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19-1198; Rev 0; 4/97
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
_______________General Description
The MAX1705/MAX1706 are high-efficiency, low-noise, step-up DC-DC converters with an auxiliary linearregulator output. These devices are intended for use in battery-powered wireless applications. They use a synchronous rectifier pulse-width-modulation (PWM) boost topology to generate 2.5V to 5.5V outputs from battery inputs, such as 1 to 3 NiCd/NiMH cells or 1 Li-Ion cell. The MAX1705 has an internal 1A N-channel MOSFET switch. The MAX1706 has a 0.5A switch. Both devices also have a built-in low-dropout linear regulator that delivers up to 200mA. With an internal synchronous rectifier, the MAX1705/ MAX1706 deliver 5% better efficiency than similar nonsynchronous converters. They also feature a pulsefrequency-modulation (PFM) standby mode to improve efficiency at light loads, and a 1A shutdown mode. An efficiency-enhancing track mode reduces the step-up DC-DC converter output to 300mV above the linear-regulator output. Both devices come in a 16-pin QSOP package, which occupies the same space as an 8-pin SO. Other features include two shutdown-control inputs for push-on/push-off control, and an uncommitted comparator for use as a voltage monitor.
NUAL KIT MA UATION BLE EVAL AVAILA
____________________________Features
o Up to 96% Efficiency o 1.1VIN Guaranteed Start-Up o Up to 850mA Output (MAX1705) o Step-Up Output (2.5V to 5.5V adjustable) o Linear Regulator (1.25V to 5.0V adjustable) o PWM/PFM Synchronous-Rectified Topology o 300kHz PWM Mode or Synchronizable o 1A Shutdown Mode o Voltage Monitor o Pushbutton On/Off Control
MAX1705/MAX1706
______________Ordering Information
PART MAX1705C/D TEMP. RANGE 0C to +70C PIN-PACKAGE Dice*
16 QSOP -40C to +85C MAX1705EEE Dice* MAX1706C/D 0C to +70C 16 QSOP MAX1706EEE -40C to +85C *Dice are tested at TA = +25C, DC parameters only.
________________________Applications
Digital Cordless Phones Personal Communicators Palmtop Computers Hand-Held Instruments PCS Phones Wireless Handsets Two-Way Pagers
__________Typical Operating Circuit
INPUT 0.7V TO 5.5V
__________________Pin Configuration
LOW-BATTERY DETECTION
LX LBP POUT OUT
STEP-UP OUTPUT
TOP VIEW
LBP 1 LBN 2 REF 3 TRACK 4 GND 5 OUT 6 FB 7 FBLDO 8
16 POUT
LBO
15 ONA 14 ONB
MAX1705 MAX1706
FB
ON/OFF CONTROL HIGH EFFICIENCY LOW NOISE
ONA ONB CLK/SEL TRACK LBN REF LDO FBLDO GND PGND LINEAR REGULATOR OUTPUT
MAX1705 MAX1706
13 LX 12 PGND 11 CLK/SEL 10 LBO 9 LDO
QSOP
________________________________________________________________ Maxim Integrated Products
1
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, FBLDO, OUT, POUT to GND...................-0.3V to 6V PGND to GND.....................................................................0.3V POUT to OUT ......................................................................0.3V LX to PGND ............................................-0.3V to (VPOUT + 0.3V) CLK/SEL, REF, FB, TRACK, LDO, LBN, LBP, LBO to GND.......................-0.3V to (VOUT + 0.3V) LDO Short Circuit .......................................................Continuous Continuous Power Dissipation (TA = +70C) QSOP (derate 8.70mW/C above +70C) ...................696mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22F), LX = open, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC-DC CONVERTER Minimum Start-Up Voltage Minimum Operating Battery Voltage FB Regulation Voltage FB Input Current OUT Adjust Range Load Regulation MAX1705, 0A ILX 0.5A; MAX1706, 0A ILX 0.25A; CLK/SEL = OUT TRACK = VLDO > 2.3V fLX VPOUT = VOUT = 1.5V (Note 2) IOUT IOUT ONA = GND, ONB = OUT, measure IOUT CLK/SEL = GND, VFB = VFBLDO = 1.5V, no load VFB = VFBLDO = 1.5V, no load IOUT CLK/SEL = OUT FB = GND (LX switching) IREF = 0A -1A < IREF < 50A 2.5V < VOUT < 5.5V 1.238 2.1 1.250 4 0.2 1.262 15 5 mA V mV mV VLDO + 0.2 40 2.00 TA = +25C, ILOAD < 1mA, Figure 2 (Note 1) CLK/SEL = OUT VFB = 1.5V 2.5 0.65 VLDO + 0.3 150 2.15 1 100 180 1.219 0.9 0.7 1.233 0.01 1.247 50 5.5 1.25 VLDO + 0.4 300 2.30 20 190 360 1.1 V V V nA V % SYMBOL CONDITIONS MIN TYP MAX UNITS
OUT Voltage in Track Mode Frequency in Start-Up Mode Start-Up to Normal Mode Transition Voltage Supply Current in Shutdown Supply Current in Low-Power Mode Supply Current in Low-Noise Mode REFERENCE Reference Output Voltage Reference Load Regulation Reference Supply Regulation
V kHz V A A A
2
