1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter

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1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter

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19-1381; 7/98
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter
0.87V Guaranteed Start-Up Efficiency Built-In Synchronous Rectifier external diode) Ultra-Small µMAX Package, 1.1mm High 37µA Quiescent Current (85µA from 1.5V battery) Logic-Controlled Shutdown Power-Fail Detector Dual ModeOutput: Fixed 3.3V Adjustable 5.5V 45mA Output Current 3.3V 1-Cell Input 90mA Output Current 3.3V 2-Cell Input Inductor-Damping Switch Suppresses
MAX1678
MAX1678 high-efficiency, low-voltage, synchronous-rectified, step-up DC-DC converter intended devices powered 3-cell alkaline, NiMH, NiCd batteries 1-cell lithium battery. guarantees 0.87V start-up voltage features 37µA quiescent supply current. device includes N-channel MOSFET power switch, synchronous rectifier that acts catch diode, reference, pulse-frequency-modulation (PFM) control circuitry, circuitry reduce inductor ringing-all ultra-small, 1.1mm-high µMAX package. output voltage preset 3.3V adjusted from +5.5V using only resistors. Efficiencies achieved loads 50mA. device also features independent undervoltage comparator (PFI/PFO) logic-controlled shutdown mode.
Applications
Pagers Remote Controls Pointing Devices Personal Medical Monitors Single-Cell Battery-Powered Devices
PART MAX1678EUA
Ordering Information
TEMP. RANGE -40°C +85°C PIN-PACKAGE µMAX
Note: order these devices shipped tape-and-reel, part number.
Typical Operating Circuit
Configuration
INPUT 0.87V VOUT
OUTPUT 3.3V
VIEW
MAX1678
BATT LOW-BATTERY DETECTOR INPUT SHDN LOW-BATTERY DETECTOR OUTPUT BATT SHDN
MAX1678
µMAX
Dual Mode trademark Maxim Integrated Products.
Maxim Integrated Products
free samples latest literature: http://www.maxim-ic.com, phone 1-800-998-8800. small orders, phone 408-737-7600 ext. 3468.
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
ABSOLUTE MAXIMUM RATINGS
BATT, OUT,LX, SHDN .-0.3V +6.0V OUT, Current.1A PFI, .-0.3V (VOUT 0.3V) Reverse Battery Current +25°C) (Note .220mA Continuous Power Dissipation +70°C) µMAX (derate 4.1mW/°C above +70°C) .330mW Operating Temperature Range .-40°C +85°C Junction Temperature .+150°C Storage Temperature Range .-65°C +165°C Lead Temperature (soldering, 10sec) .+300°C
Note reverse battery current measured from Typical Operating Circuit's input terminal when battery connected backward. reverse current 220mA will exceed package dissipation limits but, left extended time (more than minutes), degrade performance.
