19-1698; Rev 1; 2/01 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter The MAX1763 is available in a space-saving 16-pin QSOP package or a high-power (1.5W) 16-pin TSSOPEP package. Typical Operating Circuit Features ♦ Up to 94% Efficiency ♦ +0.7V to +5.5V Input Voltage Range ♦ 1.1V Guaranteed Startup Input Voltage ♦ Up to 1.5A Output ♦ Fixed 3.3V Output or Adjustable (2.5V to 5.5V) ♦ 1MHz PWM Synchronous-Rectified Topology ♦ 1µA Logic-Controlled Shutdown ♦ Analog Gain Block for Linear-Regulator or LowBattery Comparator ♦ Adjustable Current Limit and Soft-Start ♦ 1.5W TSSOP Package Available ________________________Applications Digital Cordless Phones Hand-Held Instruments PCS Phones Palmtop Computers Wireless Handsets Personal Communicators Ordering Information TEMP RANGE PIN-PACKAGE MAX1763EEE PART -40°C to +85°C 16 QSOP MAX1763EUE -40°C to +85°C 16 TSSOP-EP* *EP = Exposed pad Idle Mode is a trademark of Maxim Integrated Products. Pin Configuration 1.5µH IN 0.7V TO 5.5V LX POUT OFF ON PWM OUT 3.3V AT 1.5A MAX1763 ON OFF ONB ONA LBI OR GAIN BLOCK INPUT 16 ONB ISET 2 15 POUT REF 3 14 LX GND 4 MAX1763 FB 5 AIN ISET REF FB ONA 1 OUT CLK/SEL OR NORMAL TOP VIEW AO GND PGND LBO OR GAIN BLOCK OUTPUT 13 POUT 12 PGND OUT 6 11 LX AIN 7 10 PGND AO 8 9 CLK/SEL QSOP TSSOP-EP ________________________________________________________________ Maxim Integrated Products 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 MAX1763 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 (110µA) 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 Mode™ 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. MAX1763 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter 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 +70°C)...........667mW 16-Pin TSSOP-EP (derate 19mW/°C above +70°C) ...........1.5W Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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 = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 0.7 5.5 V 1.1 V DC-DC CONVERTER Input Voltage Range (Note 1) Minimum Startup Voltage (Note 2) ILOAD < 1mA, TA = +25°C 0.9 Temperature Coefficient of Startup Voltage ILOAD < 1mA -2 Frequency in Startup Mode VOUT = 1.5V 125 500 1000 kHz Internal Oscillator Frequency CLK/SEL = OUT 0.8 1 1.2 MHz Oscillator Maximum Duty Cycle (Note 3) 80 86 90 % External Clock Frequency Range 0.5 1.2 MHz Output Voltage VFB < 0.1V, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A 3.17 3.3 3.38 V FB Regulation Voltage Adjustable output, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A 1.215 1.245 1.270 V FB Input Current VFB = 1.35V 0.01 100 nA Load Regulation CLK/SEL = OUT, 0 < ILX < 1.1A -1.0 Output Voltage Adjust Range 2 mV/°C 2.5 V 2.15 2.30 V 0.01 50 nA 1 10 µA 200 µA Output Voltage Lockout Threshold (Note 4) Rising edge ISET Input Leakage Current VISET = 1.25V Supply Current in Shutdown V ONB = 3.6V, VONA = 0 No-Load Supply Current, LowPower Mode (Note 5) CLK/SEL = GND, AIN = OUT 110 No-Load Supply Current, LowNoise Mode CLK/SEL = OUT 2.5 Gain Block Supply Current VAIN < (VOUT - 1.4V), gain block enabled 25 2.00 % 5.5 _______________________________________________________________________________________ mA 50 µA 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter (CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS DC-DC SWITCHES POUT Leakage Current VLX = 0, VOUT = 5.5V 0.1 10 µA LX Leakage Current VLX = V ONB = VOUT = 5.5V, VONA = 0 0.1 10 µA N channel 0.075 0.13 P channel 0.13 0.25 2.0 2.5 3.4 A 10 120 240 mA 1.230 1.250 1.270 V 5 15 mV 0.2 5 mV mV Switch On-Resistance