Dual-Output Power-Supply Controller Fixed 3.3-V Step-down Convert

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Dual-Output Power-Supply Controller Fixed 3.3-V Step-down Convert

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Si786
Dual-Output Power-Supply Controller
Fixed 3.3-V Step-down Converters Less than 500-mA Quiescent Current Converter 25-mA Shutdown Current 5.5-V 30-V Operating Range
DESCRIPTION
Si786 Dual Controller Portable Computer Power Conversion functionally compatible with MAX786 dual-output power supply controller notebook computers. device designed drop-in replacement that circuit. circuit system level integration step-down controllers, micropower 3.3-V linear regulators, comparators. controllers perform high efficiency conversion battery pack energy (typically output wall converter (typically 18-V 24-V 3.3-V system supply voltages. micropower linear regulator used keep power management back-up circuitry alive during shutdown step-down converters. comparators biased voltage between input voltage, simplifying battery monitoring providing sufficient voltage enhance gate on-resistance n-channel used switching power different zones system. complete power conversion management system implemented with Si786 Dual Controller Portable Computer Power Conversion, inexpensive linear regulator, Si9140 Controller High Performance Processor Power Supplies, five Si4410 n-channel TrenchFETR Power MOSFETs, Si4435 p-channel TrenchFET Power MOSFET, Si9712 Card (PCMCIA) Interface Switches. Si9130 Pin-Programmable Dual Controller Portable another integrated system level devices portable power systems. Si786 available both standard lead (Pb)-free 28-pin SSOP packages specified operate over (0_C 70_C), (-10_C 90_C) (-40_C 85_C) temperature ranges. Ordering Information corresponding part numbers.
FUNCTIONAL BLOCK DIAGRAM
5.5. SHUTDOWN ON/OFF 3.3-V ON/OFF SYNC Power Section
Memory Peripherals
Si786
Low-Battery Warning Power-Good
Document Number: 70189 S-40807-Rev. 26-Apr-04
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Si786
ABSOLUTE MAXIMUM RATINGS
-0.3 PGND -0.3V BST3, BST5 -0.3V BST3 BST5 Inputs/Outputs (D1, SHDN, ON5, REF, SS5, CS5. FB5, SYNC, CS3, FB3, SS3, ON3)) -0.3 -0.3 -0.3 DL3, PGND -0.3 -0.3 (BST3 -0.3 (BST5 REF, Short Momentary Current Current Continuous Power Dissipation 70_C)a 28-Pin SSOPb Operating Temperature Range: (TMIN TMAX) Si786CG/CRG/CSG (C-Grade) 70_C Si786LG/LRG/LSG (L-Grade) -10_ 90_C Si786DG/DRG/DSG (D-Grade) -40_ 85_C Lead Temperature (soldering, sec) 300_C Notes Device mounted with leads soldered welded board. Derate 9.52 mW/_C above 70_C.
Exposure Absolute Maximum rating conditions extended periods affect device reliability. Stresses above Absolute Maximum rating cause permanent damage. Functional operation conditions other than operating conditions specified implied. Only Absolute Maximum rating should applied time
SPECIFICATIONS
Specific Test Conditions Parameter
IREF SHDN Other Digital Input Levels TMIN TMAX
Limitse Mina Typb Maxa Unit
3.3-V Step-Down Controllers
Input Supply Range Output Voltage (CS5-FB5) (includes load line regulation) (CS3-FB3) (includes load line regulation) Si786CG/LG/DG Si786CRG/LRG/DRG Si786CSG/LSG/DSG 4.80 3.17 3.32 3.46 5.08 3.35 3.50 3.65 0.03 Si786DG/DRG/DSG Si786DG/DRG/DSG 5.20 3.46 3.60 3.75
Output Voltage Load Regulation Line Regulation Current-Limit Current Limit Voltage SS3/SS5 Source Current SS3/SS5 Fault Sink Current
Either Controller (CS_ Either Controller CS3-FB3 CS5-FB5
Internal Regulator Reference
Output Voltage Fault Lockout Voltage VL/FB5 Switchover Voltage Output Voltage Fault Lockout Voltage Load Regulation Shutdown Current Standby Current Quiescent Power Consumption (both controllers Current www.vishay.com Falling Edge, Hysteresis Rising Edge FB5, Hysteresis External Loadc Falling Edge SHDN 5.25 Si786DG/DRG/DSG 3.24 Si786DG/DRG/DSG 3.36
5.25 Switched Over
Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
SPECIFICATIONS
Specific Test Conditions Parameter Comparators
Trip Voltage Input Current Source Current Sink Current Output High Voltage Output Voltage Quiescent Current Falling Edge Hysteresis Edge, 1.61 Si786DG/DRG/DSG 1.60 1.69 1.69 "100 1000 IREF SHDN Other Digital Input Levels TMIN TMAX
Limitse Mina Typb Maxa Unit
VOUT ISOURCE ISINK External Load
Oscillator Inputs/Outputs
