19-1336; Rev 2; 11/98 NUAL KIT MA ATION EET H S A EVALU T WS DA FOLLO 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter ____________________________Features The MAX1703 is a high-efficiency, low-noise, step-up DC-DC converter intended for use in battery-powered wireless applications. It uses a synchronous-rectified pulse-width-modulation (PWM) boost topology to generate a 2.5V to 5.5V output from battery inputs, such as one to three NiCd/NiMH cells or one Li-Ion cell. The device includes a 2A, 75mΩ, N-channel MOSFET switch and a 140mΩ, P-channel synchronous rectifier. With its internal synchronous rectifier, the MAX1703 delivers up to 5% better efficiency than similar nonsynchronous converters. It also features a pulse-frequencymodulation (PFM) low-power mode to improve efficiency at light loads, and a 1µA shutdown mode. The MAX1703 comes in a 16-pin narrow SO package and includes an uncommitted comparator that generates a power-good or low-battery-warning output. It also contains a linear gain block that can be used to build a linear regulator. ♦ Up to 95% Efficiency ♦ Up to 1.5A Output ♦ Fixed 5V or Adjustable Step-Up Output (2.5V to 5.5V) ♦ 0.7V to 5.5V Input Range For lower-power outputs and a smaller package, refer to the MAX1700/MAX1701. For dual outputs (step-up plus linear regulator), refer to the MAX1705/MAX1706. For an on-board analog-to-digital converter, refer to the MAX848/MAX849. The MAX1703 evaluation kit is available to speed designs. ♦ Low-Power Mode (300µW) ♦ Low-Noise, Constant-Frequency Mode (300kHz) ♦ Synchronizable Switching Frequency (200kHz to 400kHz) ♦ 1µA Logic-Controlled Shutdown ♦ Power-Good Comparator ♦ Uncommitted Gain Block Ordering Information PART MAX1703ESE TEMP. RANGE PIN-PACKAGE -40°C to +85°C 16 Narrow SO ________________________Applications Digital Cordless Phones Personal Communicators PCS Phones Palmtop Computers Wireless Handsets Hand-Held Instruments Two-Way Pagers Typical Operating Circuit INPUT 0.7V TO 5.5V OUTPUT 5V OR ADJ UP TO 1.5A MAX1703 LXP, LXN OFF ON PWM OR ON POUT OUT 4 OUT GAIN-BLOCK INPUT REF FB 16 ON 15 POUT 14 LXP POK AO MAX1703 POWER-GOOD OUTPUT GAIN-BLOCK OUTPUT 13 POUT 12 PGND GND 5 POKIN AIN REF 1 POKIN 3 PFM POWER-GOOD INPUT TOP VIEW FB 2 CLK/ SEL SYNC Pin Configuration AIN 6 11 LXN AO 7 10 PGND 9 POK 8 CLK/SEL GND PGND Narrow SO ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX1703 ________________General Description MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter ABSOLUTE MAXIMUM RATINGS OUT, ON, AO, POK to GND .....................................-0.3V to +6V PGND to GND.....................................................................±0.3V LXP, LXN to PGND .................................-0.3V to (VPOUT + 0.3V) POUT, CLK/SEL, AIN, REF, FB, POKIN to GND.......................................-0.3V to (VOUT + 0.3V) Continuous Power Dissipation (TA = +70°C) Narrow SO (derate 8.70mW/°C above +70°C) .............696mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +160°C Lead Temperature (soldering, 10sec) .............................