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19-4759; Rev 1; 1/99
ANUAL N KIT M LUATIO ATA SHEET EVA WS D FOLLO
1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
General Description Features
o Up to 96% Efficiency o 1.1 VIN Guaranteed Start-Up o 0.7V to 5.5V Input Range o Up to 800mA Output o Step-Up Output (adjustable from 2.5V to 5.5V) o PWM/PFM Synchronous-Rectified Topology o External Clock or Internal 300kHz Oscillator o 3A Logic-Controlled Shutdown o Power-Good Output (MAX1701) o Low-Battery Comparator (MAX1701) o Uncommitted Gain Block (MAX1701)
MAX1700/MAX1701
The MAX1700/MAX1701 are high-efficiency, low-noise, step-up DC-DC converters intended for use in batterypowered wireless applications. They use a synchronous-rectified pulse-width-modulation (PWM) boost topology to generate 2.5V to 5.5V outputs from battery inputs such as one to three NiCd/NiMH cells or one LiIon cell. Both devices have an internal 1A, 130m Nchannel MOSFET switch and a 250m P-channel synchronous rectifier. With their internal synchronous rectifier, the MAX1700/ MAX1701 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 3A shutdown mode. The MAX1700/MAX1701 come in 16-pin QSOP packages (which occupy the same space as an 8-pin SO). The MAX1701 includes two comparators to generate power-good and low-battery warning outputs. It also contains a gain block that can be used to build a linear regulator using an external P-channel pass device. For higher-power outputs, refer to the MAX1703. For dual outputs (step-up and linear regulator), refer to the MAX1705/MAX1706. For an on-board analog-to-digital converter, refer to the MAX848/MAX849. The MAX1701 evaluation kit is available to speed design time.
Ordering Information
PART MAX1700EEE MAX1701EEE TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 QSOP
Applications
Digital Cordless Phones PCS Phones Wireless Handsets Two-Way Pagers
TOP VIEW
I.C. 1 I.C. 2 REF 3 CLK/SEL 4 GND 5 I.C. 6 ONB 7 ONA 8 16 I.C. 15 POUT 14 OUT
Typical Operating Circuit
INPUT 0.7V TO 5.5V
Personal Communicators Palmtop Computers Hand-Held Instruments
Pin Configurations
ON OFF OFF ON PWM PFM OR ONB CLK/SEL POUT
MAX1700
ONA LX
OUTPUT 3.3V OR ADJ UP TO 800mA
SYNC
MAX1700
13 LX 12 PGND 11 FB 10 I.C. 9 I.C.
REF FB
OUT GND PGND
QSOP
I.C. = INTERNAL CONNECTION. LEAVE OPEN OR CONNECT TO GND
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, OUT, AO, POK, LBO to GND...................-0.3V, +6V PGND to GND.....................................................................0.3V LX to PGND.....................................................-0.3V,VPOUT+0.3V CLK/SEL, AIN, REF, FB, LBP, LBN, POUT to GND............-0.3V, VOUT+0.3V ................................................................................... Continuous Power Dissipation (TA=+70C) 16-QSOP (Derate 8.30mW/C above +70C) ...............667mW Operating Temperature Ranges MAX1700EEE, MAX1701EEE ...........................-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