N-Channel Current Limit P-Channel Turn-Off Current CLK/SEL = GND Ω REFERENCE Reference Output Voltage IREF = 0 Reference Load Regulation -1µA < IREF < 50µA Reference Supply Rejection 2.5V < VOUT < 5V GAIN BLOCK AIN Reference Voltage IAO = 20µA AIN Input Current VAIN = 1.5V Transconductance VAO = 1V, 10µA < IAO < 100µA 910 5 938 970 ±0.01 ±30 nA 10 16 mS AO Output Low Voltage VAIN = 0.5V, IAO = 100µA 0.1 0.4 V AO Output High Leakage VAIN = 1.5V, VAO = 5.5V 0.01 1 µA 1.4 V Gain-Block Enable Threshold (VOUT - VAIN) (Note 6) Gain-Block Disable Threshold (VOUT - VAIN) (Note 6) 0.2 V LOGIC INPUTS (0.2) VOUT CLK/SEL Input Low Level 2.5V ≤ VOUT ≤ 5.5V CLK/SEL Input High Level 2.5 V ≤ VOUT ≤ 5.5V ONA and ONB Input Low Level (Note 7) 1.1 V ≤ VOUT ≤ 1.8V 0.2 1.8 V ≤ VOUT ≤ 5.5V 0.4 ONA and ONB Input High Level (Note 7) Input Leakage Current (0.8) VOUT 1.1 V ≤ VOUT ≤ 1.8V VOUT - 0.2V 1.8 V ≤ VOUT ≤ 5.5V 1.6 CLK/SEL, ONA, ONB V V V V 0.01 1 µA Minimum CLK/SEL Pulse Width 100 ns Maximum CLK/SEL Rise/Fall Time 100 ns _______________________________________________________________________________________ 3 MAX1763 ELECTRICAL CHARACTERISTICS (continued) MAX1763 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter ELECTRICAL CHARACTERISTICS (CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 8) PARAMETER CONDITIONS MIN MAX UNITS 5.5 V DC-DC CONVERTER Input Voltage Range (Note 1) Minimum Startup Voltage (Note 2) ILOAD < 1mA, TA = +25°C Frequency in Startup Mode VOUT = 1.5V 125 1.1 V kHz 0.75 1000 1.25 Internal Oscillator Frequency CLK/SEL = OUT MHz Oscillator Maximum Duty Cycle (Note 3) 80 91 % External Clock Frequency Range 0.6 1.2 MHz Output Voltage VFB < 0.1V, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A FB Regulation Voltage Adjustable output, CLK/SEL = OUT, includes load regulation for 0 < ILX < 1.1A FB Input Current VFB = 1.35V Output Voltage Adjust Range 3.17 1.215 3.38 1.270 V V 100 nA 2.5 5.5 V 2.00 2.30 V Output Voltage Lockout Threshold (Note 4) Rising edge ISET Input Leakage Current VISET = 1.25V 50 nA Supply Current in Shutdown V ONB = 3.6V, VONA = 0 10 µA No-Load Supply Current, LowPower Mode (Note 5) CLK/SEL = GND, AIN = OUT 200 µA Gain Block Supply Current VAIN < (VOUT - 1.4V), gain block enabled 50 µA POUT Leakage Current VLX = 0, VOUT = 5.5V 10 µA LX Leakage Current VLX = V ONB = VOUT = 5.5V, VONA = 0 10 µA DC-DC SWITCHES Switch On-Resistance N-channel 0.13 P-channel 0.25 N-Channel Current Limit P-Channel Turn-Off Current CLK/SEL = GND Ω 2.0 3.4 A 10 240 mA 1.220 REFERENCE Reference Output Voltage IREF = 0 1.270 V Reference Load Regulation -1µA < IREF < 50µA 15 mV Reference Supply Rejection 2.5V < VOUT < 5V 5 mV 970 mV GAIN BLOCK AIN Reference Voltage IAO = 20µA AIN Input Current VAIN = 1.5V Transconductance VAO = 1V, 10µA < IAO < 100µA AO Output Low Voltage AO Output High Leakage 4 910 ±30 nA 16 mS VAIN = 0.5V, IAO = 100µA 0.4 V VAIN = 1.5V, VAO = 5.5V 1 µA 5 _______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter (CLK/SEL = ONB = FB = PGND = GND, ISET = REF, OUT = POUT, VONA = VAIN = VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 8) PARAMETER CONDITIONS MIN MAX UNITS 1.4 V LOGIC INPUTS Gain-Block Enable Threshold (VOUT - VAIN) (Note 6) Gain-Block Disable Threshold (VOUT - VAIN) (Note 6) 0.2 V (0.2) VOUT CLK/SEL Input Low Level 2.5 V ≤ VOUT ≤ 5.5V CLK/SEL Input High Level 2.5 V ≤ VOUT ≤ 5.5V ONA and ONB Input Low Level (Note 7) 1.1 V ≤ VOUT ≤ 1.8V 0.2 1.8 V ≤ VOUT ≤ 5.5V 0.4 ONA and ONB Input High Level (Note 7) Input Leakage Current (0.8) VOUT 1.1 V ≤ VOUT ≤ 1.8V VOUT - 0.2V 1.8V ≤ VOUT ≤ 5.5V 