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19-1698; Rev 1; 2/01
1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
General Description
The MAX1763 is a high-efficiency, low-noise, step-up DC-DC converter intended for use in battery-powered wireless applications. This device maintains exceptionally low quiescent supply current (110A) despite its high 1MHz operating frequency. Small external components and a tiny package make this device an excellent choice for small hand-held applications that require the longest possible battery life. The MAX1763 uses a synchronous-rectified pulsewidth-modulation (PWM) boost topology to generate 2.5V to 5.5V outputs from a wide range of input sources, such as one to three alkaline or NiCd/NiMH cells or a single Lithium-ion (Li+) cell. Maxim's proprietary Idle ModeTM circuitry significantly improves efficiency at light load currents while smoothly transitioning to fixed-frequency PWM operation at higher load currents to maintain excellent full-load efficiency. Lownoise, forced-PWM mode is available for applications that require constant-frequency operation at all load currents. The MAX1763 may also be synchronized to an external clock to protect sensitive frequency bands in communications equipment. The MAX1763 includes an on-chip linear gain block that can be used to build a high-power external linear regulator or as a low-battery comparator. Soft-start and current limit functions permit optimization of efficiency, external component size, and output voltage ripple. The MAX1763 is available in a space-saving 16-pin QSOP package or a high-power (1.5W) 16-pin TSSOPEP package. o Up to 94% Efficiency o +0.7V to +5.5V Input Voltage Range o 1.1V Guaranteed Startup Input Voltage o Up to 1.5A Output o Fixed 3.3V Output or Adjustable (2.5V to 5.5V) o 1MHz PWM Synchronous-Rectified Topology o 1A Logic-Controlled Shutdown o Analog Gain Block for Linear-Regulator or LowBattery Comparator o Adjustable Current Limit and Soft-Start o 1.5W TSSOP Package Available
Features
MAX1763
________________________Applications
Digital Cordless Phones PCS Phones Wireless Handsets Hand-Held Instruments Palmtop Computers Personal Communicators
Ordering Information
PART MAX1763EEE MAX1763EUE TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 16 QSOP 16 TSSOP-EP*
Typical Operating Circuit
IN 0.7V TO 5.5V 1.5H
*EP = Exposed pad Idle Mode is a trademark of Maxim Integrated Products.
Pin Configuration
OUT 3.3V AT 1.5A
TOP VIEW
ONA 1 ISET 2 16 ONB 15 POUT 14 LX
LX POUT OFF ON PWM OR NORMAL LBI OR GAIN BLOCK INPUT MAX1763 ON OFF ONB ONA CLK/SEL AIN ISET REF FB GND AO PGND OUT
REF 3 GND 4 FB 5 OUT 6 AIN 7
LBO OR GAIN BLOCK OUTPUT
MAX1763
13 POUT 12 PGND 11 LX 10 PGND 9 CLK/SEL
AO 8
QSOP TSSOP-EP
________________________________________________________________ Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
ABSOLUTE MAXIMUM RATINGS
ONA, ONB, AO, OUT to GND.......................................0.3V, +6V PGND to GND.....................................................................0.3V LX to PGND ............................................-0.3V to (VPOUT + 0.3V) CLK/SEL, REF, FB, ISET, POUT, AIN to GND.........................................-0.3V to (VOUT + 0.3V) POUT to OUT ......................................................................0.3V Continuous Power Dissipation 16-Pin QSOP (derate 8.7mW/C above +70C)...........667mW 16-Pin TSSOP-EP (derate 19mW/C above +70C) ...........1.5W Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+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 = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.)