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22F), LX = open, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC-DC SWITCHES POUT Leakage Current LX Leakage Current Switch On-Resistance VLX = 0V, V ONB = VOUT = 5.5V VLX = 0V, V ONB = VOUT = 5.5V N-channel, ILX = 100mA P-channel, ILX = 100mA CLK/SEL = OUT N-Channel MOSFET Current Limit ILIM CLK/SEL = GND P-Channel SynchronousRectifier Turn-Off Current LINEAR REGULATOR FBLDO Regulation Voltage FBLDO Input Current LDO Adjust Range Short-Circuit Current Limit Dropout Resistance Load Regulation Line Regulation AC Power-Supply Rejection Thermal Shutdown LOW-BATTERY COMPARATOR LBN, LBP Offset LBN, LBP Hysteresis LBN, LBP Common-Mode Input Range LBN, LBP Input Current LBO Output Low Voltage LBO High Leakage CONTROL INPUTS Input Low Level Input High Level Input Leakage Current (CLK/SEL, ONA, ONB, TRACK) 1.2V < VOUT < 5.5V, ONA, ONB (Note 3) VOUT = 2.5V, CLK/SEL, TRACK 1.2V < VOUT < 5.5V, ONA, ONB (Note 3) VOUT = 5.5V, CLK/SEL, TRACK 0.8VOUT 0.8VOUT 1 0.2VOUT 0.2VOUT V V A LBP falling LBP rising VLBN = 0.5V and 1.5V (at least one input must be within this range) VLBN = VLBP = 1V ISINK = 1mA, VOUT = 2.5V, LBP = GND, LBN = OUT VLBO = VOUT = 5V 0.5 0.01 -5 16 1.5 50 0.4 1 5 mV mV V nA V A FBLDO = GND VFBLDO = 1V, ILDO = 200mA 10A < ILDO < 200mA, FBLDO = LDO 2.5V < VOUT < 5.5V, FBLDO = LDO, ILDO = 1mA f = 300kHz Hysteresis approximately 10C FBLDO = LDO, ILOAD = 1mA VFBLDO = 1.5V 1.25 220 300 0.5 0.4 0.1 38 155 1.238 1.250 0.01 1.262 50 5.0 500 1.2 1.2 0.5 V nA V mA % % dB C CLK/SEL = GND MAX1705 MAX1706 MAX1705 MAX1706 1000 550 250 250 20 CLK/SEL = GND CLK/SEL = OUT 0.1 0.1 0.23 0.16 0.27 1280 750 435 435 70 20 20 0.45 0.28 0.50 1550 950 550 550 120 mA mA A A SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1705/MAX1706
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22F), LX = open, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Internal Oscillator Frequency External Oscillator Synchronization Range Oscillator Maximum Duty Cycle Minimum CLK/SEL Pulse Maximum CLK/SEL Rise/Fall Time SYMBOL CONDITIONS CLK/SEL = OUT MIN 260 200 80 86 200 100 TYP 300 MAX 340 400 90 UNITS kHz kHz % ns ns
ELECTRICAL CHARACTERISTICS
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22F), LX = open, TA = -40C to +85C, unless otherwise noted, Note 4.) PARAMETER DC-DC CONVERTER FB Regulation Voltage OUT Voltage in Track Mode Start-Up to Normal Mode Transition Voltage Supply Current in Shutdown Supply Current in Low-Power Mode Supply Current in Low-Noise Mode REFERENCE Reference Output Voltage DC-DC CONVERTER Switch On-Resistance N-channel, ILX = 100mA P-channel, ILX = 100mA CLK/SEL = OUT N-Channel MOSFET Current Limit ILIM CLK/SEL = 0V P-Channel SynchronousRectifier Turn-Off Current CLK/SEL = 0V CLK/SEL = 0V CLK/SEL = OUT CLK/SEL = OUT MAX1705 MAX1706 MAX1705 MAX1706 1000 550 250 250 20 0.45 0.28 0.50 1700 950 570 570 120 mA mA IREF = 0A 1.235 1.265 V IOUT IOUT IOUT ONA = 0V, ONB = OUT, measure IOUT CLK/SEL = 0V, FB = FBLDO = 1.5V, no load CLK/SEL = OUT, VFB = VFBLDO = 1.5V, no load SYMBOL CONDITIONS CLK/SEL = OUT TRACK = OUT, VLDO > 2.3V MIN 1.215 VLDO + 0.2 2.0 TYP MAX 1.251 VLDO + 0.4 2.3 20 190 360 UNITS V V V A A A
4
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
ELECTRICAL CHARACTERISTICS (continued)
(VOUT = VPOUT = VLBP = 3.6V, CLK/SEL = FB = LBN = LBO = ONA = ONB = TRACK = GND, REF = open (bypassed with 0.22F), LX = open, TA = -40C to +85C, unless otherwise noted, Note 4.) PARAMETER LINEAR REGULATOR FBLDO Regulation Voltage FBLDO Input Current Short-Circuit Current Limit Dropout Resistance LOW-BATTERY COMPARATOR LBN, LBP Offset LBN, LBP Common-Mode Input Range LBO High Leakage CONTROL INPUTS Input Low Level Input High Level Internal Oscillator Frequency External Oscillator Synchronization Range Note 1: Note 2: Note 3: Note 4: 1.2V < VOUT < 5.5V, ONA, ONB (Note 2) VOUT = 2.5V, CLK/SEL, TRACK 1.2V < VOUT < 5.5V, ONA, ONB (Note 2) VOUT = 5.5V, CLK/SEL, TRACK CLK/SEL = OUT 0.85VOUT 0.85VOUT 260 200 340 400 0.15VOUT 0.15VOUT V V kHz kHz LBP falling LBN = 0.5V and 1.5V (at least one input must be within this range) LBO = OUT = 5V -5 0.5 5 1.5 1 mV V A FBLDO = LDO, ILOAD = 1mA VFBLDO = 1.5V FBLDO = LDO = GND VFBLDO = 1V, ILDO = 200mA 220 1.233 0.01 1.268 50 600 1.2 V nA mA SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX1705/MAX1706
Once the output is in regulation, the MAX1705/MAX1706 operate down to a 0.7V input voltage. The device is in start-up mode when VOUT is below this value (see Low-Voltage Start-Up Oscillator section). ONA and ONB inputs have a hysteresis of approximately 0.15VOUT. Specifications to -40C to are guaranteed by design, not production tested.