1.6 CLK/SEL, ONA, ONB V V V V 1 µA 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 -40°C are guaranteed by design and not production tested. _______________________________________________________________________________________ 5 MAX1763 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 5V) 70 80 A B EFFICIENCY (%) C 60 50 40 A: VIN = 2.4V B: VIN = 1.2V C: VIN = 0.9V = NORMAL MODE = FPWM MODE 30 20 10 B 70 C 60 50 40 A: VIN = 3.6V B: VIN = 2.4V C: VIN = 1.2V = NORMAL MODE = FPWM MODE 30 20 10 0 3.0 2.5 0.01 0.1 1 10 VOUT = 3.3V 2.0 1.5 VOUT = 5V 1.0 0.5 0 0 0.001 0.01 0.1 1 10 0.8 1.6 2.4 3.2 OUTPUT CURRENT (A) OUTPUT CURRENT (A) INPUT VOLTAGE (V) NO-LOAD INPUT vs. INPUT VOLTAGE SHUTDOWN CURRENT vs. INPUT VOLTAGE INTERNAL OSCILLATOR FREQUENCY vs. TEMPERATURE 0.001 4.0 MAX1763 toc06 1.20 1.15 1.10 FREQUENCY (MHz) 0.01 10 MAX1763 toc05 = INPUT VOLTAGE INCREASING = INPUT VOLTAGE DECREASING SHUTDOWN CURRENT (µA) 0.1 MAX1763 toc04 0.001 INPUT CURRENT (A) A MAX1763 toc03 80 90 MAX1763 toc02 90 EFFICIENCY (%) 100 MAX1763 toc01 100 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE OUTPUT CURRENT (A) EFFICIENCY vs. OUTPUT CURRENT (VOUT = 3.3V) 1 VIN = 3.6V, VOUT = 5V 1.05 1.00 VIN = 2.4V, VOUT = 3.3V 0.95 0.90 0.85 0.80 0.1 0 1 3 2 4 0 5 1 3.1 2.6 2.1 1.6 -15 10 35 0.1 1 10 85 PEAK INDUCTOR CURRENT vs. VISET HEAVY-LOAD SWITCHING WAVEFORMS 2.5 A 2.0 B 1.5 1.0 C 0 60 TEMPERATURE (°C) 0 0.01 OUTPUT CURRENT (A) 6 -40 0.5 1.1 0.6 0.001 6 MAX1763 toc08 3.6 5 3.0 PEAK INDUCTOR CURRENT (A) MAX1763 toc07 4.1 4 INPUT VOLTAGE (V) INPUT VOLTAGE (V) STARTUP VOLTAGE vs. OUTPUT CURRENT 3 2 MAX1763 toc09 0.0001 STARTUP VOLTAGE (V) MAX1763 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter 0.2 0.4 0.6 0.8 ISET VOLTAGE (V) 1.0 1.2 1.4 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 _______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter LIGHT-LOAD SWITCHING WAVEFORMS LINE-TRANSIENT RESPONSE MAX1763 toc12 MAX1763 toc11 MAX1763 toc10 LOAD-TRANSIENT RESPONSE A A A B B C 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 40µs/div VIN = 2.4V TO 1.4V, IOUT = 70mA A: VIN, 1V/div B: VOUT, 5mV/div, AC-COUPLED 100µs/div VIN = 2.4V, VOUT = 3.3V, IOUT = 0.2A TO 1.35A A: IOUT, 0.5A/div B: VOUT, 100mV/div, AC-COUPLED MAX1763 toc13 ONA 5V/div VOUT 2V/div VOUT 2V/div IIN 1A/div ONA 5V/div IL = 10mA 2ms/div VIN = 1.2V, VOUT = 3.3V, RLOAD = 3kΩ 100µs/div STARTUP WAVEFORMS USING SOFT-START NOISE SPECTRUM MAX1763 toc15 8 ONA 5V/div 2ms/div VIN = 1.2V, VOUT = 3.3V, RSS = 510kΩ, CSS = 0.1µF, RLOAD = 3kΩ VIN = 2.4V VOUT = 3.3V 6 NOISE (mVRMS) IIN 1A/div MAX1763 toc16 IIN 0.5A/div VOUT 2V/div MAX1763 toc14 STARTUP WAVEFORMS NO SOFT-START POWER-ON DELAY 4 2 0 0.01 0.1 1 10 FREQUENCY (MHz) _______________________________________________________________________________________ 7 MAX1763 Typical Operating Characteristics (continued) (Circuit of Figure 2, VIN = +3.6V, VOUT = +5V, TA = +25°C, unless otherwise noted.) 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763 Pin Description PIN NAME FUNCTION 1 ONA On Control Input. When ONA = high or ONB = low, the IC turns on. Connect ONA to OUT for normal operation (Table 3). 2 ISET 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 (100kΩ typ) discharges this pin to GND. 3 REF 1.250V Voltage Reference Bypass Pin. Connect a 0.22µF ceramic bypass capacitor to GND. Up to 50µA of external REF load current is allowed. 4 GND Ground. Connect to PGND with short trace. 5 FB 6 OUT IC Power, Supplied from the Output. Bypass to GND with a 1.0µF ceramic capacitor, and connect to POUT with a series 4.7Ω resistor (Figure 2). 