SYNC Oscillator Frequency SYNC SYNC High Pulse Width SYNC Pulse Width SYNC Rise/Fall Time Oscillator SYNC Range Maximum Duty Cycle Input Voltage Input High Voltage Input Current DL3/DL5 Sink/Source Current DH3/DH5 Sink/Source Current DL3/DL5 On-Resistance DH3/DH5 On-Resistance SYNC SYNC SHDN, ON3, SYNC SHDN, ON3, SYNC SHDN, ON3, VOUT BST3 BST5 VOUT High High BST3 BST5 Tested Si786DG/DRG/DSG Si786DG/DRG/DSG
Notes algebraic convention whereby most negative value minimum most positive maximum. Typical values DESIGN ONLY, guaranteed subject production testing. main switching outputs track reference voltage. Loading reference reduces main outputs slightly according closed-loop gain (AVCL) reference voltage load-regulation error. AVCL 3.3-V supply unity gain. AVCL supply 1.54. Since reference uses supply, line regulation error insignificant. Limits temperature grades unless otherwise noted.
Document Number: 70189 S-40807-Rev. 26-Apr-04
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Si786
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
Efficiency Output Current,
Efficiency Output Current,
SYNC Efficiency
Efficiency
0.001 0.01 Output Current
0.001 0.01 Output Current
Efficiency 3.3-V Output Current,
Efficiency 3.3-V Output Current,
Efficiency Efficiency SYNC
0.001 0.01 3.3-V Output Current
0.001 0.01 3.3-V Output Current
Quiescent Supply Current Supply Voltage
Standby Supply Current Supply Voltage
Quiescent Supply Current (mA)
High
Supply Voltage
Supply Voltage
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Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
Shutdown Supply Current Supply Voltage
Mimimum VOUT Differential
Minimum VOUT Differential Output Current
Output Still Regulating
Shutdown Supply Current
SHDN
Supply Voltage
0.001 0.01 Output Current
Switching Frequency Load Current
1000.0 SYNC (300 kHz) Switching Frequency (kHz) 100.0
10.0 Load Current (mA) 1000
Pulse-Skipping Waveforms
Pulse-Width Modulation Mode Waveforms
Output mV/div
V/div
V/div
Output mV/div
mS/div ILoad
ns/div Output Current
Document Number: 70189 S-40807-Rev. 26-Apr-04
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Si786
TYPICAL CHARACTERISTICS (25_C UNLESS NOTED)
Load-Transient Response
LOAD CURRENT
3.3-V Load-Transient Response
LOAD CURRENT
Output mV/div
3.3-V Output mV/div
mS/div
mS/div
Line-Transient Response, Rising
Line-Transient Response, Falling
Output mV/div
Output mV/div
VIN, V/div
VIN, V/div
mS/div ILOAD
mS/div ILOAD
3.3-V Line-Transient Response, Rising
3.3-V Line-Transient Response, Falling
3.3-V Output mV/div
3.3-V Output mV/div
VIN, V/div
VIN, V/div
mS/div ILOAD
mS/div ILOAD
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Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
DESCRIPTION ORDERING INFORMATION
SYNC SHDN
View
BST3 PGND BST5
SSOP-28
DESCRIPTION
Symbol
SYNC SHDN BST5 PGND BST3
Description
Current-sense input 3.3-V Buck controller-this pins over current threshold with respect FB3. Soft-start input Connect capacitor from GND. ON/OFF logic input disables 3.3-V Buck controller. Connect directly automatic turn-on. Comparator noninverting input, threshold 1.650 Comparator output Connect unused. Comparator noninverting input (see D1). External bias supply-voltage input comparators Comparator output. Sources from when high. Sinks when regardless input voltage. Comparator output (see Q2). Analog ground. 3.3-V reference output. Supplies external loads Oscillator control/synchronization input. Connect capacitor GND, 1-mF/mA output 0.22 minimum. external clock synchronization, rising edge starts cycle start. internal 200-kHz oscillator, connect GND. 300-kHz oscillator, connect REF. Shutdown logic input, active low. Connect automatic turn-on. supply will disabled shutdown allowing connection SHDN. ON/OFF logic input disables Buck Controller. Connect automatic turn-on. Soft-start control input Buck controller. Connect capacitor from GND. Current-sense input Buck controller-this pins over current threshold referenced FB3. Gate-drive output supply high-side n-channel MOSFET. Inductor connection supply. Boost capacitor connection supply. Gate-drive output supply rectifying n-channel MOSFET. Power Ground. Feedback input Buck controller. logic supply voltage internal circuitry-able source 5-mA external loads. remains with valid voltage Supply voltage input. Gate-drive output 3.3-V supply rectifying n-channel MOSFET. Boost capacitor connection 3.3-V supply. Inductor connection 3.3-V supply. Gate-drive output 3.3-V supply high-side n-channel MOSFET. Feedback input 3.3-V Buck controller.