(CLK/SEL = ONA = ONB = FB = PGND = GND, OUT = POUT, VOUT = 3.6V (Note 6); MAX1701: AIN = LBN = GND, LBP = REF, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER DC-DC CONVERTER Input Voltage Range (Note 1) Minimum Start-Up Voltage (Note 2) Frequency in Start-Up Mode Output Voltage (Note 3) FB Regulation Voltage FB Input Current Output Voltage Adjust Range Output Voltage Lockout Threshold Load Regulation (Note 5) Supply Current in Shutdown Supply Current in Low-Power Mode (Note 6) Supply Current in Low-Noise Mode (Note 6) DC-DC SWITCHES POUT Leakage Current LX Leakage Current Switch On-Resistance VLX = 0V, VOUT = 5.5V VLX = V ONB = VOUT = 5.5V N-channel P-channel N-Channel Current Limit P-Channel Turn-Off Current CLK/SEL = OUT CLK/SEL = GND CLK/SEL = GND 1100 250 20 CLK/SEL = GND CLK/SEL = OUT 0.1 0.1 0.2 0.13 0.25 1300 400 20 20 0.45 0.28 0.5 1600 550 120 mA mA A A (Note 4) CLK/SEL = OUT, No load to full load V ONB = 3.6V CLK/SEL = GND (MAX1700) CLK/SEL = GND (MAX1701) CLK/SEL = OUT (MAX1700) CLK/SEL = OUT (MAX1701) MAX1700 MAX1701 ILOAD < 1mA, TA = +25C VOUT = 1.5V VFB < 0.1V, CLK/SEL = OUT, VBATT = 2.4V, includes load regulation error for 0A ILX 0.55A Adjustable output, CLK/SEL = OUT, VBATT = 2.4V, includes load regulation error for 0A ILX 0.55A VFB = 1.25V 2.5 2.0 2.15 -1.6 0.1 3 35 55 125 140 20 20 70 110 250 300 40 3.17 1.210 0.7 0.9 150 3.30 1.24 0.01 5.5 1.1 300 3.38 1.255 20 5.5 2.3 V V kHz V V nA V V % A A A CONDITIONS MIN TYP MAX UNITS
2
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONA = ONB = FB = PGND = GND, OUT = POUT, VOUT = 3.6V (Note 6); MAX1701: AIN = LBN = GND, LBP = REF, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER GAIN BLOCK (MAX1701) AIN Reference Voltage AIN Input Current Transconductance AO Output Low Voltage AO Output High Leakage POWER GOOD (MAX1701) Internal Trip Level External Trip Level POK Low Voltage POK High Leakage Current LOW-BATTERY COMPARATOR LBN, LBP Input Offset LBN, LBP Common Mode Range LBO Output Low Voltage LBO High Leakage LBN, LBP Input Current REFERENCE Reference Output Voltage REF Load Regulation REF Supply Rejection LOGIC AND CONTROL INPUTS Input Low Voltage (Note 7) Input High Voltage (Note 7) Input High Voltage (Note 7) Logic Input Current Internal Oscillator Frequency Oscillator Maximum Duty Cycle External Clock Frequency Range Minimum CLK/SEL Pulse Width Maximum CLK/SEL Rise/Fall Time 1.2V < VOUT < 5.5V, ONA and ONB 2.5V < VOUT < 5.5V, CLK/SEL 1.2V < VOUT < 5.5V, ONA and ONB 2.5V < VOUT < 5.5V, CLK/SEL ONA, ONB, and CLK/SEL CLK/SEL = OUT 0.8VOUT 0.8VOUT -1 260 80 200 200 100 300 86 1 340 90 400 0.2VOUT 0.2VOUT V V A kHz % kHz ns ns IREF = 0 -1A < IREF < 50A 2.5V < VOUT < 5V 1.237 1.250 5 0.2 1.263 15 5 V mV mV LBP falling, 15mV hysteresis To maintain input offset < 5mV (at least one input must be within this range) ISINK = 1mA, VOUT = 3.6V or ISINK = 20A, VOUT = 1V VOUT = VLBO = 5V VLBP = VLBN = 1.5V -5 0.5 0.03 0.01 0.5 5 1.5 0.4 1 20 mV V V A nA Rising VOUT, VFB < 0.1V Rising VFB ISINK = 1mA, VOUT = 3.6V or ISINK = 20A, VOUT = 1V VOUT = VPOK = 5.5V 2.93 1.1 2.97 1.12 0.03 0.01 3.02 1.14 0.4 1 V V V A IAO = 20A VAIN = 1.5V 10A < IAO = 100A VAIN = 0.7V, IAO = 100A VAIN = 1.5V, VAO = 5.5V 1.237 -30 5 9 0.1 0.01 1.25 1.263 30 16 0.4 1 V nA mmho V A CONDITIONS MIN TYP MAX UNITS
MAX1700/MAX1701
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3
