences charger fault condition, (together with LBATB output) when battery voltage less than resistor-programmed low-battery detector threshold, VDET. This output used notify system controller fault condition when connected interrupt input, used like CHRGB drive indicator LED. When VVAD between UVLO thresholds, VVAD valid charge, output indicating that charging adapter present.
Status Outputs
Four charger status outputs/LED drivers provided.
(Charger Present) CHRGB (Charge Active) FLTB (Fault) LBATB (Low Battery Warning)
These outputs active-low, open drain NMOS drivers capable sinking each. state each, various operating conditions, defined Tables When voltage below UVLO threshold charging adapter present), CHRGB outputs (high impedance). FLTB LBATB outputs indicate battery voltage defined Table
Table Status Output State, Charging Adapter Absent
Conditions Status Pins Output State low) Adapter Voltage (mutually exclusive)
VADUVLO VVAD VADOVP
Description Comments
VWARN VBSEN VDET
Battery Voltage (mutually exclusive)
VVAD VADUVLO
VVAD VADOVP
VBSEN VWARN
VDET VBSEN
open drain output driver active output active listed condition true listed condition false don't care Blank mutually exclusive with another condition Charging Adapter, Battery Voltage Good
CHRGB
LBATB
FLTB
Charging Adapter, Battery Voltage Warning Charging Adapter, Battery Shutdown Request
SC908
Applications Information (continued)
fault modes signaled FLTB are:
When these conditions occurs FLTB output goes low; otherwise remains high impedance. LBATB output active when battery voltage below low-battery warning voltage, VWARN, charging adapter absent. CHRGB outputs both active, LBATB indicates when charger precharge mode. However, LBATB FLTB active together always
input over-voltage battery temperature range pre-charge timeout. charger-only over-temperature (low posttermination only)
Table Status Output State, Charging Adapter Present
Conditions Status Pins Output State low) Adapter Voltage (mutually exclusive)
VADUVLO VVAD VADOVP
Battery Voltage (mutually exclusive)
EN_NTC (mutually exclusive)
Charging State, Charging Faults (Internal signals)
Description Comments
Pre-Charge Timeout
Pre-Term Charging
VWARN VBSEN VDET
Short-to-GND
Cold
VVAD VADUVLO
Pre-Charging
VVAD VADOVP
VBSEN VWARN
Charger
VDET VBSEN
open drain output driver active output active listed condition true listed condition false don't care Blank mutually exclusive with another condition
Disable
CHRGB
LBATB
FLTB
VVAD valid, Charger Disable/Reset Charging Done (Die Temperature VVAD valid Battery Warning, Charger Disable/Reset Charge Cycle Pending (about begin) VVAD valid, Battery Temperature Fault Charger Over-Temp Fault (Die Temp TCHRGR_OT VVAD valid, Battery Detected, with either Charger Disable/Reset Battery Temperature Fault Charger Over-Temp Fault short-to-ground VVAD valid, Pre-termination Charging, Battery Voltage VDET VVAD valid, Pre-Charging (trickle charging), Battery Voltage VDET VVAD valid, Pre-Charging with Charger Over-Temp Fault, Battery Voltage VDET VVAD valid, Battery Voltage VDET Pre-Charging Pre-Termination Charging
SC908
Applications Information (continued)
indicates that battery voltage below low-battery detect threshold, VDET. Table gives comprehensive description combinations status output states while adapter input valid charging. Exceptions these charging conditions occur when certain events happen combination. Table describes status condition exceptions. These exceptions include VVAD threshold; high over temperature condition, which device temperature exceeds higher over-temperature thresholds, causing charging both regulators disabled; precharge timeout, which indicate faulty battery. load VSYS should exceed 5mA. CHRGB used operate indicator LED, recommended that CHRGB status pulled battery battery-powered regulated supply. Since CHRGB asserted only while charging battery, current sunk CHRGB will sourced charger output will discharge battery. Because VSYS powered from VAD, unsuitable pullup source FLTB LBATB status pins. These status pins must powered from battery batterypowered regulated supply function battery level indicators when charging adapter present.
VSYS
voltage VSYS regulated from input present only when powered. VSYS provides external voltage reference supply network, pull-up supply voltage status indicator. capacitor least 0.1uF should connected from VSYS ground near pin.
Capacitor Selection
cost, ceramic capacitors such dielectric material types recommended. capacitor, CBAT, range 22F. This capacitor functions both charger output capacitor switching regulator input capacitor. input capacitor CVAD typically between 0.1F 2.2F; however, larger values will degrade performance.