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
__________________________________________Typical Operating Characteristics
(Circuit of Figure 2, TA = +25C, unless otherwise noted.)
MAX1705 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V)
MAX1705/6 TOC01
MAX1705 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V)
MAX1705/6 TOC02
MAX1705 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
900 MAXIMUM OUTPUT CURRENT (mA) 800 700 600 500 400 300 200 100 0 1000 0 VOUT = 5V 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) PFM MODE VOUT = 3.3V VOUT = 3.3V VOUT = 5V L = 10H
MAX1705/6 TOC03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 100 L = 10H VOUT = 3.3V A: VIN = 0.9V B: VIN = 2.7V 1: PFM MODE 2: PWM MODE A.2 B.1 A.1 B.2
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 A.1 L = 10H VOUT = 5V A: VIN = 0.9V C: VIN = 2.4V E: VIN = 3.6V 1: PFM MODE 2: PWM MODE 0.1 1 10 100 B.1 A.2 C.1 B.2 C.2
1000
PWM MODE
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
MAX1706 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V)
MAX1705/6 TOC04
MAX1706 EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V)
MAX1705/6 TOC05
MAX1706 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
L = 22H MAXIMUM OUTPUT CURRENT (mA) 600 500 400 300 200 100 0 VOUT = 3.3V VOUT = 5V PFM MODE 0 0.5 1.0 1.5 2.0 2.5 3 3.5 4 4.5 PWM MODE VOUT = 5V VOUT = 3.3V
MAX1705/6 TOC06
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 100 L = 22H VOUT = 3.3V A: VIN = 0.9V B: VIN = 2.7V 1: PFM MODE 2: PWM MODE A.1 A.2 B.1 B.2
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.1 1 10 A.1 B.1 A.2 L = 22H VOUT = 5V A: VIN = 0.9V B: VIN = 2.4V C: VIN = 3.6V 1: PFM MODE 2: PWM MODE 100 C.1 B.2 C.2
700
1000
1000
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
MAX1705 START-UP INPUT VOLTAGE vs. OUTPUT CURRENT
MAX1705/6 TOC07
NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE
11 10 9 8 7 6 5 4 3 2 1 0 0 PWM MODE VOUT = 3.3V L = 10H
MAX1705/6 TOC8
LINEAR-REGULATOR DROPOUT VOLTAGE vs. LOAD CURRENT
VLDO = 3.3V
MAX1705/6 TOC09
2.3 2.1 START-UP INPUT VOLTAGE (V) 1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 0.01 0.1 1 10 100 NO-LOAD START-UP: 1.0V AT -40C 0.79 AT +25C 0.64V AT +85C CONSTANT-CURRENT LOAD VOUT = 3.3V L = 10H D1 = MBR0520L TA = -40C TA = +25C TA = +85C
12 NO-LOAD SUPPLY CURRENT (mA)
140 120 DROPOUT VOLTAGE (mV) 100 80 60 VLDO = 5V 40 20 VLDO = 2.5V
PFM MODE 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) 0 40 80 120 160 200 LOAD CURRENT (mA)
1000
OUTPUT CURRENT (mA)
6
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, TA = +25C, unless otherwise noted.)
LINEAR-REGULATOR POWER-SUPPLY REJECTION RATIO vs. FREQUENCY
MAX1705/6 TOC10
MAX1705/MAX1706
LINEAR-REGULATOR REGION OF STABLE C6 ESR vs. LOAD CURRENT
C6 = 22F UNCOMPENSATED C2 = 22pF (FEED FORWARD) 1
MAX1705/6 TOC11
60 50 40 30 20 10 0 100 1k 10k 100k 1M
100
10 C6 ESR ()
PSRR (dB)
VOUT = 4V TO 5V VLDO = 3.3V ILDO = 200mA C5 = 0.33F 10M
STABLE REGION 0.1
0 1 50 100 150 200 250 300
FREQUENCY (Hz)
MAX1705 NOISE SPECTRUM AT POUT (VOUT = 4.5V, VIN = 1.2V, 200mA LOAD)
LOAD CURRENT (mA)
NOISE (5mVRMS/div)
0V
1k
10k
100k FREQUENCY (Hz)
1M
10M
MAX1705 LINEAR-REGULATOR OUTPUT NOISE SPECTRUM (VLDO = 3.3V, VOUT = 4.5V, VIN = 1.2V, ILDO = 200mA)
MAX1705/6 TOC14
NOISE (50V/div)
0V
1k
10k
100k FREQUENCY (Hz)
1M
10M
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MAX1705/6 TOC13
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
____________________________Typical Operating Characteristics (continued)
(Circuit of Figure 2, TA = +25C, unless otherwise noted.)