7 AIN 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. 8 AO 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. 9 CLK/SEL 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. 10, 12 PGND Source of N-Channel Power MOSFET Switch. Connect both PGND pins together close to the device. 11, 14 LX 13, 15 POUT Power Output. P-channel synchronous rectifier source. 16 ONB Off Control Input. When ONB = high and ONA = low, the IC is off. Connect ONB to GND for normal operation (Table 3). 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). Inductor Connection. Connect the LX pins together close to the device. 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 _______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter MAX1763 UNDERVOLTAGE LOCKOUT OUT IC POWER POUT CONTROLLER 2.15V EN STARTUP OSCILLATOR D Q P Q LX ONA ON ONB REF 1.25V RDY EN REFERENCE OSC EN REF GND CLK/SEL N Q 1MHz OSCILLATOR MODE DUAL MODE/ FB FB FB PGND ISET ISET AIN AO MAX1763 GAIN BLOCK N 0.938V Figure 1. Functional Diagram Table 1. Typical Available Output Current NUMBER OF CELLS 1 NiCd/NiMH INPUT VOLTAGE (V) OUTPUT VOLTAGE (V) OUTPUT CURRENT (mA) 1.2 3.3 675 2.4 3.3 1500 2.4 5.0 950 1 Li+ 2.7 (min) 3.3 1300 1 Li+ 2.7 (min) 5.0 1100 VIN 0.7V TO 5.5V MBR0520L CLK/SEL 3.6 5.0 ONA POUT ONB OUT AIN ISET PGND C2 1.0µF AO REF C3 0.22µF OUT 3.3V C4 2 x 100µF R5 4.7Ω MAX1763 1600 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 1µA. 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.) LX D1 2 NiCd/NiMH 3 NiCd/NiMH C1 47µF L1 1.5µH FB GND 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 _______________________________________________________________________________________ 9 MAX1763 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter Table 2. Selecting the Operating Mode CLK/SEL MODE FEATURES 0 Normal operation High efficiency at all loads. Fixed frequency at all but light loads. 1 Forced PWM Low noise, fixed frequency at all loads. External clock 500kHz to 1.2MHz Synchronized PWM Low noise, fixed frequency at all loads. 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. 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). 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. 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 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. Synchronous Rectifier The MAX1763 features an internal 130mΩ 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. 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. 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. Reference The MAX1763 has an internal 1.250V reference. Connect a 0.22µF ceramic bypass capacitor to GND ______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter ONA 0 ONB 0 MAX1763 On 0 1 Off 1 0 On 1 1 On RG 20k VIN 2.5V 1.5µH AO CLK/SEL LX 3.3V MBRO520L TO VIN OR VOUT ONB POUT MAX1763 AIN POWER-OK OUTPUT AO POUT R3 165k ONA C4 220µF R5 4.7Ω MAX1763 R6 150k R3 COUT 47µF C1 47µF OUT C2 1µF AIN R4 R4 100k Figure 3. Using the Gain Block as a Power-OK Comparator ISET REF C3 0.22µF PGND FB GND VIN 1.8V TO 5.5V CLK/SEL ONA ONB 0.22µF R5 4.7Ω C4 220µF RG 20k OUT C2 1.0µF ISET AO REF FB PGND LINEARREGULATED OUTPUT COUT 47µF POUT AIN R4 P LX MAX1763 R3 BOOST OUTPUT C1 47µF L1 1.5µH GND R1 R2 30k SIGNAL GROUND POWER GROUND 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 50µA 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 Figure 5. Powering a Gain-Block Linear Regulator from the Input Voltage 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 270kΩ 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) = 270mΩ). 