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VBATT SHDN 1.3V, ILOAD GND, +85°C, unless otherwise noted. Typical values +25°C.) PARAMETER Minimum Operating Input Voltage Maximum Operating Input Voltage Start-Up Voltage (Note Start-Up Voltage Tempco Output Voltage (Fixed Mode) Output Voltage Range (Adjustable Mode) Voltage N-Channel On-Resistance P-Channel On-Resistance P-Channel Catch Diode Voltage Maximum Peak Current On-Time Constant Quiescent Current into Quiescent Current into BATT Shutdown Current into Shutdown Current into BATT Efficiency Input Current Trip Voltage Input Current Output Voltage Leakage Current SHDN Input Voltage SHDN Input High Voltage SHDN Input Current SHDN BATT VBATT VIL,PFI ILX(MAX) IQ,OUT IQ,BATT ISHDN,OUT ISHDN,BATT VOUT 3.5V VBATT ILOAD 20mA, VBATT 2.5V (Figure 1.3V Falling hysteresis VPFI 650mV VPFI VOUT 3.3V, ISINK VPFI 650mV, VPFO 0.9V VBATT 3.3V (tON VBATT) VOUT 3.5V 5.60 VOUT 0.1V External feedback External feedback VOUT 3.3V VOUT 3.3V IDIODE 100mA, P-channel switch 3.16 1.19 1.23 0.04 0.01 11.2 SYMBOL VBATT(MIN) VBATT(MAX) +25°C 0.87 3.44 1.26 CONDITIONS UNITS mV/°C V-µs
VBATT
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS
(VBATT SHDN 1.3V, ILOAD GND, -40°C +85°C, unless otherwise noted.) (Note PARAMETER Maximum Operating Input Voltage Output Voltage (Fixed Mode) Output Voltage Range (Adjustable Mode) Voltage N-Channel On-Resistance P-Channel On-Resistance On-Time Constant Quiescent Current into Quiescent Current into BATT Shutdown Current into Shutdown Current into BATT Input Current Trip Voltage Input Current Output Voltage Leakage Current SHDN Input Voltage SHDN Input High Voltage SHDN Input Current SHDN BATT VBATT VIL,PFI IQ,OUT IQ,BATT ISHDN,OUT ISHDN,BATT VOUT 3.5V VBATT 1.3V Falling hysteresis VPFI 650mV VPFI VOUT 3.3V, ISINK VPFI 650mV, VPFO SYMBOL VBATT(MAX) VOUT 0.1V External feedback External feedback VOUT 3.3V VOUT 3.3V 0.9V VBATT 3.3V (tON VBATT) VOUT 3.5V 5.60 3.12 1.17 CONDITIONS 3.48 1.28 11.2 VBATT UNITS V-µs
MAX1678
Note Start-up guaranteed correlation measurements device parameters (i.e., switch on-resistance, on-time, off-time, output voltage trip point). Note Specifications -40°C guaranteed design production tested.
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
Typical Operating Characteristics
(Circuit Figure (Fixed Mode, 3.3V) Figure (Adjustable Mode), +25°C, unless otherwise noted.)
EFFICIENCY LOAD CURRENT (VOUT 2.4V, 22µH)
MAX1678-01
EFFICIENCY LOAD CURRENT (VOUT 2.4V, SUMIDA 47µH)
MAX1678-02
EFFICIENCY LOAD CURRENT (VOUT 2.4V, 47µH)
2.0V 1.5V
MAX1678-03
EFFICIENCY 0.01 22µH SUMIDA CD43-220 200k, 200k 0.85V 1.2V 1.5V 2.0V
EFFICIENCY 1.2V 0.85V 1.5V 2.0V
0.01
EFFICIENCY
0.85V 1.2V
47µH SUMIDA CD43-470 200k, 200k
0.01
47µH NLC453232T-470K 200k, 200k
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY LOAD CURRENT (VOUT 3.3V, 22µH)
MAX1678-04
EFFICIENCY LOAD CURRENT (VOUT 3.3V, SUMIDA 47µH)
MAX1678-05
EFFICIENCY LOAD CURRENT (VOUT 3.3V, 47µH)
2.5V 1.5V 2.0V
MAX1678-06 MAX1678-09
EFFICIENCY 0.01 22µH SUMIDA CD43-220 0.85V 1.2V 2.5V 2.0V 1.5V
EFFICIENCY 2.5V
2.0V
0.01
0.85V 1.5V
EFFICIENCY
1.2V
0.85V 1.2V
47µH SUMIDA CD43-470
0.01
47µH NLC453232T-470K
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
EFFICIENCY LOAD CURRENT (VOUT 5.0V, 22µH)
MAX1678-07
EFFICIENCY LOAD CURRENT (VOUT 5.0V, SUMIDA 47µH)
EFFICIENCY 4.5V 3.0V 2.0V 1.2V 0.85V EFFICIENCY
MAX1678-08
EFFICIENCY LOAD CURRENT (VOUT 5.0V, 47µH)
1.2V 0.85V 2.0V 4.5V 3.0V
EFFICIENCY 0.01 22µH SUMIDA CD43-220 619k, 200k 0.85V 1.2V 4.5V 3.0V 2.0V
0.01
47µH SUMIDA CD43-470 619k, 200k
0.01
47µH NLC453232-470K 619k, 200k
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit Figure (Fixed Mode, 3.3V) Figure (Adjustable Mode), +25°C, unless otherwise noted.)