MAX1705 LINE-TRANSIENT RESPONSE
MAX1705/6 TOC15
MAX1705 LOAD-TRANSIENT RESPONSE
MAX1705/6 TOC16
MAX1705 POWER-ON DELAY (PWM MODE)
MAX1705/6 TOC17
3V 2.5V
A
A B C
A
3.3V
B B D 200s/div IOUT = 0mA, VOUT = 3.3V A = VIN, 1.5V TO 2.0V, 200mV/div B = VOUT, 10mV/div, 3.3V DC OFFSET 200s/div VIN = 1.2V, VOUT = 3.3V A = VOUT, 50mV/div, 3.3V DC OFFSET B = IOUT, 0mA TO 200mA, 200mA/div 200s/div VIN = 1.2V, LOAD = 1k A = ONA, 2V/div B = VLDO, 2V/div C = VOUT, 2V/div D = INDUCTOR CURRENT, 500mA/div 0mA
MAX1705 PWM SWITCHING WAVEFORMS
MAX1705/6 TOC18
MAX1705 PFM SWITCHING WAVEFORMS
MAX1705/6 TOC19
MAX1705 LINEAR-REGULATOR OUTPUT NOISE
DC TO 500kHz 0mA
MAX1705/6 TOC20
A B
1A A 0V B
0V VOUT
C VOUT C
VLDO
D
VLDO
D
VLDO 2s/div VIN = 1.2V, VOUT = 4.5V, VLDO = 3.3V, ILDO = 40mA A = INDUCTOR CURRENT, 500mA/div B = LX VOLTAGE, 5V/div C = VOUT RIPPLE, 50mV/div AC COUPLED D = VLDO RIPPLE, 5mV/div AC COUPLED C5 = 0.33F 1ms/div VLDO IS AC COUPLED, 1mv/div ILDO = 200mA C5 = 0.33F
1s/div VIN = 1.2V, VOUT = 4.5V, VLDO = 3.3V, ILDO = 200mA A = INDUCTOR CURRENT, 500mA/div B = LX VOLTAGE, 5V/div C = VOUT RIPPLE, 50m/div AC COUPLED D = VLDO RIPPLE, 5m/div AC COUPLED C5 = 0.33F
8
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
______________________________________________________________Pin Description
PIN 1 2 3 4 5 6 NAME LBP LBN REF TRACK GND OUT FUNCTION Low-Battery Comparator Noninverting Input. Common-mode range is 0.5V to 1.5V. Low-Battery Comparator Inverting Input. Common-mode range is 0.5V to 1.5V. 1.250V Reference Output. Bypass REF with a 0.33F capacitor to GND. REF can source up to 50A. Track-Mode Control Input for DC-DC Converter. In track mode, the boost-converter output is sensed at OUT and set 0.3V above LDO to improve efficiency. Set TRACK to OUT for track mode. Connect TRACK to GND for normal operation. Ground Step-Up Converter Feedback Input, used during track mode. IC power and low-dropout linear-regulator input. Bypass OUT to GND with a 0.1F ceramic capacitor placed as close to the IC as possible. Step-Up DC-DC Converter Feedback Input. Connect FB to a resistor voltage divider between POUT and GND to set the output voltage between 2.5V and 5.5V. FB regulates to 1.233V. Low-Dropout Linear-Regulator Feedback Input. Connect FBLDO to a resistor voltage divider between LDO to GND to set the output voltage from 1.25V to VOUT - 0.3V (5.0V max). FBLDO regulates to 1.250V. Low-Dropout Linear-Regulator Output. LDO sources up to 200mA. Bypass to GND with a 22F capacitor. Low-Battery Comparator Output. This open-drain, N-channel output is low when LBP < LBN. Input hysteresis is 16mV. Switching-Mode Selection and External-Clock Synchronization Input: * CLK/SEL = low: low-power, low-quiescent-current PFM mode. * CLK/SEL = high: low-noise, high-power PWM mode. Switches at a constant frequency (300kHz). Full output power is available. * CLK/SEL = driven with an external clock: low-noise, high-power synchronized PWM mode. Synchronizes to an external clock (from 200kHz to 400kHz). Turning on the DC-DC converter with CLK/SEL = GND also serves as a soft-start function, since peak inductor current is reduced. Power Ground for the source of the N-channel power MOSFET switch Inductor connection to the drains of the P-channel synchronous rectifier and N-channel switch Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal operation (Table 2). On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal operation (Table 2). Boost DC-DC Converter Power Output. POUT is the source of the P-channel synchronous-rectifier MOSFET switch. Connect an external Schottky diode from LX to POUT. The output current available from POUT is reduced by the current drawn from the LDO linear-regulator output.
MAX1705/MAX1706
7
FB
8 9 10
FBLDO LDO LBO
11
CLK/SEL
12 13 14
PGND LX ONB ONA
15
16
POUT
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
_______________Detailed Description
The MAX1705/MAX1706 are designed to supply both power and low-noise circuitry in portable RF and dataacquisition instruments. They combine a linear regulator, step-up switching regulator, N-channel power MOSFET, P-channel synchronous rectifier, precision reference, and low-battery comparator in a single 16pin QSOP package (Figure 1). The switching DC-DC converter boosts a 1- or 2-cell input to an adjustable output between 2.5V and 5.5V. The internal low-dropout regulator provides linear post-regulation for noisesensitive circuitry, as well as outputs from 1.25V to 300mV below the switching-regulator output. The MAX1705/MAX1706 start from a low, 1.1V input and remain operational down to 0.7V. These devices are optimized for use in cellular phones and other applications requiring low noise during fullpower operation, as well as low quiescent current for maximum battery life during standby and shutdown. They feature constant-frequency (300kHz), low-noise pulse-width-modulation (PWM) operation with 300mA or 730mA output capability from one or two cells, respectively, with 3.3V output. A low-quiescent-current standby pulse-frequency-modulation (PFM) mode offers an output up to 60mA and 140A, respectively, and reduces quiescent power consumption to 500W. In shutdown mode, the quiescent current is further reduced to just 1A. Figure 2 shows the standard application circuit for the MAX1705 configured in highpower PWM mode. Additional features include synchronous rectification for high efficiency and improved battery life, and an uncommitted comparator for low-battery detection. A CLK/SEL input allows frequency synchronization to reduce interference. Dual shutdown controls allow shutdown using a momentary pushbutton switch and microprocessor control.