Table Status Output State, Exception Conditions
Conditions Status Pins Output State low) Adapter Voltage (mutually exclusive)
VADUVLO VVAD VADOVP
Battery Voltage (mutually exclusive)
EN_NTC (mutually exclusive)
Charging State, Charging Faults (Internal signals)
Description Comments
Charger (High
Pre-Charge Timeout
Pre-Term Charging
VWARN VBSEN VDET
Short-to-GND
Cold
open drain output driver active output active listed condition true listed condition false don't care Blank mutually exclusive with another condition Overvoltage, Battery Voltage Good Warning Overvoltage, Battery Detect High-Over-Temperature Detection (die temperature TOT; functions shutdown.) Pre-charge Timeout, Disable, Adapter Voltage Good
VVAD VADUVLO
Pre-Charging
VVAD VADOVP
VBSEN VWARN
VDET VBSEN
Disable
CHRGB
LBATB
FLTB
SC908
Applications Information (continued)
Regulator
low-noise low-dropout (LDO) voltage regulator operates from LVIN input voltage range 2.2V battery voltage (VBAT output voltage from 1.5V 3.3V, programmable with external resistors. SC908 VREF bypass enable user capacitively decouple bandgap reference (10nF recommended) very output noise (50VRMS typically). output voltage regulator divided externally using resistor divider compared buffered bandgap voltage, typically 0.75V. error amplifier drives gate RDS(ON) P-channel MOSFET pass device. 1.5V 3.3V external resistor divider network from LVOUT LFB. output voltage
high impedance input, large value resistors, even order 500k, used meet noise specification. When considering effect load current performance specifications, current flowing feedback divider network should included load. internally compensated. feedback capacitor required stability.
Dropout
dropout voltage product minimum RDS(ON) P-channel MOSFET pass device output current. VLVIN decreases, achievable sourceto-gate voltage pass device decreases, minimum achievable RDS(ON) becomes larger. This reason two-tier dropout specification. Minimum RDS(ON) increases with temperature, which affected only power dissipation, also switching regulator charger power dissipation. maximum dropout specified temperature 85°C.
Enabling
independent enable input (active high). enabled only VLVIN VTLUVLO, typically 2.0V, although performance specifications guaranteed VLVIN 2.2V. output will settle within final value 0.1ms (typically) when bandgap reference buffer already settled (when switching regulator already enabled, when charging adapter present). fast start-up circuit used speed initial charging time VREF bypass capacitor. This done that output voltage will settle within final value 0.4ms (typically) when first resource enabled. When battery charger precharge mode operation (trickle charging deeply discharged battery), enable signal will disregarded until fast-charging begins battery voltage 2.8V typically). exception occurs when either switching regulator already enabled. this time when charging source applied charger enters precharge mode, will remain enabled become enabled). Precharge mode indicated status outputs. (Refer Table provides active shutdown. capacitance LVOUT will discharged on-chip when disabled.
Reference Voltage
internal bandgap reference voltage must externally bypassed meet noise specification. 10nF ceramic capacitor from VREF AGND recommended bypass bandgap reference buffer. Increasing this capacitor 100nF will improve power supply rejection, cost slower turn-on settling time. noise turn-on settling time specifications assume that VREF bypass capacitor 10nF. cost, ceramic capacitors such dielectric material types recommended. bandgap reference trimmed buffered obtain 0.75V typically with respect AGND while operating. VVREF reference voltage LFB, VVREF will equal VLFB within offset error feedback error amplifier. bandgap reference reference buffer powered from greater VSYS (derived from VAD, when present) VBAT (the battery voltage). PSRRREF specification with respect VBAT. evaluated while charging adapter present.
Programming Output Voltage
regulates output obtain 0.75V pin. output programmed voltage from
SC908
Applications Information (continued)
VREF power supply rejection with respect will similar. VREF high impedance source. load VREF will degrade switching regulator voltage accuracy. Note that impedance typical oscilloscope probe large enough prevent loading VREF pin. improving overall load transient response, also improve input supply rejection.
Switching Regulator
SC908 contains synchronous step-down Pulse Width Modulated (PWM), DC-DC converter (also referred Buck Converter Switcher) with integrated power devices. switching frequency nominally 1MHz, allowing small inductors capacitors. current limit internal PMOS switch (ILIM_P), allows output current least 150mA with appropriate external components. maximum efficiency over full load range, switcher will automatically operate Power Save (PSAVE) mode with light loads, (normal switching) mode heavier loads. voltage feedback loop uses external feedback divider. internal synchronous NMOS side switch used. external Schottky diode required.