1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONA = ONB = FB = PGND = GND, OUT = POUT, VOUT = 3.6V (Note 6); MAX1701: AIN = LBN = GND, LBP = REF, TA = -40C to +85C, unless otherwise noted.) (Note 8) PARAMETER DC-DC CONVERTER Output Voltage (Note 3) FB Regulation Voltage Output Voltage Lockout Threshold Supply Current in Shutdown Supply Current in Low-Power Mode (Note 6) Supply Current in Low-Noise Mode (Note 6) DC-DC SWITCHES Switch On-Resistance N-channel P-channel N-Channel Current Limit GAIN BLOCK (MAX1701) AIN Reference Voltage Transconductance POWER-GOOD (MAX1701) Internal Trip Level External Trip Level LBN, LBP Input Offset LBN, LBP Common Mode Range REFERENCE Reference Output Voltage IREF = 0 1.23 1.27 V Rising VOUT, VFB < 0.1V Rising VFB LBP falling, 15mV hysteresis To maintain input offset < 5mV (at least one input must be within this range) 2.92 1.1 -5 0.5 3.03 1.14 5 1.5 V V mV V IAO = 20A 10A < IAO < 100A 1.23 5 1.27 16 V mmho CLK/SEL = OUT CLK/SEL = GND 1100 250 CLK/SEL = GND CLK/SEL = OUT 0.45 0.28 0.5 1800 600 mA VFB < 0.1V, CLK/SEL = OUT, VBATT = 2.4V, includes load regulation error for 0A ILX 0.55A Adjustable output, CLK/SEL = OUT, VBATT = 2.4V, includes load regulation error for 0A ILX 0.55A (Note 4) V ONB = 3.6V CLK/SEL = GND (MAX1700) CLK/SEL = GND (MAX1701) CLK/SEL = OUT (MAX1700) CLK/SEL = OUT (MAX1701) 3.17 1.20 2.0 3.38 1.27 2.3 20 70 110 250 300 V V V A A A CONDITIONS MIN TYP MAX UNITS
LOW-BATTERY COMPARATOR (MAX1701)
4
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONA = ONB = FB = PGND = GND, OUT = POUT, V OUT = 3.6V, MAX1701: AIN = LBN = GND, LBP = REF, TA = -40C to +85C, unless otherwise noted.) (Note 8) PARAMETER LOGIC AND CONTROL INPUTS Input Low Voltage (Note 7) Input High Voltage (Note 7) Input High Voltage (Note 7) Logic Input Current Internal Oscillator Frequency Oscillator Maximum Duty Cycle External Clock Frequency Range 1.2V < VOUT < 5.5V, ONA and ONB 2.5V < VOUT < 5.5V, CLK/SEL 1.2V < VOUT < 5.5V, ONA and ONB 2.5V < VOUT < 5.5V, CLK/SEL ONA, ONB, and CLK/SEL CLK/SEL = OUT 0.8VOUT 0.8VOUT -1 260 80 200 1 340 92 400 0.2VOUT 0.2VOUT V V A kHz % kHz CONDITIONS MIN TYP MAX UNITS
MAX1700/MAX1701
Note 1: Operating voltage. Since the regulator is bootstrapped to the output, once started it will operate down to 0.7V input. Note 2: Start-up is tested with the circuit of Figure 2. Note 3: In low-power mode (CLK/SEL = GND), the output voltage regulates 1% higher than low-noise mode (CLK/SEL = OUT or synchronized). Note 4: The regulator is in start-up mode until this voltage is reached. Do not apply full load current. Note 5: Load regulation is measured from no-load to full load where full load is determined by the N-channel switch current limit. Note 6: Supply current from the 3.30V output is measured between the 3.30V output and the OUT pin. This current correlates directly to the actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. Set VOUT = 3.6V to keep the internal switch open when measuring the current into the device. Note 7: ONA and ONB have hysteresis of approximately 0.15xVOUT. Note 8: Specifications to -40C are guaranteed by design and not production tested.