LBO LBP N LBN FBLDO OUT
THERMAL SENSOR
MAX1705 MAX1706
SHUTDOWN LOGIC MOSFET DRIVER WITH CURRENT LIMITING
OUT
ERROR AMP REF IC PWR 2.15V
P
LDO
POUT EN START-UP OSCILLATOR Q D Q PFM/PWM CONTROLLER P
GND
ONA ON ONB REF CLK/SEL VLDO FB TRACK VOUT - 300mV IFB RDY 1.250V REFERENCE EN 300kHz OSCILLATOR PFM/PWM MODE IREF PGND EN OSC N LX
Q
ICS
Figure 1. Functional Diagram
10 ______________________________________________________________________________________
1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
INPUT 0.9V TO 3.6V L1 10H (22H) C7 22F D1 R5 LBP (TO PGND) R6 C8 0.33F LBN REF LX POUT OUT TRACK PGND C9 0.33F C3 0.1F R1 191k C1* C4 220F (100F) (TO PGND) FB ONA ONB CLK/SEL LBO GND R3 165k C2* LDO FBLDO C5* 0.33F C6 22F R2 100k LDO OUTPUT 3.3V BOOST OUTPUT 3.6V
MAX1705 MAX1706
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATH.
R7 100k
R4 100k
*OPTIONAL. ( ) ARE FOR MAX1706.
Figure 2. Typical Operating Circuit (PWM Mode)
Step-Up Converter
The step-up switching DC-DC converter generates an adjustable output to supply both power circuitry (such as RF power amplifiers) and the internal low-dropout linear regulator. During the first part of each cycle, the internal N-channel MOSFET switch is turned on. This allows current to ramp up in the inductor and store energy in a magnetic field. During the second part of each cycle, when the MOSFET is turned off, the voltage across the inductor reverses and forces current through the diode and synchronous rectifier to the output filter capacitor and load. As the energy stored in the inductor is depleted, the current ramps down, and the output diode and synchronous rectifier turn off. Voltage across the load is regulated using either PWM or PFM operation, depending on the CLK/SEL pin setting (Table 1).
Table 1. Selecting the Operating Mode
CLK/SEL 0 1 External Clock (200kHz to 400kHz) MODE PFM PWM Synchronized PWM FEATURES Low supply current Low noise, high output current Low noise, high output current
devices can output up to 850mA. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. During PWM operation, each of the internal clock's rising edges sets a flip-flop, which turns on the N-channel MOSFET switch (Figure 3). The switch is turned off when the sum of the voltage-error and currentfeedback signals trips a multi-input comparator and resets the flip-flop; the switch remains off for the rest of the cycle. When a change occurs in the output voltage error signal into the comparator, it shifts the level that the inductor current is allowed to ramp to during each cycle and modulates the MOSFET switch pulse width. A second comparator enforces a 1.55A (max) inductor11
Low-Noise, High-Power PWM Operation When CLK/SEL is pulled high, the MAX1705/MAX1706 operate in a high-power, low-noise PWM mode. During PWM operation, they switch at a constant frequency (300kHz), and modulate the MOSFET switch pulse width to control the power transferred per cycle and regulate the voltage across the load. In PWM mode, the
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
POUT Q IFB* IREF* R Q N LX IFB* ICS IREF* CURRENT LIMIT LEVEL OSC PGND CURRENT LIMIT LEVEL PGND *SEE FIGURE 1 R S Q N LX D LOGIC HIGH POUT R P Q
P
S
Figure 3. Simplified PWM Controller Block Diagram
*SEE FIGURE 1
current limit for the MAX1705, and 950mA (max) for the MAX1706. During PWM operation, the circuit operates with a continuous inductor current.
Figure 4. Controller Block Diagram in PFM Mode
Synchronized PWM Operation The MAX1705/MAX1706 can also be synchronized to a 200kHz to 400kHz frequency by applying an external clock to CLK/SEL. This allows the user to set the harmonics, to avoid IF bands in wireless applications. The synchronous rectifier is also active during synchronized PWM operation. Low-Power PFM Operation Pulling CLK/SEL low places the MAX1705/MAX1706 in low-power standby mode. During standby mode, PFM operation regulates the output voltage by transferring a fixed amount of energy during each cycle, and then modulating the switching frequency to control the power delivered to the output. The devices switch only as needed to service the load, resulting in the highest possible efficiency at light loads. Output current capability in PFM mode is 140mA (from 2.4V input to 3.3V output). The output is regulated at 1.3% above the PWM threshold. During PFM operation, the error comparator detects output voltage falling out of regulation and sets a flip-flop, turning on the N-channel MOSFET switch (Figure 4). When the inductor current ramps to the PFM mode current limit (435mA) and stores a fixed amount of energy, the current-sense comparator resets a flipflop. The flip-flop turns off the N-channel switch and turns on the P-channel synchronous rectifier. A second flip-flop, previously reset by the switch's "on" signal, inhibits the error comparator from initiating another
12
cycle until the energy stored in the inductor is dumped into the output filter capacitor and the synchronous rectifier current ramps down to 70mA. This forces operation with a discontinuous inductor current.
Synchronous Rectifier The MAX1705/MAX1706 feature an internal 270m, P-channel synchronous rectifier to enhance efficiency. Synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous step-up regulators. In PWM mode, the synchronous rectifier is turned on during the second half of each cycle. In PFM mode, an internal comparator turns on the synchronous rectifier when the voltage at LX exceeds the step-up converter output, and then turns it off when the inductor current drops below 70mA.