PARAMETER DC-DC CONVERTER Input Voltage Range (Note 1) Minimum Startup Voltage (Note 2) Temperature Coefficient of Startup Voltage Frequency in Startup Mode Internal Oscillator Frequency Oscillator Maximum Duty Cycle (Note 3) External Clock Frequency Range Output Voltage FB Regulation Voltage FB Input Current Load Regulation Output Voltage Adjust Range Output Voltage Lockout Threshold (Note 4) ISET Input Leakage Current Supply Current in Shutdown No-Load Supply Current, LowPower Mode (Note 5) No-Load Supply Current, LowNoise Mode Gain Block Supply Current Rising edge VISET = 1.25V V ONB = 3.6V, VONA = 0 CLK/SEL = GND, AIN = OUT CLK/SEL = OUT VAIN < (VOUT - 1.4V), gain block enabled VFB < 0.1V, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A Adjustable output, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A VFB = 1.35V CLK/SEL = OUT, 0 < ILX < 1.1A 2.5 2.00 2.15 0.01 1 110 2.5 25 50 ILOAD < 1mA, TA = +25C ILOAD < 1mA VOUT = 1.5V CLK/SEL = OUT 125 0.8 80 0.5 3.17 1.215 3.3 1.245 0.01 -1.0 5.5 2.30 50 10 200 0.7 0.9 -2 500 1 86 1000 1.2 90 1.2 3.38 1.270 100 5.5 1.1 V V mV/C kHz MHz % MHz V V nA % V V nA A A mA A CONDITIONS MIN TYP MAX UNITS
2
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, 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 N-Channel Current Limit P-Channel Turn-Off Current REFERENCE Reference Output Voltage Reference Load Regulation Reference Supply Rejection GAIN BLOCK AIN Reference Voltage AIN Input Current Transconductance AO Output Low Voltage AO Output High Leakage Gain-Block Enable Threshold (VOUT - VAIN) (Note 6) Gain-Block Disable Threshold (VOUT - VAIN) (Note 6) LOGIC INPUTS CLK/SEL Input Low Level CLK/SEL Input High Level ONA and ONB Input Low Level (Note 7) ONA and ONB Input High Level (Note 7) Input Leakage Current Minimum CLK/SEL Pulse Width Maximum CLK/SEL Rise/Fall Time 2.5V VOUT 5.5V 2.5 V VOUT 5.5V 1.1 V VOUT 1.8V 1.8 V VOUT 5.5V 1.1 V VOUT 1.8V 1.8 V VOUT 5.5V CLK/SEL, ONA, ONB VOUT - 0.2V 1.6 0.01 100 100 1 A ns ns (0.8) VOUT 0.2 0.4 (0.2) VOUT V V V 0.2 IAO = 20A VAIN = 1.5V VAO = 1V, 10A < IAO < 100A VAIN = 0.5V, IAO = 100A VAIN = 1.5V, VAO = 5.5V 5 910 938 0.01 10 0.1 0.01 970 30 16 0.4 1 1.4 mV nA mS V A V V IREF = 0 -1A < IREF < 50A 2.5V < VOUT < 5V 1.230 1.250 5 0.2 1.270 15 5 V mV mV CLK/SEL = GND VLX = 0, VOUT = 5.5V VLX = V ONB = VOUT = 5.5V, VONA = 0 N channel P channel 2.0 10 0.1 0.1 0.075 0.13 2.5 120 10 10 0.13 0.25 3.4 240 A A A mA CONDITIONS MIN TYP MAX UNITS
MAX1763
V
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
ELECTRICAL CHARACTERISTICS
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 8)
PARAMETER DC-DC CONVERTER Input Voltage Range (Note 1) Minimum Startup Voltage (Note 2) Frequency in Startup Mode Internal Oscillator Frequency Oscillator Maximum Duty Cycle (Note 3) External Clock Frequency Range Output Voltage FB Regulation Voltage FB Input Current Output Voltage Adjust Range Output Voltage Lockout Threshold (Note 4) ISET Input Leakage Current Supply Current in Shutdown No-Load Supply Current, LowPower Mode (Note 5) Gain Block Supply Current DC-DC SWITCHES POUT Leakage Current LX Leakage Current Switch On-Resistance N-Channel Current Limit P-Channel Turn-Off Current REFERENCE Reference Output Voltage Reference Load Regulation Reference Supply Rejection GAIN BLOCK AIN Reference Voltage AIN Input Current Transconductance AO Output Low Voltage AO Output High Leakage IAO = 20A VAIN = 1.5V VAO = 1V, 10A < IAO < 100A VAIN = 0.5V, IAO = 100A VAIN = 1.5V, VAO = 5.5V 5 910 970 30 16 0.4 1 mV nA mS V A IREF = 0 -1A < IREF < 50A 2.5V < VOUT < 5V 1.220 1.270 15 5 V mV mV CLK/SEL = GND VLX = 0, VOUT = 5.5V VLX = V ONB = VOUT = 5.5V, VONA = 0 N-channel P-channel 2.0 10 10 10 0.13 0.25 3.4 240 A A A mA Rising edge VISET = 1.25V V ONB = 3.6V, VONA = 0 CLK/SEL = GND, AIN = OUT VAIN < (VOUT - 1.4V), gain block enabled VFB < 0.1V, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A Adjustable output, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A VFB = 1.35V 2.5 2.00 ILOAD < 1mA, TA = +25C VOUT = 1.5V CLK/SEL = OUT 125 0.75 80 0.6 3.17 1.215 5.5 1.1 1000 1.25 91 1.2 3.38 1.270 100 5.5 2.30 50 10 200 50 V V kHz MHz % MHz V V nA V V nA A A A CONDITIONS MIN MAX UNITS