Document Number: 70189 S-40807-Rev. 26-Apr-04
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Si786
ORDERING INFORMATION
Part Number
Si786CG Si786CG-T1 Si786CRG Si786CRG-T1 Si786CSG Si786CSG-T1 Si786LG Si786LG-T1 Si786LRG Si786LRG-T1 Si786LSG Si786LSG-T1 Si786DG Si786DG-T1 Si786DRG Si786DRG-T1 Si786DSG Si786DSG-T1 Si786DSG-T1-E3 Si786DRG-T1-E3 Si786DG-T1-E3 D-Grade -40_ 85_C Si786LSG-T1-E3 Si786LRG-T1-E3 Si786LG-T1-E3 L-Grade -10_ 90_C Si786CSG-T1-E3 Si786CRG-T1-E3 Si786CG-T1-E3 C-Grade 70_C
Lead (Pb)-Free Part Number
Temp Range
VOUT
3.45 3.45 3.45
Demo Board
Si786DB
Temp Range
70_C
Board Type
Surface Mount
DESCRIPTION OPERATION
Si786 dual step-down converter, which takes 5.5-V 30-V input supplies power controllers (see Figure These 3.3-V supplies optional 300-kHz 200-kHz internal oscillator, external sync signal. Amount output current limited external components, deliver greater than either supply. well these main Buck controllers, additional loads driven from micropower linear regulators, (VL) other (REF)-see Figure These supplies each rated deliver linear regulator circuits fall regulation, both Buck controllers shut down. voltage comparators with adjustable output voltages included Si786. They used gate drive load switching applications, where n-channel MOSFETs used. Logic level voltages generated well, instance serve interfacing (e.g. Power-good signal). 3.3-V Switching Supply 3.3-V supply regulated current-mode controller conjunction with several externals: n-channel MOSFETs, rectifier, inductor output capacitors (see Figure gate drive supplied needs greater than provided bootstrap circuit consisting 100-nF capacitor diode connected BST3
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low-side switching MOSFET connected increases efficiency reducing voltage across rectifier diode. value sense resistor series with inductor sets maximum current limit, disallow current overloads power-on short-circuit situations. soft-start feature Si786 capacitor programmable; functions constant current source external capacitor connected GND. Excess currents power-on avoided, power-supplies sequenced with different turn-on delay times selecting correct capacitor value.
Switching Supply supply regulated current-mode controller which nearly same 3.3-V output. dropout voltage across supply, shown schematic Figure (typ) voltage falls, nearing supply will lower well, until linear regulator output falls below undervoltage lockout threshold. Below this threshold, controller shut off. frequency both controllers when SYNC tied REF. Connecting SYNC either sets frequency kHz.
Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
3.3-V Switching Controllers Each controller Si786 identical with exception preset output voltages. controllers only share three functional blocks (see Figure oscillator, voltage reference (REF) logic supply (VL). 3.3-V controllers independently enabled with pins respectively. PWMs direct-summing type, without typical integrating error amplifier along with phase shift which side effect this type topology. Feedback compensation needed, long output capacitance requirements met, according Design Considerations section this data sheet. main comparator open loop device which comprised three comparators summing four signals: feedback voltage error signal, current sense signal, slope-compensation ramp voltage reference shown Figure This method control comes closer ideal maintaining output voltage cycle-by-cycle basis. When load demands high current levels, controller Soft-Start slowly bring 3.3-V supplies, connect capacitors from GND. Asserting starts 4-mA constant current source charge these capacitors voltage these pins ramps does current limit comparator threshold, increase duty cycle MOSFETs their maximum level. left low, respective capacitor discharged GND. Leaving pins open will cause either controller reach terminal over-current level within efficiency. low-side rectifier shut when inductor current drops zero. Shoot-through current result when both high-side rectifying MOSFETs turned same time. Break-before-make timing internal Si786 manages this potential problem. During time when neither MOSFET Schottky conducting, that body diode low-side MOSFET forced conduct. Synchronous rectification always active when Si786 powered-up, regardless operational mode. Gate-Driver Boost Synchronous Rectifiers Synchronous rectification replaces Schottky rectifier with MOSFET, which controlled increase efficiency circuit. When high-side MOSFET switched off, inductor will maintain current flow, inverting inductor's polarity. path current then becomes circuit made Schottky diode, inductor load, which will charge output capacitor. diode 0.5-V forward voltage drop, which contributes significant amount power loss, decreasing efficiency. low-side switch placed parallel with Schottky diode turned just after diode begins conduct. Because rDS(ON) MOSFET low, voltage drop will large diode, which increases
Document Number: 70189 S-40807-Rev. 26-Apr-04
full mode. Every cycle from oscillator asserts output latch drives gate high-side MOSFET period determined duty cycle (approximately VOUT/VIN 100%) frequency. high-side switch turns off, setting synchronous rectifier latch 60ns later, rectifier MOSFET turns low-side switch stays until start next clock cycle continuous mode, until inductor current becomes positive again discontinuous mode. over-current situations, where inductor current greater than 100-mV current-limit threshold, high-side latch reset high-side gate drive shut off. During low-current load requirements, inductor current will deliver 25-mV minimum current threshold. Minimum Current comparator signals enter pulse-skipping mode when threshold been reached. Pulse-skipping mode skips pulses reduce switching losses, losses which decrease efficiency most light load. Entering this mode causes minimum current comparator reset high-side latch beginning each oscillator cycle.
Soft start helps prevent current spikes turn-on allows separate supplies delayed using external programmability.
high-side n-channel drive supplied flying-capacitor boost circuit (see Figure capacitor takes charge from then connected from gate source high-side MOSFET provide gate enhancement. power-up, low-side MOSFET pulls down charges BST_ capacitor connected During second half oscillator cycle, controller drives gate high-side MOSFET internally connecting node BST_ DH_. This supplies voltage higher than battery voltage gate high-side MOSFET. Oscillations gates high-side MOSFET discontinuous mode natural occurrence caused network formed inductor stray capacitance pins. negative side BST_ capacitor connected node, ringing inductor translated through gate drive.
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Si786
SCHEMATIC DRAWINGS
INPUT 1N4148 1N4148 BST5
Si786
BST3
D1FS4
SHDN SYNC
PGND
D1FS4
(Note 0.01 ON/OFF ON/OFF SHUTDOWN SYNC
(Note 0.01 COMPARATOR SUPPLY INPUT COMPARATOR COMPARATOR
Note short, Kelvin-connected board traces placed very close another.
FIGURE Si786 Application Circuit
SHDN 3.3-V Reference Linear Regulator BST3
3.3-V Controller (See Figure
PGND STANDBY Controller (See Figure BST5
SYNC kHz/200 Oscillator
1.65 1.65
FIGURE Si786 Block Diagram
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Si786
REF, Internal Reference)
Summing Comparator BST_ Level Shift
Slope Comp
Minimum Current (Pulse-Skipping)
Current Limit ShootThrough Control
Synchronous Rectifier Control Level Shift
PGND
FIGURE Si786 Controller Block Diagram
Document Number: 70189 S-40807-Rev. 26-Apr-04
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Si786
BATTERY INPUT
BST_
Level Translator
FIGURE Boost Supply Gate Drivers
OPERATIONAL MODES
Mode Pulse-Skipping Mode When load requires less than maximum, Si786 enters mode which drives gate clock cycle skips majority remaining cycles. Pulse-skipping mode cuts down switching losses, dominant power consumer current levels. region between pulse-skipping mode mode, controller transition between modes, delivering spurts pulses. This cause current waveform look irregular, will overly affect ripple voltage. Even this transitional mode efficiency will stay high. Current Limit current through external resistor, constantly monitored protect against over-current. value resistor placed series with inductor. voltage across measured connecting between FB_. this voltage larger than high-side MOSFET drive shut down. Eliminating over-currents protects MOSFET, load power source. Typical values sense resistors with load will
3.3-V Buck controllers operate continuous-current mode when load demands more than approximately maximum current (see typical curves). duty cycle approximated Duty_Cycle VOUT/VIN
this mode, inductor current continuous; first half cycle, current slopes when high-side MOSFET conducts then, second half, slopes back down when inductor providing energy output capacitor load. current enters inductor first half-cycle, also continuing through load; hence, load receiving continuous current from inductor. using this method, output ripple minimized smaller form-factor inductors used. output capacitor's largest effect output ripple. typically under worst case condition under light load with higher input battery voltage.