Linear Regulator
The internal low-dropout linear regulator steps down the output from the step-up converter and reduces switching ripple. It is intended to power noise-sensitive analog circuitry, such as low-noise amplifiers and IF stages in cellular phones and other instruments, and can deliver up to 200mA. However, in practice, the maximum output current is further limited by the current available from the boost converter and by the voltage differential between OUT and LDO. Use a 22F capacitor with a 1 or less equivalent series resistance (ESR) at the output for stability (see the Linear Regulator Region of Stable C6 ESR vs. Load Current graph in the Typical Operating Characteristics). During power-up, the linear regulator remains off until the step-up converter goes into regulation for the first time.
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
The linear regulator in the MAX1705/MAX1706 features a 0.5, P-channel MOSFET pass transistor. This provides several advantages, including longer battery life, over similar designs using a PNP pass transistor. The P-channel MOSFET requires no base-drive current, which reduces quiescent current considerably. PNPbased regulators tend to waste base-drive current in dropout when the pass transistor saturates. The MAX1705/MAX1706 eliminate this problem. The linear-regulator error amplifier compares the output feedback sensed at the FBLDO input against the internal 1.250V reference, and amplifies the difference (Figure 1). The MOSFET driver reads the error signal and applies the appropriate drive to the P-channel pass transistor. If the feedback signal is lower than the reference, the pass-transistor gate is pulled lower, allowing more current to pass to the output, thereby increasing the output voltage. If the feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to pass to the output. Additional blocks include a current-limiting block and a thermal-overload protection block.
MAX1705/MAX1706
Table 2. On/Off Logic Control
ONA 0 0 1 1 ONB 0 1 0 1 MAX1705/MAX1706 On Off On On
Tracking
Connecting TRACK to the step-up converter output implements a tracking mode that sets the step-up converter output to 300mV above the linear-regulator output, improving efficiency. In track mode, feedback for the step-up converter is derived from the OUT pin. When TRACK is low, the step-up converter and linear regulator are separately controlled by their respective feedback inputs, FB and FBLDO. TRACK is a logic input with a 0.5VOUT threshold, and should be hardwired or switched with a slew rate exceeding 1V/s. VLDO must be set above 2.3V for track mode to operate properly. On power-up with TRACK = OUT, the step-up converter initially uses the FB input to regulate its output. After the step-up converter goes into regulation for the first time, the linear regulator turns on. When the linear regulator reaches 2.3V, track mode is enabled and the stepup converter is regulated to 300mV above the linearregulator output.
Low-Voltage Start-Up Oscillator
The MAX1705/MAX1706 use a CMOS, low-voltage start-up oscillator for a 1.1V guaranteed minimum startup input voltage at +25C. On start-up, the low-voltage oscillator switches the N-channel MOSFET until the output voltage reaches 2.15V. Above this level, the normal step-up converter feedback and control circuitry take over. Once the device is in regulation, it can operate down to a 0.7V input, since internal power for the IC is bootstrapped from the output using the OUT pin. To reduce current loading during step-up, the linear regulator is kept off until the start-up converter goes into regulation. Minimum start-up voltage is influenced by load and temperature (see the Typical Operating Characteristics). To allow proper start-up, do not apply a full load at POUT until after the device has exited start-up mode and entered normal operation.
Low-Battery Comparator
The internal low-battery comparator has uncommitted inputs and an open-drain output capable of sinking 1mA. To use it as a low-battery-detection comparator, connect the LBN input to the reference, and connect the LBP input to an external resistor divider between the positive battery terminal and GND (Figure 2). The resistor values are then as follows: VIN,TH - 1 R5 = R6 VLBN where VIN,TH is the desired input voltage trip point and VLBN = VREF = 1.25V. Since the input bias current into LBP is less than 50nA, R6 can be a large value (such as 270k or less) without sacrificing accuracy. Connect the resistor voltage divider as close to the IC as possible, within 0.2in. (5mm) of the LBP pin. The inputs have a 0.5V to 1.5V common-mode input range, and a 16mV input-referred hysteresis.
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Shutdown
The MAX1705/MAX1706 feature a shutdown mode that reduces quiescent current to less than 1A, preserving battery life when the system is not in use. During shutdown, the reference, the low-battery comparator, and all feedback and control circuitry are off. The step-up converter's output drops to one Schottky diode drop below the input, but the linear regulator output is turned off. Entry into shutdown mode is controlled by logic input pins ONA and ONB (Table 2). Both inputs have trip points near 0.5VOUT with 0.15VOUT hysteresis.
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
The low-battery comparator can also be used to monitor the output voltage, as shown in Figure 5. To set the low-battery threshold to a voltage below the 1.25V reference, insert a resistor divider between REF and LBN, and connect the battery to the LBP input through a 10k current-limiting resistor (Figure 6). The equation for setting the resistors for the low-battery threshold is then as follows: V R5 = R6 REF - 1 VIN,TH Alternatively, the low-battery comparator can be used to check the output voltage or to control the load directly on POUT during start-up (Figure 7). Use the following equation to set the resistor values: VOUT,TH - 1 R5 = R6 VLBP where VOUT,TH is the desired output voltage trip point and VLBP is connected to the reference or 1.25V.
0.33F POUT LDO
MAX1705 MAX1706
LBO LBN REF GND LBP
R5
R6
Figure 5. Using the Low-Battery Comparator to Sense the Output Voltage
POUT REF
MAX1705 MAX1706
LBO R8 10k LBP BATTERY VOLTAGE GND LBN
R5
0.33F
Reference
The MAX1705/MAX1706 have an internal 1.250V, 1% bandgap reference. Connect a 0.33F bypass capacitor to GND within 0.2in. (5mm) of the REF pin. REF can source up to 50A of external load current.