NO-LOAD BATTERY CURRENT INPUT VOLTAGE
MAX1678-11
MAX1678
EFFICIENCY WITH DIFFERENT INDUCTORS
EFFICIENCY
DS1608C-473 CD43-470 22µH NLC453232T-220K 47µH NLC453232T-470K
BATT QUIESCENT CURRENT TEMPERATURE
QUIESCENT CURRENT (µA) TEMPERATURE (°C) IBATT VBATT 1.3V VOUT 3.6V
MAX1678-12
NO-LOAD BATTERY CURRENT (µA)
VBATT 1.2V VOUT 3.3V ILOAD 20mA
MAX1678-10
1000 VOUT 5.0V VOUT 3.0V
IOUT
DT1608C-223
LQH4N470K
CD43-220
LQH3C470K
47µH
22µH
47µH
22µH
47µH
47µH
VOUT 2.4V 47µH SUMIDA CD43-470 INPUT VOLTAGE
COILCRAFT SUMIDA
MURATA
SHUTDOWN BATTERY CURRENT INPUT VOLTAGE
MAX1678-13
ON-TIME CONSTANT TEMPERATURE
MAX1678-14
MINIMUM START-UP INPUT VOLTAGE LOAD CURRENT
47µH SUMIDA CD43-470 3.3V FIXED MODE WITHOUT DIODE
MAX1678-15
SHUTDOWN BATTERY CURRENT (µA) INPUT VOLTAGE 3.3V FIXED MODE 47µH SUMIDA CD43-470
VBATT 1.3V ON-TIME CONSTANT (V-µs)
START-UP INPUT VOLTAGE
WITH EXTERNAL SCHOTTKY DIODE (FIGURE
TEMPERATURE (°C)
LOAD CURRENT (mA)
MAXIMUM LOAD CURRENT INPUT VOLTAGE 22µH)
MAX1678-16
MAXIMUM LOAD CURRENT INPUT VOLTAGE SUMIDA 47µH)
MAX1678-17
MAXIMUM LOAD CURRENT INPUT VOLTAGE 47µH)
47µH NLC453232T-470K
MAX1678-18
MAXIMUM LOAD CURRENT (mA) VOUT 3.3V VOUT 5.0V 22µH SUMIDA CD43-220 VOUT 2.4V
MAXIMUM LOAD CURRENT (mA) VOUT 2.4V VOUT 5.0V 47µH SUMIDA CD43-470
MAXIMUM LOAD CURRENT (mA) VOUT 2.4V VOUT 5.0V VOUT 3.3V
VOUT 3.3V
INPUT VOLTAGE
INPUT VOLTAGE
INPUT VOLTAGE
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
Typical Operating Characteristics (continued)
(Circuit Figure (Fixed Mode, 3.3V) Figure (Adjustable Mode), +25°C, unless otherwise noted.)