4
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40C to +85C, unless otherwise noted.) (Note 8)
PARAMETER LOGIC INPUTS Gain-Block Enable Threshold (VOUT - VAIN) (Note 6) Gain-Block Disable Threshold (VOUT - VAIN) (Note 6) CLK/SEL Input Low Level CLK/SEL Input High Level ONA and ONB Input Low Level (Note 7) ONA and ONB Input High Level (Note 7) Input Leakage Current 2.5 V VOUT 5.5V 2.5 V VOUT 5.5V 1.1 V VOUT 1.8V 1.8 V VOUT 5.5V 1.1 V VOUT 1.8V 1.8V VOUT 5.5V CLK/SEL, ONA, ONB VOUT - 0.2V 1.6 1 A (0.8) VOUT 0.2 0.4 0.2 (0.2) VOUT 1.4 V V V V V CONDITIONS MIN MAX UNITS
MAX1763
V
Note 1: Operating voltage. Because the regulator is bootstrapped to the output, once started, the MAX1763 will operate down to 0.7V input. Note 2: Startup is tested with the circuit of Figure 2. Note 3: Defines low-noise mode maximum step-up ratio. Note 4: The regulator is in startup mode until this voltage is reached. Do not apply full load current until the output exceeds 2.3V. Note 5: Supply current from the 3.3V output is measured between the 3.3V 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. The gain block is disabled. Note 6: Connect AIN to OUT to disable gain block. Note 7: ONA and ONB have hysteresis of approximately 0.15 VOUT. Note 8: Specifications to -40C are guaranteed by design and not production tested.
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Typical Operating Characteristics
(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V)
MAX1763 toc01
EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V)
MAX1763 toc02
MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE
MAX1763 toc03
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0.001 0.01 0.1 1 A: VIN = 2.4V B: VIN = 1.2V C: VIN = 0.9V = NORMAL MODE = FPWM MODE C B A
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 A: VIN = 3.6V B: VIN = 2.4V C: VIN = 1.2V = NORMAL MODE = FPWM MODE 0.001 0.01 0.1 1 C A B
3.0 2.5 OUTPUT CURRENT (A) 2.0 1.5 1.0 0.5 0 VOUT = 5V VOUT = 3.3V
10
10
0.8
1.6
2.4 INPUT VOLTAGE (V)
3.2
4.0
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
NO-LOAD INPUT vs. INPUT VOLTAGE
= INPUT VOLTAGE INCREASING = INPUT VOLTAGE DECREASING
MAX1763 toc04
SHUTDOWN CURRENT vs. INPUT VOLTAGE
MAX1763 toc05
INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE
1.15 1.10 FREQUENCY (MHz) 1.05 1.00 0.95 0.90 0.85 VIN = 3.6V, VOUT = 5V VIN = 2.4V, VOUT = 3.3V
MAX1763 toc06
0.1
10
1.20
0.01
SHUTDOWN CURRENT (A)
INPUT CURRENT (A)
1
0.001
0.0001 0 1 2 3 4 5 INPUT VOLTAGE (V)
0.1 0 1 2 3 4 5 6 INPUT VOLTAGE (V)
0.80 -40 -15 10 35 60 85 TEMPERATURE (C)
STARTUP VOLTAGE vs. OUTPUT CURRENT
MAX1763 toc07
PEAK INDUCTOR CURRENT vs. VISET
MAX1763 toc08
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1763 toc09
4.1 3.6 STARTUP VOLTAGE (V) 3.1 2.6 2.1 1.6 1.1 0.6 0.001
3.0 PEAK INDUCTOR CURRENT (A) 2.5 2.0 1.5 1.0
A
B
C 0.5 0
0.01
0.1
1
10
0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
OUTPUT CURRENT (A)
ISET VOLTAGE (V)
400ns/div VIN = 2.4V, VOUT = 3.3V, IOUT = 1.5A A: INDUCTOR CURRENT, 500mA/div B: VLX, 2V/div C: VOUT, 100mV/div, AC COUPLED
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25C, unless otherwise noted.)