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX1701 SHUTDOWN CURRENT vs. INPUT VOLTAGE (V)
MAX1700-02 MAX1770-03
EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V)
MAX1700-01
EFFICIENCY vs. LOAD CURRENT (VOUT = 5V)
100 VIN = 3.6V 90 80 70 60 50 VIN = 1.2V VIN = 2.4V 7.0 6.0 SHUTDOWN CURRENT (A) 5.0 4.0 3.0 2.0 1.0 0 0.1 1 10 100 1000 0 1
100 90 EFFICIENCY (%) 80 70 60 50 40 0.1 1 10 100 VIN = 1.2V VIN = 2.4V
T = 25C
EFFICIENCY (%)
T = 85C
VIN = 0.9V PFM PWM 1000
T = -40C
40 30
PFM PWM
2
3
4
5
6
LOAD CURRENT (mA)
LOAD CURRENT (mA)
INPUT VOLTAGE (V)
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5
1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
REFERENCE VOLTAGE vs. TEMPERATURE
MAX1700-04
REFERENCE VOLTAGE vs. REFERENCE CURRENT
MAX1700-05
FREQUENCY vs. TEMPERATURE
320 315 FREQUENCY (kHz) 310 305 300 295 290 285 VOUT = 3.3V VOUT = 5V
MAX1700-06
1.254
1.254
325
REFERENCE VOLTAGE (V)
1.250
REFERENCE VOLTAGE (V)
1.252
1.252
1.250
1.248
1.248
1.246
1.246
1.244 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
1.244 0 10 20 30 40 50 60 70 80 REFERENCE CURRENT (A)
280 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
START-UP INPUT VOLTAGE vs. OUTPUT CURRENT
MAX1700/01 TOC06a
PEAK INDUCTOR CURRENT vs. OUTPUT VOLTAGE
MAX1700-08
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
1.6 1.4 CURRENT LIMIT (A) 1.2 1.0 0.8 0.6 0.4 PFM 0.2 PWM
1000
2.5
3
3.5
4
4.5
5
5.5
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
HEAVY-LOAD SWITCHING WAVEFORMS (VOUT = 3.3V)
MAX1700-08
LINE-TRANSIENT RESPONSE
MAX1700-09
VOUT A 0V B 0V 0A C B A
1s/div VIN = 1.1V, IOUT = 200mA, VOUT = 3.3V A = LX VOLTAGE, 2V/div B = INDUCTOR CURRENT, 0.5A/div C = VOUT RIPPLE, 50mV/div, AC COUPLED IOUT = 0mA, VOUT = 3.3V
5ms/div A = VIN, 1.1V TO 2.1V, 1V/div B = VOUT RIPPLE, 50mV/div, AC COUPLED
6
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
Typical Operating Characteristics (continued)
(Circuit of Figure 1, TA = +25C, unless otherwise noted.)
LOAD-TRANSIENT RESPONSE
MAX1700-10
MAX1700/MAX1701
POWER-ON DELAY (PFM MODE)
MAX1700-11
3.3V A 200mA 0A A B
B
C
0mA
2ms/div VIN = 1.1V, VOUT = 3.3V A = LOAD CURRENT, 0mA TO 200mA, 0.2A/div B = VOUT RIPPLE, 50mV/div, AC COUPLED
5ms/div A = VON1, 2V/div B = VOUT, 1V/div C = INPUT CURRENT, 0.2A/div
GSM LOAD-TRANSIENT RESPONSE
MAX1700-12
DECT LOAD-TRANSIENT RESPONSE
MAX1700-13
5V A A
3.3V
B 0A
B 0A
1ms/div VIN = 3.6V, VOUT = 5V, COUT = 440F A = VOUT RIPPLE, 200mV/div, AC COUPLED B = LOAD CURRENT, 100mA TO 1A, 0.5A/div, PULSE WIDTH = 577s
2ms/div VIN = 1.2V, VOUT = 3.3V, COUT = 440F A = VOUT RIPPLE, 200mV/div, AC COUPLED B = LOAD CURRENT, 50mA TO 400mA, 0.2A/div, PULSE WIDTH = 416s
NOISE SPECTRUM (VOUT = 3.3V, VIN = 1.2V, RLOAD = 50)
MAX1700-14
2.7
NOISE (mVRMS) 0 0.1k 1k 10k FREQUENCY (Hz) 100k 1M
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7
1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
Pin Description
PIN MAX1700 -- -- 3 MAX1701 1 2 3 LBP LBN REF Low-Battery Comparator Non-Inverting Input Low-Battery Comparator Inverting Input Reference Output. Bypass with a 0.22F capacitor to GND. REF can source up to 50A. Switching-Mode Selection and External-Clock Synchronization Inputs. * CLK/SEL=Low: Low-power, delivers up to 10% of full load current. * CLK/SEL=High: High-power PWM mode. Full output power available. Operates in low-noise, constant-frequency mode. * CLK/SEL=External Clock: High-power PWM mode with the internal oscillator synchronized to the external clock. Turning on with CLK/SEL=0V also serves as a soft-start function since peak inductor current is limited to 25% of that allowed in PWM mode. Ground Power-Okay Comparator Output. Open drain N-channel output is low when VOUT is 10% below regulation point. No internal delay is provided. Shutdown Input. When ONB =high and ONA=low, the IC is off and the load is connected to the battery through the Schottky diode. Turn ON Input. When ONA=high or ONB =low, the IC turns on. Gain Block Output. This open-drain output sinks when VAIN LBP Input hysteresis is 15mV. Internal Connection. Leave open or connect to GND. NAME FUNCTION
4
4
CLK/SEL
5 -- 7 8 -- --
5 6 7 8 9 10
GND POK ONB ONA AO AIN
11 12 13 14 15 -- 1, 2, 6, 9, 10, 16
11 12 13 14 15 16 --
FB PGND LX OUT POUT LBO I.C.