R6
_________________ Design Procedure
Setting the Output Voltages
Set the step-up converter output voltage between 2.5V and 5.5V by connecting a resistor voltage-divider to FB from OUT to GND, as shown in Figure 8. The resistor values are then as follows: V R1 = R2 POUT - 1 VFB where VFB, the step-up regulator feedback setpoint, is 1.233V. Since the input bias current into FB is less than 50nA, R2 can have a large value (such as 270k or less) without sacrificing accuracy. Connect the resistor voltage-divider as close to the IC as possible, within 0.2in. (5mm) of the FB pin. Alternatively, set the step-up converter output to track the linear regulator by 300mV. To accomplish this, set TRACK to OUT.
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C5 270k
Figure 6. Detecting Battery Voltages Below 1.25V
P
STEP-UP OUTPUT C3 0.1F C4
OUT
POUT LBN
R5
MAX1705
LBO MAX1706 LBP REF GND 0.33F
R6
Figure 7. Using the Low-Battery Comparator for Load Control During Start-Up
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
To set the low-dropout linear-regulator output, use a resistor voltage-divider connected to FBLDO from LDO to GND. Set the output to a value at least 300mV less than the step-up converter output using the following formula: V R3 = R4 LDO - 1 VFBLDO where VFBLDO, the linear-regulator feedback trip point, is 1.250V. Since the input bias current into FBLDO is less than 50nA, R4 can be a large value (such as 270k or less). Connect the resistor voltage-divider as close to the IC as possible, within 0.2in. (5mm) of the FBLDO pin. MUR150 or EC11FS1). Do not use ordinary rectifier diodes, since slow switching speeds and long reverse recovery times compromise efficiency and load regulation.
MAX1705/MAX1706
Choose Input and Output Filter Capacitors
Choose input and output filter capacitors that service the input and output peak currents with acceptable voltage ripple. Choose input capacitors with working voltage ratings over the maximum input voltage, and output capacitors with working voltage ratings higher than the output. A 100F, 100m, low-ESR tantalum capacitor is recommended at the MAX1706's step-up output. For the MAX1705, use two in parallel or a 220F low-ESR tantalum capacitor. The input filter capacitor (C7) also reduces peak currents drawn from the input source and reduces input switching noise. The input voltage source impedance determines the size required for the input capacitor. When operating directly from one or two NiCd cells placed close to the MAX1705/MAX1706, use a 22F, low-ESR input filter capacitor. When operating from a power source placed farther away, or
Inductor Selection
The MAX1705/MAX1706's high switching frequency allows the use of a small surface-mount inductor. Use a 10H inductor for the MAX1705 and a 22H inductor for the MAX1706. Make sure the saturation-current rating exceeds the N-channel switch current limit of 1.55A for the MAX1705 and 950mA for the MAX1706. For high efficiency, chose an inductor with a high-frequency core material, such as ferrite, to reduce core losses. To minimize radiated noise, use a torroid, pot core, or shielded-bobbin inductor. See Table 3 for suggested parts and Table 4 for a list of inductor suppliers. Connect the inductor from the battery to the LX pin as close to the IC as possible.
LINEARREGULATOR OUTPUT
LDO
POUT
STEP-UP OUTPUT
Attaching the Output Diode
Use a Schottky diode, such as a 1N5817, MBR0520L, or equivalent. The Schottky diode carries current during start-up, and in PFM mode after the synchronous rectifier turns off. Thus, the current rating only needs to be 500mA. Attach the diode between the LX and POUT pins, as close to the IC as possible. In high-temperature applications, some Schottky diodes may be unsuitable due to high reverse-leakage currents. Try substituting a Schottky diode with a higher reverse voltage rating, or use an ultra-fast silicon rectifier with reverse recover times less than 60ns (such as a
C2*
R3
MAX1705 MAX1706
OUT
R1
C1*
FBLDO R4 GND
FB PGND R2
* OPTIONAL COMPENSATION CAPACITORS
Figure 8. Feedback Connections for the MAX1705/MAX1706
Table 3. Component Selection Guide
PRODUCTION Surface Mount INDUCTORS Sumida CDR63B, CD73, CDR73B, CD74B series Coilcraft DO1608, DO3308, DT3316 series Sumida RCH654 series CAPACITORS Matsuo 267 series Sprague 595D series AVX TPS series Sanyo OS-CON series Nichicon PL series DIODES Motorola MBR0520L
Through Hole
Motorola 1N5817 15
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
from higher-impedance batteries, consider using one or two 100F, 100m, low-ESR tantalum capacitors. Low-ESR capacitors are recommended. Capacitor ESR is a major contributor to output ripple--often more than 70%. Ceramic, Sanyo OS-CON, and Panasonic SP/CB-series capacitors offer the lowest ESR. Low-ESR tantalum capacitors are second best and generally offer a good trade-off between price and performance. Do not exceed the ripple-current ratings of tantalum capacitors. Avoid aluminum-electrolytic capacitors, since their ESR is too high.