LIGHT-LOAD SWITCHING WAVEFORMS
MAX1763 toc10
MAX1763
LOAD-TRANSIENT RESPONSE
MAX1763 toc11
LINE-TRANSIENT RESPONSE
MAX1763 toc12
A A B
A
C
B B
200ns/div VIN = 1.1V, VOUT = 3.3V, IOUT = 20mA A: LX NODE, 5V/div B: INDUCTOR CURRENT, 0.1A/div, AC COUPLED C: OUTPUT RIPPLE, 0.1V/div, AC COUPLED
100s/div VIN = 2.4V, VOUT = 3.3V, IOUT = 0.2A TO 1.35A A: IOUT, 0.5A/div B: VOUT, 100mV/div, AC-COUPLED
40s/div VIN = 2.4V TO 1.4V, IOUT = 70mA A: VIN, 1V/div B: VOUT, 5mV/div, AC-COUPLED
POWER-ON DELAY
MAX1763 toc13
STARTUP WAVEFORMS NO SOFT-START
MAX1763 toc14
ONA 5V/div
VOUT 2V/div
VOUT 2V/div
IIN 1A/div
IIN 0.5A/div 100s/div
IL = 10mA
ONA 5V/div 2ms/div VIN = 1.2V, VOUT = 3.3V, RLOAD = 3k
STARTUP WAVEFORMS USING SOFT-START
MAX1763 toc15
NOISE SPECTRUM
VIN = 2.4V VOUT = 3.3V
MAX1763 toc16
8
VOUT 2V/div
6 NOISE (mVRMS)
4
IIN 1A/div
2
ONA 5V/div 2ms/div VIN = 1.2V, VOUT = 3.3V, RSS = 510k, CSS = 0.1F, RLOAD = 3k
0
0.01
0.1
1
10
FREQUENCY (MHz)
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Pin Description
PIN 1 NAME ONA FUNCTION On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal operation (Table 3). N-Channel Current Limit Control. For maximum current limit, connect to REF. To reduce current, supply a voltage between REF and GND by means of a resistive voltage-divider. If soft-start is desired, connect a capacitor from ISET to GND. When ONA = low and ONB = high, or VREF < 80% of nominal value, an on-chip switched resistor (100k typ) discharges this pin to GND. 1.250V Voltage Reference Bypass Pin. Connect a 0.22F ceramic bypass capacitor to GND. Up to 50A of external REF load current is allowed. Ground. Connect to PGND with short trace. DC-DC Converter Feedback Input. To set fixed output voltage of +3.3V, connect FB to ground. For adjustable output of 2.5V to 5.5V, connect to a resistive divider placed from OUT to GND. FB set point is 1.245V (Figure 6). IC Power, Supplied from the Output. Bypass to GND with a 1.0F ceramic capacitor, and connect to POUT with a series 4.7 resistor (Figure 2). Gain-Block Input. The nominal transconductance from AIN to AO is 10mS. An external P-channel pass device can be used to build a linear regulator. The gain block can also be used as a low-battery comparator with a threshold of 0.938V. The gain block and its associated quiescent current are disabled by connecting AIN to OUT. Gain-Block Output. This open-drain N-channel output sinks current when VAIN < (0.75)(VREF). AO is high-Z when the device is shut down, or when AIN = OUT. Clock Input for the DC-DC Converter. Also serves to program the operating mode of the switcher as follows: CLK/SEL = LO: Normal; operates at a fixed frequency, automatically switching to low-power mode if load is minimized. CLK/SEL = HI: Forced PWM mode; operates in low-noise, constant-frequency mode at all loads. CLK/SEL = Clocked: Forced PWM mode with the internal oscillator synchronized to CLK in 500kHz to 1200kHz range. Source of N-Channel Power MOSFET Switch. Connect both PGND pins together close to the device. Inductor Connection. Connect the LX pins together close to the device. Power Output. P-channel synchronous rectifier source. Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal operation (Table 3).