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Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
Oscillator SYNC There ways Si786 oscillator frequency: using external SYNC signal, using internal oscillator. SYNC driven with external CMOS level signal with frequency from synchronize internal oscillator. Tying SYNC either sets frequency sets frequency kHz. Operation typically used minimize output passive component sizes. Slower switching speeds needed lower input voltages.
DESIGN CONSIDERATIONS
Inductor Design Three specifications required inductor design: inductance (L), peak inductor current (ILPEAK), coil resistance (RL). equation computing inductance
VIN(MAX)-VOUT VIN(MAX) IOUT (LIR) VOUT Output voltage (3.3 VIN(MAX) Maximum input voltage (V); Switching frequency, normally kHz; IOUT Maximum load current (A); Ratio inductor peak-to-peak current average load current, typically 0.3.
Where:
Internal linear regulator supplies power internal logic circuitry. regulator available external from able source 10-mF capacitor should connected between GND. increase efficiency, when switching supply voltage greater than internally switched over output switching supply linear regulator turned off. linear regulator provides power internal 3.3-V bandgap reference (REF). 3.3-V reference supply external load, connected REF. Between connect capacitor, 0.22 plus load current. switching outputs will vary with reference; therefore, placing load will cause main outputs decrease slightly, within specified regulation tolerance. supplies stay long greater than even switching supplies enabled. This feature necessary when using micropower regulators keep memory alive during shutdown. Both linear regulators connected their respective switching supply outputs. example, would tied output This will keep main supplies standby mode, provided that each load current shutdown larger than
When higher, smaller inductance values acceptable, expense increased ripple higher losses. peak inductor current (ILPEAK) equal steady-state load current (IOUT) plus half peak-to-peak current (ILPP). Typically, designer will select inductor current steady-state current, which gives ILPEAK equal 1.15 times IOUT equation computing peak inductor current
ILPEAK IOUT VOUT VIN(MAX)-V (2)(f)(L) VIN(MAX)
Output Capacitors output capacitors determine loop stability ripple voltage output. order maintain stability, minimum capacitance maximum requirements must according following equations:
and, VOUT VREF Output filter capacitance VREF Reference voltage, VOUT Output voltage, Sense resistor (W); GBWP Gain-bandwidth product, kHz; ESRCF Output filter capacitor (W).
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VREF VOUT (2)(p)(GBWP)
ESRCF
Fault Protection
Where:
switching controllers well comparators shut down when linear regulators drops below nominal value; that shut down will occur when
Document Number: 70189 S-40807-Rev. 26-Apr-04
Si786
Both minimum capacitance maximum requirements must met. order ESR, capacitance value three times greater than required minimum necessary. equation output ripple continuous current mode
VOUT(RPL) ILPP(MAX) ESRCF
Lower Voltage Input
application circuit shown here easily modified work with 5.5-V 12-V input voltages. Oscillation frequency should increase output capacitance output maintain stable performance load current. Operation 3.3-V supply will affected this reduced input voltage.
equations capacitive resistive components ripple pulse-skipping mode are:
VOUT(RPL)(C) 10-4 VOUT VIN-V
VOUT(RPL)(R)
(0.02) ESRCF
total ripple, VOUT(RPL) approximated follows: VOUT(RPL)(R) VOUT(RPL)(C), then VOUT(RPL) VOUT(RPL)(C), otherwise, VOUT(RPL) VOUT(RPL)(C) VOUT(RPL)(R).
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Document Number: 70189 S-40807-Rev. 26-Apr-04

Dual-Output Power-Supply Controller Fixed 3.3-V Step-down Convert

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