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 ______________________________________________________________________________________ 11 MAX1763 Table 3. On/Off Logic Control MAX1763 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. OUT FB R2 R1 = R2 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 30kΩ or less, then calculate R1 using: R1 = R2((VOUT / VFB ) - 1) where VFB, the boost-regulator feedback set point, is 1.245V. 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 (>300kΩ) and a capacitor from ISET to GND. In shutdown, ISET is discharged to GND through an internal 100kΩ 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). 12 ( VV - 1), V OUT FB FB = 1.245V, R2 ≤ 30k Figure 6. Connecting Resistors for External Feedback REF ___________________Design Procedure Setting the Output Voltage R1 MAX1763 0.22µF MAX1763 RSS ISET CSS ILIM = 2.5A tSS = RSS CSS Figure 7. Soft-Start with Maximum Switch Limit Current REF 0.22µF MAX1763 RSS1 ISET RSS2 CSS ILIM = 2.5A (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 ______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter INDUCTORS CAPACITORS Coilcraft LPT3305 Motorola MBR0520L Kemet T510 series Sanyo POSCAP series Sumida Panasonic SP/CB Table 5. Component Suppliers DIODES AVX TPS series Nihon EP10QY03 resistance of the package from +115°C/W for QSOP to +53°C/W for the TSSOP-EP. At an ambient temperature of +70°C, 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. MAX1763 Table 4. Component Selection Guide SUPPLIER PHONE AVX USA: 843-448-9411 Coilcraft USA: 847-639-6400 Kemet USA: 810-287-2536 Motorola USA: 408-629-4789 Japan: 81-45-474-7030 Sumida USA: 847-956-0666 Japan: 011-81-3-3667-3302 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 External Diode 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 220µF, low equivalent-series-resistance (ESR) (less than 100mΩ) capacitor is recommended for most applications. Alternatively, two 100µF 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 47µF low-ESR input filter capacitor. With higher impedance batteries, such as alkaline and Li+, a higher value input capacitor may improve efficiency. 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 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 Inductor Selection The MAX1763’s high switching frequency allows the use of a small 1.5µH 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. ______________________________________________________________________________________ 13 MAX1763 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter 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 0.22µF. Also, bypass OUT to GND with a 1µF ceramic capacitor, and connect OUT to POUT with a 4.7Ω 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. 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. 14 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. Chip Information TRANSISTOR COUNT: 1530 SUBSTRATE CONNECTED TO GND ______________________________________________________________________________________ 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter QSOP.EPS Note: The MAX1763EEE is a 16-pin QSOP and does not have a heat slug. Use the MAX1763EUE for higher power dissipation. ______________________________________________________________________________________ 15 MAX1763 Package Information 1.5A, Low-Noise, 1MHz, Step-Up DC-DC Converter TSSOP, 4.0,EXP PADS.EPS MAX1763 Package Information (continued) 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 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.