8
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
OUT IC PWR 2.25V START-UP EN OSCILLATOR Q D PFM/PWM CONTROLLER Q PCH 0.25 POUT UNDERVOLTAGE LOCKOUT
ONA ON ONB REF GND CLK/SEL FB FEEDBACK AND POWER-GOOD SELECT 1.25V REF RDY REFERENCE EN OSCILLATOR 300kHz FEEDBACK PFM/PWM EN OSC Q MODE FB N NCH 0.13 PGND POK* LX
AIN* GAIN BLOCK REF LBP* COMPARATOR N LBN* N
AO*
LBO*
*MAX1701 ONLY
Figure 1. Functional Diagram
_______________Detailed Description
The MAX1700/MAX1701 are highly efficient, low-noise power supplies for portable RF and data acquisition instruments. The MAX1700 combines a boost switching regulator, N-channel power MOSFET, P-channel synchronous rectifier, precision reference, and shutdown control. The MAX1701 contains all of the MAX1700 features plus a versatile gain amplifier, POK output, and a low-battery comparator (Figure 1). The MAX1700/ MAX1701 come in a 16-pin QSOP package, which occupies no more space than an 8-pin SO. The switching DC-DC converter boosts a 1- to 3-cell input to an adjustable output between 2.5V and 5.5V. The MAX1700/MAX1701 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 full-
power operation, as well as low-quiescent current for maximum battery life during standby and shutdown modes. They feature constant-frequency (300kHz), lownoise PWM operation with up to 800mA output capability. See Table 1 for typical available output current. A low-quiescent-current, low-power mode offers an output up to 100mA and reduces quiescent power consumption to 200W. In shutdown mode, the quiescent current is further reduced to just 3A. Figure 2 shows the standard application circuit for the MAX1700/MAX1701. Additional features include synchronous rectification for high efficiency and improved battery life, a POK output, and an uncommitted comparator for low-battery detection (MAX1701). A CLK input allows frequency synchronization to reduce interference. Dual shutdown controls allow shutdown using a momentary pushbutton switch and microprocessor control (MAX1701).
9
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
0.7V TO 5.5V
POUT
22F L1 10H MBR0520L OUT
FB REF
P
R Q N LX
MAX1700 MAX1701
CLK/SEL ONA ONB
LX D1 POUT 10 OUT 0.22F 2x 100F 0.22F
OUTPUT
S
R1 REF 0.22F GND FB PGND FIXED OUTPUT (GND) ADJUSTABLE R2
1.3A CURRENT LIMIT OSC
PGND
Figure 2. Fixed or Adjustable Output (PWM mode).
Figure 3. Simplified PWM Controller Block Diagram
Table 1. Typical Available Output Current
NUMBER OF CELLS 1 NiCd/NiMH 2 NiCd/NiMH 2 NiCd/NiMH 3 NiCd/NiMH or 1 Li-Ion INPUT OUTPUT OUTPUT VOLTAGE (V) VOLTAGE (V) CURRENT (mA) 1.2 2.4 2.4 3.6 3.3 3.3 5.0 5.0 300 750 525 850
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 low-noise PWM or low-power operation, depending on the CLK/SEL pin setting (Table 2).
Table 2. Selecting the Operating Mode
CLK/SEL 0 1 External Clock (200kHz to 400kHz) MODE Low Power PWM Synchronized PWM FEATURES Low supply current Low noise, high output current Low noise, high output current
Low-Noise PWM Operation When CLK/SEL is pulled high, the MAX1700/MAX1701 operate in a higher power, low-noise pulse-widthmodulation (PWM) mode. During PWM operation, they switch at a constant frequency (300kHz) and then modulate the MOSFET switch pulse width to control the power transferred per cycle and regulate the voltage across the load. In PWM mode the devices can output up to 800mA. Switching harmonics generated by fixedfrequency operation are consistent and easily filtered. See the Noise Spectrum Plot in the Typical Operating Characteristics.
During PWM operation, each rising edge of the internal clock 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, slope compensation, and current-feedback 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 to which the inductor current is allowed to ramp during each cycle and modulates the MOSFET switch pulse width. A second comparator enforces an inductor current limit of 1.6A max.