2
ISET
3 4 5
REF GND FB
6
OUT
7
AIN
8
AO
9
CLK/SEL
10, 12 11, 14 13, 15 16
PGND LX POUT ONB
Detailed Description
The MAX1763 is a highly-efficient, low-noise power supply for portable RF and hand-held instruments. It combines a boost switching regulator, N-channel power MOSFET, P-channel synchronous rectifier, precision reference, shutdown control, and a versatile gain block (Figure 1). The DC-DC converter boosts a one-cell to three-cell battery voltage input to a fixed 3.3V or adjustable volt8
age between 2.5V and 5.5V. An external Schottky diode is required for output voltages greater than 4V. The MAX1763 guarantees startup with an input voltage as low as 1.1V and remains operational down to an input of just 0.7V. It is optimized for use in cellular phones and other applications requiring low noise and low quiescent current for maximum battery life. It features constant-frequency (1MHz), low-noise PWM operation with up to 1.5A output capability. A CLK input allows frequency synchronization to control the output
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
UNDERVOLTAGE LOCKOUT OUT IC POWER 2.15V EN STARTUP OSCILLATOR Q D CONTROLLER Q P LX ONA ON ONB REF GND CLK/SEL FB ISET AIN GAIN BLOCK 0.938V DUAL MODE/ FB 1.25V REF RDY REFERENCE EN 1MHz OSCILLATOR MODE FB ISET EN OSC Q N PGND POUT
MAX1763
N
AO
Figure 1. Functional Diagram
Table 1. Typical Available Output Current
NUMBER OF CELLS 1 NiCd/NiMH 2 NiCd/NiMH 2.4 1 Li+ 1 Li+ 3 NiCd/NiMH 2.7 (min) 2.7 (min) 3.6 5.0 3.3 5.0 5.0 950 1300 1100 1600
ISET REF C3 0.22F PGND GND ONB
VIN 0.7V TO 5.5V
INPUT VOLTAGE (V) 1.2 2.4
OUTPUT VOLTAGE (V) 3.3 3.3
OUTPUT CURRENT (mA) 675 1500
CLK/SEL ONA
L1 1.5H MBR0520L LX D1 POUT R5 4.7 OUT AIN AO FB C2 1.0F OUT 3.3V C4 2 x 100F
C1 47F
MAX1763
noise spectrum. See Table 1 for typical available output current. In its normal mode of operation (CLK/SEL = low), the MAX1763 offers fixed-frequency PWM operation through most of its load range. At light loads (less than 25% of full load), the device automatically optimizes efficiency by switching only as needed to supply the load. Shutdown reduces quiescent current to just 1A. Figure 2 shows the standard application circuit for the MAX1763. (An external Schottky diode is needed for output voltages greater than 4V, or to assist low-voltage startup.)
NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.
Figure 2. PFM/PWM Automode Connection
Additional features include synchronous rectification for high efficiency and increased battery life, and a gain block that can be used to build a linear regulator using an external P-channel MOSFET pass device. This gain
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Table 2. Selecting the Operating Mode
CLK/SEL MODE Normal operation FEATURES High efficiency at all loads. Fixed frequency at all but light loads. Low noise, fixed frequency at all loads. Low noise, fixed frequency at all loads.
Synchronized-PWM Operation
In a variation of forced-PWM mode, the MAX1763 can be synchronized to an external frequency by applying a clock signal to CLK/SEL. This allows the user to choose an operating frequency (from 500kHz to 1.2MHz) to avoid interference in sensitive applications. For the most noise-sensitive applications, limit the external synchronization signal duty cycle to less than 10% or greater than 90%. This eliminates the possibility that noise from the power switching will coincide with the synchronization signal. If the synchronization signal edge falls on the power switching edge, a slight frequency jitter may occur.
0
1 External clock 500kHz to 1.2MHz
Forced PWM Synchronized PWM
block can also function as a voltage-monitoring comparator. The MAX1763 is available in a 16-pin QSOP package or a 1.5W 16-pin TSSOP-EP package for hightemperature or high-dissipation applications.
Synchronous Rectifier
The MAX1763 features an internal 130m P-channel synchronous rectifier to enhance efficiency. Synchronous rectification provides a 5% efficiency improvement over similar boost regulators that rely on diode rectifiers. 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 turns it off when the inductor current drops below 120mA. When setting output voltages greater than 4V, an external 0.5A Schottky diode must be connected in parallel with the on-chip synchronous rectifier.
Step-Up Converter
During DC-DC converter operation, the internal N-channel MOSFET switch turns on for the first part of each cycle, allowing current to ramp up in the inductor and store energy in a magnetic field. During the second part of each cycle, the MOSFET turns off and inductor current flows through the synchronous rectifier to the output filter capacitor and the load. As the energy stored in the inductor is depleted, the current ramps down and the synchronous rectifier turns off, the Nchannel FET turns on, and the cycle repeats. At light loads, depending on the CLK/SEL pin setting, output voltage is regulated using either PWM or by switching only as needed to service the load (Table 2).
Low-Voltage Startup Oscillator
The MAX1763 uses a CMOS low-voltage startup oscillator for a 1.1V guaranteed minimum startup input voltage. At startup, the low-voltage oscillator switches the N-channel MOSFET until the output voltage reaches 2.15V. Above this level, the normal feedback and control circuitry take over. Once the device is in regulation, it can operate down to 0.7V input because internal power for the IC is derived from the output through the OUT pin. Do not apply full system load until the output exceeds 2.3V.