SWITCHING WAVEFORM
MAX1678-19
LOAD-TRANSIENT RESPONSE
MAX1678-20
5µs/div VOUT 3.3V, VBATT 1.2V, ILOAD 10mA, COUT 10µF, SUMIDA CD43-470 2V/div VOUT, 50mV/div COUPLED INDUCTOR CURRENT, 100mA/div 100µs/div VOUT 3.3V, VBATT 1.2V, COUT 10µF, SUMIDA CD43-470, VOUT, 50mV/div, COUPLED INDUCTOR CURRENT, LOAD, 12mA 100mA/div
LINE-TRANSIENT RESPONSE
MAX1678-21
POWER-UP RESPONSE
MAX1678-22
200µs/div VOUT 3.3V, VBATT 1.2V, ILOAD 10mA, COUT 10µF, SUMIDA CD43-470 VOUT, 50mV/div, COUPLED VIN, 1V/div, 1.2V 2.2V
100µs/div VOUT 3.3V, VBATT 1.2V, ILOAD 10mA, COUT 10µF, SUMIDA CD43-470 INDUCTOR CURRENT, 100mA/div VOUT, 1V/div SHDN, 5V/div
Description
NAME BATT SHDN Battery-Power Input Power-Fail Input. When voltage below 614mV, sinks current. Open-Drain Power-Fail Output. sinks current when below 614mV. Active-Low Shutdown. Connect SHDN BATT normal operation. Dual-Mode Feedback Input. Connect fixed-output operation (3.3V). Connect feedback-resistor network adjustable output voltage operation 5.5V). regulates 1.23V. Ground N-Channel MOSFET Switch Drain P-Channel Synchronous-Rectifier Drain Power Output Power Input (bootstrapped). feedback input 3.3V operation. Connect filter capacitor close OUT. FUNCTION
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
BACKUP tOFF TIMER ZERO-CROSSING DETECTION
BATT DAMPING SWITCH K/VBATT DAMP TOFF PDRV NDRV
0.5REF
CONTROL LOGIC
MAX1678
RFRDY 1.23V
0.5REF
START-UP OSCILLATOR
SHDN START-UP COMPARATOR 1.7V
Figure Functional Diagram
Detailed Description
MAX1678 consists internal N-channel MOSFET power switch, built-in synchronous rectifier that acts catch diode, reference, control circuitry, inductor damping switch (Figure device optimized applications that powered 3-cell alkaline, NiMH, NiCd batteries, 1-cell lithium battery such pagers, remote controls, battery-powered instruments. They designed meet specific demands operating states characteristic such systems: Primary battery good load active: this state load draws tens milliamperes MAX1678 typically offers efficiency.
Primary battery good load sleeping: this state load draws hundreds microamperes DC-DC converter draws very quiescent current. Many applications maintain load this state most time. Primary battery dead DC-DC converter shut down: this state load sleeping supplied backup battery, MAX1678 draws 0.1µA current from pin. Primary backup battery dead: DC-DC converter restart from this condition.
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
Operating Principle
MAX1678 employs proprietary constant-peakcurrent control scheme that combines ultra-low quiescent current traditional pulse-skipping converters with high-load efficiency. When error comparator detects that output voltage low, turns internal N-channel MOSFET switch internally calculated on-time (Figure During on-time, current ramps inductor, storing energy magnetic field. When MOSFET turns during second half each cycle, magnetic field collapses, causing inductor voltage force current through synchronous rectifier, transferring stored energy output filter capacitor load. output filter capacitor stores charge while current from inductor high, then holds output voltage until second half next switching cycle, smoothing power flow load. ideal on-time N-channel MOSFET changes function input voltage. on-time determined follows: VBATT
VOUT VBATT VBATT (DEAD TIME) TIME)
VBATT
VOUT VBATT IPEAK
IPEAK
TIME) (DEAD TIME) tOFF DEAD TIME
Figure Switching Waveforms
VOUT COUT
where typically 8V-µs. peak inductor current (assuming lossless circuit) calculated from following equation: IPEAK P-channel MOSFET (synchronous rectifier) turns when N-channel MOSFET turns off. circuit operates edge discontinuous conduction; therefore, P-channel synchronous rectifier turns immediately after inductor current ramps zero. During dead time after P-switch been turned off, damping switch connects BATT. This suppresses noise ringing inductor parasitic capacitance node (see Damping Switch section). error comparator starts another cycle when VOUT falls below regulation threshold. With this control scheme, MAX1678 maintains high efficiency over wide range loads input/output voltages while minimizing switching noise.