Step-Up Converter
The step-up switching DC-DC converter generates an adjustable output from 2.5V to 5.5V. 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
10
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
Q Q R P ERROR COMPARATOR FB REF R 400mA CURRENT LIMIT D LOGIC HIGH POUT
rectifier current has ramped down to 70mA. This forces operation with a discontinuous inductor current.
MAX1700/MAX1701
LX S Q N
Synchronous Rectifier The MAX1700/MAX1701 feature an internal 250m, Pchannel synchronous rectifier to enhance efficiency. Synchronous rectification provides a 5% efficiency improvement over similar nonsynchronous boost regulators. In PWM mode, the synchronous rectifier is turned on during the second half of each switching cycle. In low-power mode, an internal comparator turns on the synchronous rectifier when the voltage at LX exceeds the boost-regulator output and then turns it off when the inductor current drops below 70mA.
Low-Voltage Start-Up Oscillator
PGND
Figure 4. Controller Block Diagram in Low-Power PFM Mode
Synchronized PWM Operation By applying an external clock to CLK/SEL, the MAX1700/MAX1701 can also be synchronized in PWM mode to a frequency between 200kHz and 400kHz. 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 MAX1700/MAX1701 in a low-power mode. During low-power 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 100mA. The output voltage is typically 1% higher than the output voltage in PWM mode. During PFM operation, the error comparator detects the output voltage falling out of regulation and sets a flipflop, turning on the N-channel MOSFET switch (Figure 4). When the inductor current ramps to the PFM mode current limit (400mA typical) 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 cycle until the energy stored in the inductor is transferred to the output filter capacitor and the synchronous
The MAX1700/MAX1701 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 boost-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. Do not apply full load until the output exceeds 2.4V.
Table 3. On/Off Logic Control
ONA 0 0 1 1 ONB 0 1 0 1 Status On Off On On
Shutdown
The MAX1700/MAX1701 shut down to reduce quiescent current to typically 3A. During shutdown, the reference, low-battery comparator, gain block, and all feedback and control circuitry are off. The boost converter's output drops to one Schottky diode drop below the input. Table 3 shows the control logic with ONA and ONB. Both inputs have trip points near 0.5V OUT with 0.15VOUT hysteresis.
Low-Battery Comparator (MAX1701)
The internal low-battery comparator has uncommitted inputs and an open-drain output (LBO) 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
11
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
0.7V TO 5.5V
POUT REF
L1 D1
MAX1701
LBO LBN
MAX1701
CLK/SEL ONA ONB R3 LBP R4
LX POUT 10 OUT 0.22F VOLTAGE MONITOR LOW-BATTERY MONITOR ARBITRARY VOLTAGE MONITOR R6 10 C3 0.22F C4
R5
0.22F
10k LBP
ARBITRARY VOLTAGE R5
R6 GND
BATTERY VOLTAGE
POK
LBO LBN REF AO GND PGND FB AIN
Figure 7. Detecting Battery Voltages Below 1.25V (MAX1701)
OUTPUT
P
Figure 5. Detecting Battery Voltage Above 1.25V
C5 270k
OUT
POUT LBN
R3
POUT OUT
LBO
MAX1701
R3
LBP REF 0.22F GND
R4
MAX1701
LBO LBN REF 0.22F GND LBP
R4
Figure 8. Using the Low-Battery Comparator for Load Control During Start-Up
Figure 6. Using the Low-Battery Comparator to Sense the Output Voltage (MAX1701)
between the positive battery terminal and GND (Figure 5). The resistor values are then calculated as follows: R3 = R4(VTH/VLBN -1) where VTH is the desired input voltage trip threshold and VLBN = VREF = 1.25V. Since the input bias current into LBP is less than 20nA, R4 can be a large value (such as 270k or less) without sacrificing accuracy. The inputs have a common-mode input range from 0.5V to 1.5V and an input-referred hysteresis of 15mV. The low-battery comparator can also be used to monitor the output voltage, as shown in Figure 6. To set the low-battery threshold to a voltage below the 1.25V reference, insert a resistor divider between REF
12
and LBN and connect the battery to the LBP input through a 10k current-limiting resistor (Figure 7). The equation for setting the resistors for the low-battery threshold is then as follows: R5 = R6(VREF/VLBP -1) where VLBP is the desired voltage threshold. In Figures 5, 6, and 7, LBO goes low for a low-voltage input. The low-battery comparator can be used to check the output voltage or to control the load directly on POUT during start-up (Figure 8). Use the following equation to set the resistor values: R3 = R4(VOUTTH/VLBP - 1) where VOUTTH is the desired output-voltage trip point and VLBP is connected to the reference or 1.25V.