Normal Operation
Pulling CLK/SEL low selects the MAX1763's normal operating mode. In this mode, the device operates in PWM when driving medium to heavy loads, and at light loads only, switches as needed. This optimizes efficiency over the widest range of load conditions. In normal operation mode, the output voltage regulates 1% higher than in forced-PWM mode. See Efficiency vs. Load Current in the Typical Operating Characteristics section.
Shutdown, ONA, ONB
ONA and ONB turn the MAX1763 on or off. When ONA = 1 or ONB = 0, the device is on. When ONA = 0 and ONB = 1, the device is off (Table 3). Logic high ON control can be implemented by connecting ONB high and using ONA for the control input. Momentary onepushbutton ON/OFF control is described in the Applications Information section. Both ONA and ONB have approximately (0.15 VOUT)V of hysteresis.
Forced-PWM Operation
When CLK/SEL is high, the MAX1763 operates in a lownoise forced-PWM mode. During forced-PWM operation, the MAX1763 switches at a constant frequency (1MHz) and modulates the MOSFET switch pulse width to control the power transferred per cycle and regulate the output voltage. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. See the Noise Spectrum plot in the Typical Operating Characteristics.
10
Reference
The MAX1763 has an internal 1.250V reference. Connect a 0.22F ceramic bypass capacitor to GND
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Table 3. On/Off Logic Control
ONA 0 0 1 1
TO VIN OR VOUT R3 AIN R4
R4 100k ISET REF C3 0.22F PGND FB GND
ONB 0 1 0 1
MAX1763 On Off On On
AO CLK/SEL ONB LX VIN
RG 20k 2.5V 1.5H C1 47F COUT 47F
3.3V MBRO520L C4 220F
POUT R5 4.7 C2 1F
POUT R6 150k MAX1763 AO POWER-OK OUTPUT
MAX1763
R3 165k ONA OUT
AIN
Figure 3. Using the Gain Block as a Power-OK Comparator
VIN 1.8V TO 5.5V
L1 1.5H
C1 47F
BOOST OUTPUT LINEARREGULATED OUTPUT COUT 47F
Figure 5. Powering a Gain-Block Linear Regulator from the Input Voltage
CLK/SEL ONA
LX POUT R5 4.7 C4 220F RG 20k
P
MAX1763
R3 ONB OUT
AIN
C2 1.0F
R4 0.22F
ISET REF PGND
AO FB GND
R1 SIGNAL GROUND POWER GROUND
R2 30k
using an external P-channel MOSFET pass device. The gain-block output is a single-stage transconductance amplifier that drives an open-drain N-channel MOSFET. The transconductance (GM) of the entire gain-block stage is 10mS. The internal gain block amplifies the difference between AIN and the internal 0.938V reference. To provide a power-OK signal, connect the gain-block input, AIN, to an external resistor-divider (Figure 3). The input bias current into AIN is less than 30nA, allowing large-value divider resistors without sacrificing accuracy. Connect the resistor voltage-divider as close to the IC as possible, within 0.2in (5mm) of AIN. Choose an R4 value of 270k or less, then calculate R3 using: R3 = R4((VTRIP / VAIN ) - 1) where VAIN is 0.938V. Figures 4 and 5 show the gain block used in a linearregulator application. The output of an external P-channel pass element is compared to an internal 0.938V reference. The difference is amplified and drives the gate of the pass element. Use a logic-level PFET, such as Fairchild's NDS336P (RDS(ON) = 270m). When the linear-regulator output voltage is in regulation, the MOSFET will not be full on; thus, the on-resistance will not be important. However, if the linear regulator is used
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Figure 4. Using the Gain Block as a Linear Regulator from the Boosted Output Voltage
within 0.2in (5mm) of the REF pin. REF can source up to 50A of external load current.
Gain Block
The MAX1763 gain block can function as a power-OK comparator or can be used to build a linear regulator
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
in dropout, the MOSFET on-resistance will determine the dropout voltage (VDROPOUT = IOUT RDS(ON)). If a lower RDS(ON) PFET is used, increase the linear-regulator output filter capacitance to maintain stability. The output capacitance can be determined by the function: COUT [ (VREF / VOUT) GM GFS CG (RG 2) ] and COUT 10 [ (VREF / [VOUT GBP]) GM GFS RG ] where VREF is the 0.983V reference voltage, GM is the 10mS internal amplifier transconductance, GFS is the external MOSFET transconductance, RG is the gatesource resistor, and GBP is the gain-bandwidth product of the internal gain block, 63Mrad/s.