Table 4. Component Suppliers
SUPPLIER AVX Coilcraft Matsuo Motorola Sanyo Sumida PHONE USA: (803) 946-0690 (800) 282-4975 USA: (847) 639-6400 USA: (714) 969-2491 USA: (602) 303-5454 USA: (619) 661-6835 Japan: 81-7-2070-6306 USA: (847) 956-0666 Japan: 81-3-3607-5111 FAX (803) 626-3123 (847) 639-1469 (714) 960-6492 (602) 994-6430 (619) 661-1055 81-7-2070-1174 (847) 956-0702 81-3-3607-5144
Adding Bypass Capacitors
Several ceramic bypass capacitors are required for proper operation of the MAX1705/MAX1706. Bypass REF with a 0.33F capacitor to GND. Connect a 0.1F ceramic capacitor from OUT to GND and a 0.33F ceramic capacitor from POUT to PGND. Place a 22F, low-ESR capacitor and an optional 0.33F ceramic capacitor from the linear-regulator output LDO to GND. An optional 22pF ceramic capacitor can be added to the linear-regulator feedback network to reduce noise (C2, Figure 2). Place each of these as close to their respective pins as possible, within 0.2in. (5mm) of the DC-DC converter IC. High-value, low-voltage, surfacemount ceramic capacitors are now readily available in small packages; see Table 4 for suggested suppliers.
ground plane. Instead, place them close together and route them in a star-ground configuration using component-side copper. Then connect the star ground to the internal ground plane using vias. Keep the voltage-feedback networks very close to the MAX1705/MAX1706--within 0.2in. (5mm) of the FB and FBLDO pins. Keep noisy traces, such as from the LX pin, away from the reference and voltage-feedback networks, especially the LDO feedback, and separated from them using grounded copper. Consult the MAX1705/MAX1706 EV kit for a full PC board example.
__________ Applications Information
Use in a Typical Wireless Phone Application
The MAX1705/MAX1706 are ideal for use in digital cordless and PCS phones. The power amplifier (PA) is connected directly to the step-up converter output for maximum voltage swing (Figure 9). The internal linear regulator is used for post-regulation to generate lownoise power for DSP, control, and RF circuitry. Typically, RF phones spend most of their life in standby mode and short periods in transmit/receive mode. During standby, maximize battery life by setting CLK/SEL = GND and TRACK = OUT; this places the IC in PFM and track modes (for lowest quiescent power consumption). In transmit/receive mode, set TRACK = GND and CLK/SEL = OUT to increase the PA supply voltage and initiate high-power, low-noise PWM operation. Table 5 lists the typical available output current when operating with one or more NiCd/NiMH cells or one Li-Ion cell.
Designing a PC Board
High switching frequencies and large peak currents make PC board layout an important part of design. Poor design can cause excessive EMI and groundbounce, both of which can cause instability or regulation errors by corrupting voltage- and currentfeedback signals. It is highly recommended that the PC board example of the MAX1705 evaluation kit (EV kit) be followed. Power components--such as the inductor, converter IC, filter capacitors, and output diode--should be placed as close together as possible, and their traces should be kept short, direct, and wide. Place the LDO output capacitor as close to the LDO pin as possible. Make the connection between POUT and OUT very short. Keep the extra copper on the board, and integrate it into ground as a pseudo-ground plane. On multilayer boards, do not connect the ground pins of the power components using vias through an internal
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
270k LX CONTROL INPUTS GND POUT C
MAX1705 MAX1706
ONB OUT VDD I/O ONA I/O
MAX1705 MAX1706
LDO
ON/OFF
I/O C
PA RF 0.1F 270k
Figure 9. Typical Phone Application
Figure 10. Momentary Pushbutton On/Off Switch
Table 5. Typical Available Output Current
NUMBER OF CELLS 1 NiCd/NiMH 2 NiCd/NiMH 2 NiCd/NiMH 3 NiCd/NiMH or 1 Li-Ion INPUT VOLTAGE (V) 1.2 2.4 2.4 3.6 STEP-UP OUTPUT VOLTAGE: (PA POWER SUPPLY) (V) 3.3 3.3 5.0 5.0 TOTAL OUTPUT CURRENT (mA) MAX1705 300 730 500 850 MAX1706 200 450 350 550
Implementing Soft-Start
To implement soft-start, set CLK/SEL low on power-up; this forces PFM operation and reduces the peak switching current to 435mA. Once the circuit is in regulation, CLK/SEL can be set high for full-power operation.
___________________Chip Information
TRANSISTOR COUNT: 1649 SUBSTRATE CONNECTED TO GND
Adding a Manual Power Reset
A momentary pushbutton switch can be used to turn the MAX1705/MAX1706 on and off (Figure 10). ONA is pulled low and ONB is pulled high to turn the part off. When the momentary switch is pressed, ONB is pulled low and the regulator turns on. The switch must be pressed long enough for the microcontroller (C) to exit reset (200ms) and drive ONA high. A small capacitor is added to help debounce the switch. The C issues a logic high to ONA, which holds the part on regardless of the switch state. To turn the regulator off, press the switch again, allowing the C to read the switch status and pull ONA low. When the switch is released, ONB is pulled high.
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
__________________________________________________Tape-and-Reel Information
4.0 0.1 1.0 0.1 1.5 +0.1/-0.0 DIAMETER 2.0 0.05 1.75 0.1 A
3.5 0.05 2.2 0.1
8.0 0.3
0.5 RADIUS TYPICAL Bo 0.30 0.05 0.8 0.05 0.30R MAX.
4.0 0.1
A0 A
1.0 MINIMUM
Ko
Ao = 3.1mm 0.1 Bo = 2.7mm 0.1 Ko = 1.2mm 0.1
NOTE: DIMENSIONS ARE IN MM. AND FOLLOW EIA481-1 STANDARD.
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator
________________________________________________________Package Information
QSOP.EPS
MAX1705/MAX1706
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1- to 3-Cell, High-Current, Low-Noise, Step-Up DC-DC Converters with Linear Regulator MAX1705/MAX1706
NOTES
20
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