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
Reference
The MAX1700/MAX1701 have an internal 1.250V, 1% bandgap reference. Connect a 0.22F bypass capacitor to GND within 0.2in. (5mm) of the REF pin. REF can source up to 50A of external load current.
Gain Block (MAX1701)
The MAX1701's gain block can function as a third comparator or can be used to build a linear regulator using an external P-channel MOSFET pass device. The gainblock output is a single-stage transconductance amplifier that drives an open-drain N-channel MOSFET. Figure 9 shows the gain block used in a linear regulator. The output of an external P-channel pass element is compared to the internal reference. The difference is amplified and used to drive the gate of the pass element. Use a logic-level PFET such as the Fairchild ). NDS336P (RDS(ON) = 270m If the PFET RDS(ON) is less than 250m, the linear regulator output filter capacitance may need to be increased to above 47F.
MAX1700/MAX1701
Power-OK (MAX1701)
The MAX1701 features a power-good comparator. This comparator's open-drain output (POK) is pulled low when the output voltage falls to 10% below the regulation point.
IN
LX
P 2x 100F 20k
__________________Design Procedure
47F
MAX1701
AO N
Setting the Output Voltages
Set the output voltage between 2.5V and 5.5V by connecting a resistor voltage-divider to FB from OUT to GND, as shown in Figure 2. The resistor values are then as follows: R1 = R2 (VOUT/VFB - 1)
AIN REF R6
R5
Figure 9. Using Gain Block as a Linear Regulator
where VFB, the boost-regulator feedback setpoint, is 1.23V. Since the input bias current into FB is less than 20nA, 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.
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
Inductor Selection
The MAX1700/MAX1701's high switching frequency allows the use of a small surface-mount inductor. A 10H inductor should have a saturation-current rating that exceeds the N-channel switch current limit of 1.6A. However, it is generally acceptable to bias the inductor current into saturation by as much as 20%, although this will slightly reduce efficiency. For high efficiency, choose an inductor with a high-frequency core material (such as ferrite) to reduce core losses. To minimize radiated noise, use a toroid, pot core, or shielded bobbin inductor. Connect the inductor from the battery to the LX pin as close to the IC as possible. See Table 4 for a list of component suppliers and Table 5 for suggested components.
CAPACITORS Matsuo 267 series Sprague 595D series AVX TPS series Sanyo OS-CON series Nichicon PL series DIODES Motorola MBR0520L 1N5817 13
Table 5. Component Selection Guide
PRODUCTION Surface Mount Through Hole INDUCTORS Sumida CDR63B, CD73, CDR73B, CD74B series Coilcraft DO1608, DO3308, DT3316 series Sumida RCH654 series
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
C LX POUT
270k
MAX1701
ONB OUT VDD I/O ONA I/O
ON/OFF
MAX1700
MAX8865/MAX8866 DUAL OR MAX8863/MAX8864 SINGLE LOW-DROPOUT LINEAR REGULATORS
0.1F
PA 270k C RADIO
Figure 10. Momentary Pushbutton On/Off Switch
Figure 11. Typical Phone Application
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, its current rating only needs to be 500mA. Connect the diode between LX and POUT as close to the IC as possible. Do not use ordinary rectifier diodes since slow switching speeds and long reverse recovery times will compromise efficiency and load regulation.
exceed the ripple current ratings of tantalum capacitors. Avoid most aluminum-electrolytic capacitors, since their ESR is often too high.
Bypass Capacitors
Two ceramic bypass capacitors are required for proper operation. Bypass REF with a 0.22F capacitor to GND. Also connect a 0.22F ceramic capacitor from OUT to GND. Each should be placed as close to their respective pins as possible, within 0.2in. (5mm) of the DC-DC converter IC. See Table 4 for suggested suppliers.