MAX1763
OUT R1 FB R2
MAX1763
R1 = R2
( VV - 1), V
OUT FB
FB = 1.245V, R2 30k
Figure 6. Connecting Resistors for External Feedback
REF 0.22F RSS MAX1763
___________________Design Procedure
Setting the Output Voltage
For a fixed 3.3V output, connect FB to GND. To set the output voltage between 2.5V and 5.5V, connect a resistor voltage-divider to FB from OUT to GND (Figure 6). The input bias current into FB is less than 100nA, allowing large-value divider resistors without sacrificing accuracy. Connect the resistor voltage-divider as close to the IC as possible, within 0.2in (5mm) of FB. Choose R2 of 30k or less, then calculate R1 using: R1 = R2((VOUT / VFB ) - 1) where VFB, the boost-regulator feedback set point, is 1.245V.
ISET CSS ILIM = 2.5A tSS = RSS CSS
Figure 7. Soft-Start with Maximum Switch Limit Current
REF 0.22F RSS1 ISET RSS2 CSS ILIM = 2.5A MAX1763
Setting the Switch Current Limit and Soft-Start
The ISET pin adjusts the inductor peak current and can also be used to implement soft-start. With ISET connected to REF, the inductor current limits at 2.5A. With ISET connected to a resistive divider set from REF to GND, the current limit is reduced according to: ILIM = 2.5(VISET / 1.25) [A] Implement soft-start by placing a resistor from ISET to REF (>300k) and a capacitor from ISET to GND. In shutdown, ISET is discharged to GND through an internal 100k resistor. As the capacitor voltage rises, the output current is allowed to increase, and the output voltage rises. The speed at which the output rises is determined by the soft-start time constant: tSS = RSS CSS where RSS 300k. Both features may be implemented simultaneously by placing a capacitor across the lower resistor of the current-limiting resistive divider (Figures 7 and 8).
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(R
RSS2
SS1 + RSS2
)
tSS = (RSS1 RSS2)CSS
Figure 8. Soft-Start with Reduced Switch Limit Current
Package Selection
The MAX1763 is available in two packages, a 16-pin QSOP and a 16-pin TSSOP-EP. Since the MAX1763 has excellent efficiency, most applications are well served by the QSOP package. If the application requires high power dissipation, or operation in a high ambient temperature, choose the TSSOP-EP package. The TSSOP-EP is equipped with an exposed metal pad on its underside for soldering to grounded circuit board copper. This reduces the junction-to-case thermal
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Table 4. Component Selection Guide
INDUCTORS Coilcraft LPT3305 Sumida CAPACITORS AVX TPS series Kemet T510 series Sanyo POSCAP series Panasonic SP/CB Nihon EP10QY03 Motorola MBR0520L DIODES AVX Coilcraft Kemet Motorola Sumida
Table 5. Component Suppliers
SUPPLIER PHONE USA: 843-448-9411 USA: 847-639-6400 USA: 810-287-2536 USA: 408-629-4789 Japan: 81-45-474-7030 USA: 847-956-0666 Japan: 011-81-3-3667-3302
resistance of the package from +115C/W for QSOP to +53C/W for the TSSOP-EP. At an ambient temperature of +70C, continuous power dissipation for the QSSOP package is 667mW, while the TSSOP-EP can dissipate 1.5W. A first-order estimate of power dissipation can be determined by calculating the output power delivered to the load (e.g., 3.3V 1A = 3.3W). At the input voltage used, find the efficiency from the Typical Operating Characteristics graphs (e.g., 87%). The estimated power dissipation in the MAX1763 is then: (100% - %Efficiency) Output Power. The example would have: 13% 3.3W = 0.43W, allowing the QSOP package (667mW) to be used. For higher ambient temperature, higher output power, or a lower-efficiency operating point, the TSSOP-EP package (1.5W) may be necessary. For detailed package mechanical information, see the package outline drawings at the end of this data sheet.
Note: Please indicate that you are using the MAX1763 when contacting these component suppliers.
generic 1N5817. This external diode is also recommended for applications that must start with input voltages at or below 1.8V. The Schottky diode carries current during both startup and after the synchronous rectifier turns off. Thus, its current rating only needs to be 500mA even if the inductor current is higher. Connect the diode as close to the IC as possible. Do not use ordinary rectifier diodes; their slow switching speeds and long reverse-recovery times render them unacceptable. For circuits that do not require startup with inputs below 1.8V, and have an output of 4V or less, no external diode is needed.