MAX1678
PDRV TIMING CIRCUIT NDRV START-UP OSCILLATOR
Figure External Schottky Diode Improve Start-Up with Heavy Load
Start-Up Operation
MAX1678 contains low-voltage start-up oscillator (Figure This oscillator pumps output voltage approximately 1.7V, level which main DCDC converter operate. 150kHz fixed-frequency oscillator powered from BATT input drives switch. During start-up, P-channel synchronous
rectifier remains body diode external diode, desired) used output rectifier. minimum start-up voltage function load current (see Typical Operating Characteristics). normal operation, when voltage exceeds 1.7V, DCDC converter powered from (bootstrapped) main control circuitry enabled. Once started, output maintain load battery voltage decreases below start-up voltage. improve start-up capability with heavy loads, Schottky diode parallel with P-channel synchronous rectifier (from OUT) shown Figure (see Typical Operating Characteristics).
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter
Pulling SHDN places MAX1678 shutdown mode (ISHDN typical). shutdown, internal switching MOSFET turns off, goes high impedance, synchronous rectifier turns prevent flow reverse current from output back input. However, there still forward current path through synchronous-rectifier body diode from input output. Thus, shutdown, output remains diode drop below battery voltage (VBATT). disable shutdown feature, connect SHDN logic input) BATT OUT.
Shutdown Mode
MAX1678
VOUT
MAX1678
PDRV BATT
TIMING CIRCUIT DAMP
DAMPING SWITCH
Reverse-Battery Protection
MAX1678 sustain/survive battery reversal package power-dissipation limit. internal resistor series with diode limits reverse current less than 220mA, preventing damage. Prolonged operation above 220mA reverse-battery current degrade device's performance.
NDRV
Figure Simplified Diagram Damping Switch
Power-Fail Comparator
MAX1678 on-chip comparator power-fail detection. This comparator detect loss power input output (Figures voltage power-fail input (PFI) falls below 614mV, output sinks current GND. Hysteresis power-fail monitor threshold resistors, using following equation: VPFI where desired threshold power-fail detector, VPFI 614mV threshold powerfail comparator. Since leakage 10nA max, select feedback resistor 100k range.
2µs/div
1V/div
VBATT 2.5V VOUT 3.3V 47µH
Figure Ringing Without Damping Switch (example only)
Damping Switch
MAX1678 designed with internal damping switch minimize ringing node. damping switch (Figure connects node BATT, effectively depleting inductor's remaining energy. When energy inductor insufficient supply current output, capacitance inductance form resonant circuit that causes ringing. damping switch supplies path quickly dissipate this energy, suppressing ringing This does reduce output ripple, does reduce EMI. Figures show node voltage waveform without with damping switch.
1V/div
VBATT 1.8V VOUT 3.3V 47µH 2µs/div
Figure Ringing With Damping Switch
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
Applications Information
Output Voltage Selection
MAX1678 operates with fixed 3.3V adjustable output. select fixed-voltage operation, connect (Figure adjustable output between 5.5V, connect resistor voltage-divider between (Figure regulates 1.23V. Since leakage 10nA max, select feedback resistor 100k range. given VREF where VREF 1.23V. IOUT(MAX) BATT VOUT
where empirical factor that takes into account losses MAX1678 internal switches inductor resistance. V-µs factor that governs inductor charge time. Nominally, 8V-µs. should further reduced each inductor resistance. inductor's saturation-current rating must exceed worst-case peak current limit MAX1678's timing algorithm: KMAX IPEAK where 11.2V-µs. usually acceptable exceed most coil saturation-current ratings with effects; however, maximum recommended IPEAK MAX1678 internal switches 550mA, inductor values below 22µH recommended. optimum efficiency, inductor series resistance should less than 150mV/IPEAK. Table lists suggested inductors suppliers.