Power Supply Rejection
Power supply rejection must considered with respect inputs. buffered bandgap reference powered greater possible sources, VVSYS internal/ external supply voltage, derived from when present) VBAT. powered from LVIN pin. PSRRL defined power supply rejection from LVIN LVOUT with reference reference buffer powered from voltage. reference voltage VREF power supply rejection specification (PSRRREF) with respect BAT. reference voltage power supply noise ripple seen noise reference voltage. This noise then gained-up output reciprocal divider network, gain RL1/RL2). special case VLVIN VBAT (the LVIN connected directly battery), power supply rejection LDO, PSRRLBAT, determined
PSRRLBAT log10
PSRR
Switcher Programmable Output Voltage
buck converter regulates output obtain 0.5V pin. output programmed voltage from 1.0V 3.0V external resistor divider network from external circuit node SVOUT pin. equation setting output voltage
PSRR
Current Limit Short-Circuit Protection
regulator current limit circuitry ensure that output current will damage device during output short-circuit ground, overload, start-up. current limit guaranteed greater than 200mA allow fast charging output capacitor high transient load currents.
high impedance input, therefore magnitude resistances used will determined trade between feedback network current product design practice. 25pF feedback capacitor, designated CSFB, required stability mode. When considering effect buck converter load current performance specifications, current flowing feedback divider network should included load. most situations, PSAVE mode operation will require capacitor from AGND. Refer PSAVE mode description.
Input Output Capacitor
minimum input output capacitance with maximum equivalent series resistance (ESR) less than over temperature recommended. Increasing output capacitance will further reduce output noise improve load transient response. larger input capacitor will reduce input droop load transients,
Switcher Power Save (PSAVE) Mode Operation
PSAVE mode automatically activated deactivated with light heavy loads, maximizing efficiency across
SC908
Applications Information (continued)
full load range. SC908 automatically detects load current which should enter PSAVE mode. This detection based minimum peak current PMOS high side switch mode. This will vary with input voltage, output voltage, converter external inductance (LS). PSAVE entry load current will decrease with decreasing PSAVE mode burst cycle, VSVOUT rises from lower upper voltage threshold with switching burst (see Figure Within burst, PMOS switch turned until PMOS current reaches current limit. then turned fixed duration, then turned again (cycle repeated). low-side NMOS switch turned whenever high-side switch off. When upper threshold (1.5% above programmed regulation voltage) reached, switching burst halted. This reduces quiescent current turning both highside low-side switches. VSVOUT decays lower threshold (0.8% above programmed regulation voltage) load current discharging output capacitor, which initiates another switching burst. burst-time off-time ratio PSAVE will decrease with decreasing load current.
PSAVE Mode Moderate Load
BURST BURST
lope frequency will exceed 20kHz load greater than 3mA, external component recommendations have been followed. envelope minimum frequency will decrease with increasing CSVOUT capacitance. SC908 automatically detects when exit PSAVE mode monitoring VSFB, thus VSVOUT. switching burst output current insufficient supply output load, VSVOUT will rise upper threshold during switching burst, will instead decrease. VSVOUT droops below programmed regulation voltage, PSAVE mode will deactivated, buck converter will revert immediately mode. prevent rapid PWM/ PSAVE mode cycling, PSAVE entry exit criteria chosen provide load hysteresis. After reverting mode switcher will remain mode switching cycles (approximately 128s) before permitted re-enter PSAVE mode. Proper operation PSAVE mode requires addition capacitor from ground, designated CSFG, value CSFG CSFB RS2.
Higher Load Applied
Switcher Efficiency
PSAVE Mode High Load
BURST
Mode High Load
Mode
+1.6%
VSVOUT
+0.8% Prog'd Voltage
Switcher efficiency affected input voltage, output voltage, temperature, choice inductor. also varies with load, which mode, PSAVE, active. mode selection depends only instantaneous load, also immediate past load, since transitions between PSAVE modes load dependent, with hysteresis. high loads (those that unconditionally place switcher mode), efficiency typically exceeds 90%. loads (those that unconditionally place switcher PSAVE mode), efficiency vary from over conditions. load decreases further, SC908 quiescent current eventually becomes significant, efficiency drops sharply. intermediate modes, switcher could select either PSAVE mode depending whether recent past load higher lower, load hysteresis. Within hysteresis load range, efficiency vary from 92%, over conditions.
Inductor Current
Time
Figure Power Save Operation PSAVE switching burst designed that inductor current ripple similar that mode. prevent audible noise, PSAVE mode parameters have been chosen such that minimum PSAVE burst enve-
SC908
Applications Information (continued)
Switcher Protection Features
protection features are: inductor should have minimize conduction losses maximize efficiency. minimum requirement, current rating inductor should equal maximum load current plus half inductor current ripple shown equation
(Peak IOUT(MAX
Current limit Over-voltage protection Soft-start
Current Limit PMOS power device buck switcher stage protected current limit function. short ground output occurs, part enters frequency foldback mode, which causes switching frequency divide factor determined output voltage. This prevents inductor current from stair-casing. Over-Voltage Protection event over-voltage output mode, drive disabled. When disabled, output becomes high impedance (both high-side low-side switches turned switcher will resume switching until output voltage fallen below programmed regulation voltage. Soft-Start soft-start mode enabled after every shutdown cycle limit in-rush current. This controls maximum current during start-up. PMOS current limit stepped using three soft-start levels full value timer driven from internal oscillator. During soft-start, switching frequency stepped 1/8, 1/4, internal oscillator frequency full value, under control three output voltage thresholds. When output voltage rises regulation voltage, softstart mode disabled.