Input and Output Capacitors
Choose input and output 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. A 220F, low equivalent-series-resistance (ESR) (less than 100m) capacitor is recommended for most applications. Alternatively, two 100F capacitors in parallel will reduce the effective ESR for even better performance. The input capacitor reduces peak currents drawn from the input source and also reduces input switching noise. The input voltage source impedance determines the required size of the input capacitor. When operating directly from one or two NiMH cells placed close to the MAX1763, use a single 47F low-ESR input filter capacitor. With higher impedance batteries, such as alkaline and Li+, a higher value input capacitor may improve efficiency. Sanyo POSCAP, Panasonic SP/CB, and Kemet T510 are good low-ESR capacitors (Tables 4 and 5). LowESR tantalum capacitors offer a good trade-off between price and performance. Do not exceed the ripple current ratings of tantalum capacitors. Avoid aluminum
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Inductor Selection
The MAX1763's high switching frequency allows the use of a small 1.5H surface-mount inductor. The chosen inductor should generally have a saturation current rating exceeding the N-channel switch current limit; however, it is acceptable to bias the inductor current into saturation by as much as 20% if a slight reduction in efficiency is acceptable. Inductors rated for lower peak current may be used if ISET is employed to reduce the peak inductor current (see Setting the Switch Current Limit and Soft-Start). For high efficiency, choose an inductor with a high-frequency ferrite core material to reduce core losses. To minimize radiated noise, use a toroid or shielded inductor. See Table 4 for suggested components and Table 5 for a list of component suppliers. Connect the inductor from the battery to the LX pins as close to the IC as possible.
External Diode
For output voltages greater than 4V, an external Schottky diode must be connected from LX to POUT, in parallel with the on-chip synchronous rectifier (Figure 2). The diode should be rated for 0.5A. Representative devices are Motorola MBR0520L, Nihon EP05Q03L, or
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
electrolytic capacitors; their high ESR typically results in higher output ripple voltage.
Bypass Components
A few ceramic bypass capacitors are required for proper operation. Bypass REF to GND with 0.22F. Also, bypass OUT to GND with a 1F ceramic capacitor, and connect OUT to POUT with a 4.7 resistor. Each of these components should be placed as close to their respective IC pins as possible, within 0.2in (5mm). Table 5 lists suggested suppliers.
Additionally, the ground pin (GND) also channels heat. Connect the exposed thermal pad and GND to circuit ground by using a large pad or multiple vias to the ground plane.
Step-Up/Step-Down Applications
In some battery-powered applications, the battery voltage range overlaps the output voltage. In this case, depending on the battery voltage, the regulator will have to step the voltage up or down. To make a stepup/step-down regulator, use the gain block to make a linear regulator that follows the step-up converter. In this case, if the battery voltage is low, then the circuit will step up, and when the battery voltage is high, the linear regulator will drop the voltage. See the Gain Block section on how to use the gain block to make a linear regulator. When the output voltage is greater than the regulation voltage, then the synchronous rectifier will be held on, reducing the dropout, and thus increasing the efficiency when the battery voltage is close to, but slightly above, the regulation voltage.
Layout Considerations
High switching frequencies and large peak currents make PC board layout a critical part of design. Poor design will cause excessive EMI and ground bounce, 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, and filter capacitors, should be placed as close together as possible, and their traces should be kept short, direct, and wide. Keep the voltage feedback network very close to the IC, within 0.2in (5mm) of the FB pins. Keep noisy traces, such as those from the LX pin, away from the voltage feedback networks and guarded from them using grounded copper. If an external rectifier is used, its traces must be kept especially short and use an absolute minimum of copper area to avoid excess capacitance that can slow the operation of the on-chip synchronous rectifier and actually reduce efficiency. Refer to the MAX1763 EV kit for a full PC board example. The MAX1763 TSSOP-EP package features an exposed thermal pad on its underside. This pad lowers the package's thermal resistance by providing a direct thermal heat path from the die to the PC board.
Chip Information
TRANSISTOR COUNT: 1530 SUBSTRATE CONNECTED TO GND
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter
Package Information
QSOP.EPS
MAX1763
Note: The MAX1763EEE is a 16-pin QSOP and does not have a heat slug. Use the MAX1763EUE for higher power dissipation.
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1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763
Package Information (continued)
TSSOP, 4.0,EXP PADS.EPS
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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