Input and Output Filter Capacitors
Choose input and output filter capacitors that will 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. For full output, two 100F, 100m, low-ESR tantalum output filter capacitors are recommended. For loads below 250mA, a single 100F output capacitor will suffice. The input filter capacitor (CIN) reduces peak currents drawn from the input source and reduces input switching noise. The input voltage source impedance determines the required size of the input capacitor. When operating directly from one or two NiCd cells placed close to the MAX1700/MAX1701, use a 22F, low-ESR input filter capacitor. When operating from a power source placed farther away, or from higher impedance batteries such as alkaline or lithium cells, use one or two 100F, 100m, low-ESR tantalum capacitors. Sanyo OS-CON and Panasonic SP/CB-series ceramic capacitors offer the lowest ESR. Low-ESR tantalum capacitors are a good choice and generally offer a good tradeoff between price and performance. Do not
14
__________Applications Information
Push-On/Push-Off Control
A momentary pushbutton switch can be used to turn the MAX1700/MAX1701 on and off. In Figure 10, ONA is pulled low and ONB is pulled high when the part is 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 to exit reset (200ms) and drive ONA high. A small capacitor is added to help debounce the switch. The controller 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 controller to read the switch status and pull ONA low. When the switch is released, ONB is pulled high.
Use in a Typical Wireless Phone Application
The MAX1700/MAX1701 are ideal for use in digital cordless and PCS phones. The power amplifier (PA) is connected directly to the boost-converter output for maximum voltage swing (Figure 11). Low-dropout linear regulators are used for post-regulation to generate
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters
low-noise power for DSP, control, and RF circuitry. Typically, RF phones spend most of their life in standby mode with only short periods in transmit/receive mode. During standby, maximize battery life by setting CLK/SEL = 0; this places the IC in low-power mode (for the lowest quiescent power consumption).
Soft-Start
To implement soft-start, set CLK/SEL low on power-up; this forces low-power operation and reduces the peak switching current to 550mA max. Once the circuit is in regulation and start-up transients have settled, CLK/SEL can be set high for full-power operation.
MAX1700/MAX1701
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 the voltage and current feedback signals. 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. A separate low-noise ground plane containing the reference and signal grounds should only connect to the power-ground plane at one point. This minimizes the effect of powerground currents on the part. Consult the MAX1701 EV kit manual for a layout example. On multilayer boards, do not connect the ground pins of the power components using vias through an internal ground plane. Instead, place them close together and route them in a star-ground configuration using component-side copper. Then use vias to connect the star ground to the internal ground plane. Keep the voltage feedback network very close to the IC, within 0.2in. (5mm) of the FB pins. Keep noisy traces, such as from the LX pin, away from the voltage feedback networks. Separate them with grounded copper. Consult the MAX1700 evaluation kit for a full PC board example.
Intermittent Supply/Battery Connections
When boosting an input supply connected with a mechanical switch, or a battery connected with spring contacts, input power may sometimes be intermittent as a result of contact bounce. When operating in PFM mode with input voltages greater than 2.5V, restarting after such dropouts may initiate high current pulses that interfere with the MAX1700/MAX1701 internal MOSFET switch control. If contact or switch bounce is anticipated in the design, use one of the following solutions. 1) Connect a capacitor (CONB) from ONB to VIN, a 1M resistor (RONB) from ONB to GND, and tie ONA to GND (Figure 12). This RC network differentiates fast input edges at VIN and momentarily holds the IC off until VIN settles. The appropriate value of CONB is 10-5 times the total output filter capacitance (COUT), so a COUT of 200F results in CONB = 2nF. 2) Use the system microcontroller to hold the MAX1700/MAX1701 in shut down from the time when power is applied (or reapplied) until the output capacitance (COUT) has charged to at least the input voltage. Power-on reset times of tens of milliseconds accomplish this. 3) Ensure that the IC operates, or at least powers up, in PWM mode (CLK/SEL = high). Activate PFM mode only after the VOUT has settled and all of the system's poweron reset flags are cleared.
Pin Configurations (continued)
TOP VIEW
LBP 1 LBN 2 REF 3 CLK/SEL 4 GND 5 POK 6 ONB 7 ONA 8 16 LBO 15 POUT 14 OUT RONB 1M 8 ONA CONB 2nF LX 7 ONB OUT 13 14 COUT 200F
MAX1701
13 LX 12 PGND 11 FB 10 AIN 9 AO
MAX1700 MAX1701
POUT
15
QSOP
Figure 12. Connecting CONB and RONB when Switch or Battery-Contact Bounce Is Anticipated
15
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1-Cell to 3-Cell, High-Power (1A), Low-Noise, Step-Up DC-DC Converters MAX1700/MAX1701
Chip Information
TRANSISTOR COUNT: 531 SUBSTRATE CONNECTED TO GND
________________________________________________________Package Information
QSOP.EPS
16
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