Final inductor selection will depend various design considerations such efficiency, EMI, PSAVE entry, size cost. CBAT Selection CBAT functions both charger output capacitor switching regulator input capacitor. source input current buck converter non-continuous. prevent large input voltage ripple ceramic capacitor required. minimum value should used sufficient input voltage filtering should used improved input voltage filtering. CSVOUT Selection internal compensation designed operate with minimum output capacitor value 10F. Larger output capacitor values will improve transient performance. Output voltage ripple combination voltage ripple from inductor current charging discharging output capacitor voltage created from inductor current ripple through output capacitor ESR. Selecting output capacitor with will reduce output voltage ripple component, seen equation
VSVOUT (ESR ripple CSVOUT
Switcher External Components
SC908 designed with inductor 4.7H, although other values used. magnitude inductor current ripple dependent inductor value determined equation
VSVOUT VSVOUT fosc VVOUT
Capacitors with ceramic dielectric recommended their superior temperature voltage characteristics. capacitors should used their temperature coefficients make them unsuitable this application. When selecting output capacitor, essential that CSVOUT capacitance evaluated VSVOUT programmed voltage. specified capacitance 0402, even 0603, package size devices often severely derated just
This equation demonstrates relationship between input voltage, output voltage, inductor ripple current.
SC908
Applications Information (continued)
volts bias. This especially true inexpensive dielectrics. Insufficient SVOUT capacitance cause rapid decay output voltage between PSAVE bursts, resulting poor low-load efficiency, PSAVE/PWM mode cycling, other erratic behaviors.
Charger Grounding Layout Considerations
While layout linear devices generally critical switching application, careful attention detail will ensure reliable operation.
Switcher Grounding Layout Considerations
Poor layout degrade performance DC-DC converter contribute problems, ground bounce resistive voltage losses. Poor regulation instability result. simple design rules implemented ensure good layout:
Place inductor filter capacitors close device possible short wide traces between power components. Route output voltage feedback path away from inductor node minimize noise magnetic interference. Maximize ground metal component side improve return connection thermal dissipation. Separation between node should maintained avoid coupling switching noise ground plane. ground plane with several vias connecting component side ground further reduce noise interference sensitive circuit nodes.
Attaching part larger copper footprint will enable better heat transfer from device, especially PCBs with internal ground power planes. Place input, output bypass capacitors close device optimal transient response device behavior. Connect ground connections directly ground plane. there ground plane, connect common local ground point before connecting board ground. DGND PGND should connected directly ground plane close part possible. thermal should connected ground plane with thermal vias under SC908. nodes indicated AGND Block Diagram should connected together AGND pin. AGND should tied DGND single point close SC908. Route BSEN trace directly battery positive terminal connection PCB.
SC908
Outline Drawing MLPQ-24
DIMENSIONS MILLIMETERS INCHES .031 .035 .039 0.80 0.90 1.00 .000 .001 .002 0.00 0.02 0.05 (.008) (0.20) .010 .012 0.18 0.25 0.30 .007 .152 .157 .163 3.85 4.00 4.15 .100 .106 .110 2.55 2.70 2.80 .152 .157 .163 3.85 4.00 4.15 .100 .106 .110 2.55 2.70 2.80 0.50 .020 .012 .016 .020 0.30 0.40 0.50 0.10 .004 .004 0.10
INDICATOR (LASER MARK)
SEATING PLANE
NOTES: CONTROLLING DIMENSIONS MILLIMETERS (ANGLES DEGREES). COPLANARITY APPLIES EXPOSED WELL TERMINALS.
SC908
Land Pattern MLPQ-24
DIMENSIONS INCHES (.156) .122 .106 .106 .020 .010 .033 .189 MILLIMETERS (3.95) 3.10 2.70 2.70 0.50 0.25 0.85 4.80
NOTES: THIS LAND PATTERN REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES MET. THERMAL VIAS LAND PATTERN EXPOSED SHALL CONNECTED SYSTEM GROUND PLANE. FAILURE COMPROMISE THERMAL AND/OR FUNCTIONAL PERFORMANCE DEVICE.
Contact Information
Semtech Corporation Power Management Products Division Flynn Road, Camarillo, 93012 Phone: (805) 498-2111 Fax: (805) 498-3804
www.semtech.com

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