Maximum Output Current Inductor Selection
MAX1678 designed work well with 47µH inductor most low-power applications. 47µH sufficiently value allow small surfacemount coil, large enough maintain ripple. Typical Operating Characteristics section shows performance curves with several 47µH 22µH coils. inductance values supply higher output current also increase ripple reduce efficiency. Note that values below 22µH recommended MAX1678 switch limitations. Higher inductor values reduce peak inductor current (and consequent ripple noise) improve efficiency, also limit output current. relationship between current inductor value approximately:
Table Suggested Inductors Suppliers
Coilcraft Murata Sumida INDUCTOR DS1608C-223, DS1608C-473 LQH4N470K, LQH3C470K CD43-220, CD43-470 NLC453232T-220K, NLC453232T-470K
47µH
PHONE (847) 639-6400 (814) 237-1431 (847) 956-0666 (847) 390-4373
INPUT 0.87V VOUT 10µF
47µH, 200mA
INPUT 0.87V VOUT 10µF 3.3VOUT 10µF
BATT
BATT
VOUT 5.5V
MAX1678
SHDN
MAX1678
SHDN
Figure 3.3V Standard Application Circuit
Figure Adjustable Output Circuit
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter
Capacitor Selection
Choose input output capacitors service input output peak currents with acceptable voltage ripple. Capacitor major contributor output ripple (usually more than 60%). 10µF, ceramic output filter capacitor typically provides 50mV output ripple when stepping from 1.3V 3.3V 20mA. input output voltage differences (i.e., cells 3.3V) require higher capacitor values (10µF 47µF). input filter capacitor (CIN) also reduces peak currents drawn from battery improves efficiency. Low-ESR capacitors recommended. Ceramic capacitors have lowest ESR, low-ESR tantalums represent good balance between cost performance. Low-ESR aluminum electrolytic capacitors tolerable, standard aluminum electrolytic capacitors should avoided. Capacitance variation over temperature need taken into consideration best performance applications with wide operating temperature ranges. Table lists suggested capacitors suppliers. Follow sound circuit-board layout grounding rules (see Board Layout Grounding section).
MAX1678
Board Layout Grounding
High switching frequencies large peak currents make board layout important part design. Poor design result excessive feedback paths voltage gradients ground plane. Both these factors result instability regulation errors. must bypassed directly GND, close possible (within inches 5mm). Place power components-such MAX1678, inductor, input filter capacitor, output filter capacitor-as close together possible. Keep their traces short, direct, wide 1.25mm), place their ground pins close together star-ground configuration. Keep extra copper board integrate into ground pseudo-ground plane. multilayer boards, route star ground using component-side copper fill, then connect internal ground plane using vias. Place external voltage-feedback network very close (within inches 5mm). Noisy traces, such from pin, should kept away from voltage-feedback network separated from using grounded copper. MAX1678 evaluation manual shows example board layout, which includes pseudo-ground plane.
Minimizing Noise Voltage Ripple
output voltage ripple minimized following these simple design rules: Place DC-DC converter digital circuitry opposite corner board from sensitive analog input stages. closed-core inductor, such toroid shielded bobbin, minimize fringe magnetic fields. Choose largest inductor value that satisfies load requirement, minimize peak switching current resulting ripple noise. low-ESR input output filter capacitors.
Table Recommended Surface-Mount Capacitor Manufacturers
VALUE (µF) TAJ, TPS-series tantalum ceramic ceramic Taiyo Yuden 803-946-0690 408-573-4150 803-946-0690 847-390-4373 DESCRIPTION 595D-series tantalum MANUFACTURER Sprague PHONE 603-224-1961
1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter MAX1678
_Chip Information
TRANSISTOR COUNT:
Package Information
8LUMAXD.EPS

1-Cell 2-Cell, Low-Noise, High-Efficiency, Step-Up DC-DC Converter

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