+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 = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS DC-DC CONVERTER Input Supply Range (Note 2) 0.7 5.5 V Minimum Start-Up Voltage ILOAD < 1mA, TA = +25°C (Note 3) 0.9 1.1 V Frequency in Start-Up Mode VOUT = 1.5V 40 140 300 kHz Output Voltage (Note 4) VFB < 0.1V, CLK/SEL = OUT, 0 ≤ ILX ≤ 1.1A, VBATT = 3.7V 4.87 5.05 5.20 V FB Regulation Voltage Adjustable output, CLK/SEL = OUT, 0 ≤ ILX ≤ 1.1A, VBATT = 2.2V, VOUT = 3.3V 1.21 1.24 1.255 V FB Input Current VFB = 1.25V 20 nA 5.5 V 0.1 Output Voltage Adjust Range 2.5 Output Voltage Lockout Threshold (Note 5) 2.0 2.15 2.3 Load Regulation (Note 6) CLK/SEL = OUT, no load to full load -1.6 V Supply Current in Shutdown ON = OUT 0.1 20 µA Supply Current in Low-Power Mode CLK/SEL = GND (Note 1) 65 120 µA Supply Current in Low-Noise Mode CLK/SEL = OUT (Note 1) 150 300 µA POUT, LXP Leakage Current VLXP = 0V, VOUT = V ON = 5.5V 0.1 20 µA LXN Leakage Current V ON = VLXN = VOUT = 5.5V 0.1 20 µA Switch On-Resistance Switch On-Resistance N-channel CLK/SEL = GND 0.14 0.25 CLK/SEL = OUT 0.075 0.13 0.13 0.25 % DC-DC SWITCHES P-channel N-Channel Current Limit P-Channel Turn-Off Current Ω CLK/SEL = OUT 2200 2700 3200 mA CLK/SEL = GND 500 800 1100 mA CLK/SEL = GND 20 160 260 mA 1.250 1.275 V 20 nA POWER-GOOD COMPARATOR POKIN Trip Level Rising VPOKIN 1.225 POKIN Input Current VPOKIN = 0.7V -20 POK Low Voltage ISINK(POK) = 1mA, VOUT = 3.6V or ISINK(POK) = 20µA, VOUT = 1V 0.03 0.4 V POK High Leakage Current VOUT = VPOK = 5.5V 0.01 1 µA 2 _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter (CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 1.25 1.263 V 30 nA 10 16 mmho GAIN BLOCK AIN Reference Voltage IAO = 20µA 1.237 AIN Input Current VAIN = 1.5V -30 Transconductance 10µA < IAO < 100µA 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 5 REFERENCE Reference Output Voltage IREF = 0µA 1.250 1.263 V REF Load Regulation -1µA < IREF < 50µA 1.237 5 15 mV REF Supply Rejection 2.5V < VOUT < 5.5V 0.2 5 mV LOGIC INPUTS Input Low Voltage Input High Voltage ON, 1.2V < VOUT < 5.5V (Note 7) 0.2VOUT CLK/SEL, VOUT = 2.5V 0.2VOUT ON, 1.2V < VOUT < 5.5V 0.8VOUT CLK/SEL, VOUT = 5.5V 0.8VOUT Logic Input Current ON, CLK/SEL Internal Oscillator Frequency CLK/SEL = OUT, VFB = 0.5V Oscillator Maximum Duty Cycle CLK/SEL = OUT, VFB = 0.5V External Clock Frequency Range V V V -1 0.01 1 µA 260 300 340 kHz 80 86 200 90 % 400 kHz Minimum CLK/SEL Pulse Width 200 ns Maximum CLK/SEL Rise/Fall Time 100 ns ELECTRICAL CHARACTERISTICS (CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 8) PARAMETER CONDITIONS MIN TYP MAX UNITS DC-DC CONVERTER Output Voltage (Note 4) VFB < 0.1V, CLK/SEL = OUT, 0 ≤ ILX ≤ 1.1A, VBATT = 3.7V 4.87 5.20 V FB Regulation Voltage Adjustable output, CLK/SEL = OUT, 0 ≤ ILX ≤ 1.1A, VOUT = 3.3V, VBATT = 2.2V 1.20 1.27 V Output Voltage Lockout Threshold (Note 5) 2.0 2.3 V Supply Current in Shutdown ON = OUT 20 µA Supply Current in Low-Power Mode CLK/SEL = GND (Note 1) 120 µA Supply Current in Low-Noise Mode CLK/SEL = OUT (Note 1) 300 µA _______________________________________________________________________________________ 3 MAX1703 ELECTRICAL CHARACTERISTICS (continued) MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (CLK/SEL = AIN = ON = POKIN = FB = PGND = GND, OUT = POUT, LXP = LXN, VOUT = 5.3V (Note 1), TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 8) PARAMETER CONDITIONS MIN TYP MAX UNITS DC-DC SWITCHES Switch On-Resistance N-channel CLK/SEL = GND 0.25 CLK/SEL = OUT 0.13 P-channel Ω 0.25 CLK/SEL = OUT 2200 3600 mA CLK/SEL = GND 500 1100 mA Rising VPOKIN 1.225 1.275 V AIN Reference Voltage IAO = 20µA 1.23 1.27 V Transconductance 10µA < IAO < 100µA 5 16 mmho IREF = 0µA 1.23 1.27 V Internal Oscillator Frequency CLK/SEL = OUT, VFB = 0.5V 260 340 kHz Oscillator Maximum Duty Cycle CLK/SEL = OUT, VFB = 0.5V 80 92 % N-Channel Current Limit POWER-GOOD COMPARATOR POKIN Trip Level GAIN BLOCK REFERENCE Reference Output Voltage LOGIC INPUTS Note 1: Supply current from the 5.05V output is measured between the 5.05V 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 = 5.3V to keep the internal switch open when measuring the device operating current. Note 2: Minimum operating voltage. Since the regulator is bootstrapped to the output, once started it will operate down to a 0.7V input. Note 3: Start-up is tested with the circuit of Figure 2. Note 4: In low-power mode (CLK/SEL = GND) the output voltage regulates 1% higher than low-noise mode (CLK/SEL = OUT or synchronized). Note 5: The regulator is in start-up mode until this voltage is reached. Do not apply full-load current below this voltage. Note 6: Load regulation is measured from no-load to full load, where full load is determined by the N-channel switch current limit. Note 7: The ON input has a total hysteresis of approximately 0.15 x VOUT. Note 8: Specifications to -40°C are guaranteed by design and not production tested. 4 _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter 70 90 VIN = 1.2V 60 PFM PWM 50 VIN = 0.9V 70 60 LOW-POWER MODE 100 1000 10,000 0.1 1 TA = +25°C TA = -40°C 10 100 1000 10,000 0 1 2 3 4 LOAD CURRENT (mA) INPUT VOLTAGE (V) SHUTDOWN SUPPLY CURRENT vs. INPUT VOLTAGE START-UP VOLTAGE vs. LOAD CURRENT REFERENCE VOLTAGE vs. TEMPERATURE 1.0 TA = +25°C, TA = -40°C 1.4 1.2 1.0 0.6 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0.1 1 10 100 1000 -40 -20 0 LOAD CURRENT (mA) 20 40 60 TEMPERATURE (°C) REFERENCE VOLTAGE vs. REFERENCE CURRENT NOISE SPECTRUM 1.2520 VIN = 3.6V VOUT = 5V LOW-POWER MODE 9 VOUT = 5V VIN = 3.6V ILOAD = 500mA 8 7 1.2500 NOISE (mVRMS) REFERENCE VOLTAGE (V) 100 1.2490 1.2450 0.01 INPUT VOLTAGE (V) 1.2510 80 1.2510 1.2470 0.8 0 1.2530 1.2490 1.2480 MAX1703-14 0.5 1.6 6 MAX1703-06 1.8 REFERENCE VOLTAGE (V) TA = +85°C 1.5 VOUT = 5V PWM MODE 5 1.2550 MAX1703-05 2.0 MAX1703-04 INCLUDES ALL EXTERNAL COMPONENT LEAKAGES. CAPACITOR LEAKAGE DOMINATES AT TA = +85°C MAX1703-07 2.0 10 1 LOAD CURRENT (mA) START-UP VOLTAGE (V) 2.5 1 TA = +85°C 2 0 40 0.1 3 PFM PWM 50 40 SHUTDOWN CURRENT (µA) VIN = 1.2V 80 4 BATTERY CURRENT (mA) VIN = 2.4V 80 VIN = 2.4V EFFICIENCY (%) EFFICIENCY (%) 90 100 MAX1703-02 VIN = 3.6V MAX1703-01 100 NO-LOAD BATTERY CURRENT vs. INPUT VOLTAGE EFFICIENCY vs. LOAD CURRENT (VOUT = 3.3V) MAX1703-03 EFFICIENCY vs. LOAD CURRENT (VOUT = 5V) 6 5 4 3 2 1.2470 1 1.2460 -1 0 0 10 20 30 40 50 60 70 REFERENCE CURRENT (µA) 80 90 100 1k 10k 100k 1M 10M FREQUENCY (Hz) _______________________________________________________________________________________ 5 MAX1703 __________________________________________Typical Operating Characteristics (VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.) _________________________________Typical Operating Characteristics (continued) (VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.) PEAK INDUCTOR CURRENT LIMIT vs. OUTPUT VOLTAGE FREQUENCY vs. TEMPERATURE 330 MAX1703-16 3.5 MAX1703-15 340 PWM 3.0 310 CURRENT LIMIT(A) 320 FREQUENCY (kHz) MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter VOUT = 5V 300 290 2.5 2.0 1.5 280 VOUT = 3.3V LOW POWER (PFM) 1.0 270 0.5 260 -40 -20 0 20 40 60 80 2.5 100 3.0 3.5 4.0 4.5 5.0 5.5 OUTPUT VOLTAGE (V) TEMPERATURE (°C) LINE-TRANSIENT RESPONSE HEAVY LOAD SWITCHING MAX1703-09 MAX1703-08 VOUT (50mV/div) 4V VIN 2V 0V 2ms/div 2µs/div VIN = 2.6V TO 3.6V, VOUT IS AC COUPLED ILOAD = 1.5A, C7 = 0.47µF POWER-ON DELAY (PFM MODE) LOAD-TRANSIENT RESPONSE MAX1703-11 MAX1703-10 VON VOUT (50mV/div) VOUT (2V/div) 1.0A IIN (0.2A/div) 0.5A 0A 2ms/div VOUT IS AC COUPLED LOAD CURRENT = 0A TO 1.5A 6 1ms/div VIN = 2.6V TO 3.6V, VOUT IS AC COUPLED _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter GSM LOAD-TRANSIENT RESPONSE DECT LOAD-TRANSIENT RESPONSE MAX1703-12 MAX1703-13 VOUT (100mV/div) VOUT (100mV/div) ILOAD (0.5A/div) ILOAD (0.2A/div) 1ms/div 2ms/div VIN = 3.6V, VOUT = 5V, COUT = 470µF, PULSE WIDTH = 577µs, LOAD CURRENT = 100mA TO 1A VIN = 1.2V, VOUT = 3.3V, COUT = 470µF, PULSE WIDTH = 416µs, LOAD CURRENT = 50mA TO 400mA Pin Description PIN NAME 1 REF 2 FB 3 POKIN FUNCTION Reference Output. Bypass with a 0.22µF bypass capacitor to GND. Dual-Mode™ Feedback Input. Connect FB to ground to set a fixed output voltage of +5V. Connect a divider between the output voltage and GND to set the output voltage from 2.5V to 5.5V. Power-Good Comparator Input. Threshold is 1.250V, with 1% hysteresis on the threshold’s rising edge. 4 OUT DC-DC Converter Output. Power source for the IC. 5 GND Ground 6 AIN Gain-Block Input. When AIN is low, AO sinks current. The nominal transconductance from AIN to AO is 10mmhos. 7 AO Gain-Block Output. This open-drain output sinks current when VAIN < VREF. 8 POK Power-Good Comparator Output. This open-drain N-channel output is low when VPOKIN < 1.250V. Switch-Mode Selection and External-Clock Synchronization Input: • CLK/SEL = Low: Low-power, low-quiescent-current PFM mode. Delivers up to 10% of full load current. • CLK/SEL = High: High-power PWM mode. Full output power available. Operates in low-noise, constantfrequency mode. • CLK/SEL = External Clock: High-power PWM mode with the internal oscillator synchronized to the external CLK 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. 9 CLK/SEL 10, 12 PGND 11 LXN 13, 15 POUT 14 LXP Drain of P-Channel Synchronous Rectifier. Connect LXP to LXN. 16 ON On/Off Input. When ON is low, the IC turns on. Source of N-Channel Power MOSFET Switch Drain of N-Channel Power Switch. Connect LXP to LXN. Source of P-Channel Synchronous Rectifier MOSFET Switch. Connect an external Schottky diode from LXN and LXP to POUT. Dual Mode is a trademark of Maxim Integrated Products. _______________________________________________________________________________________ 7 MAX1703 _________________________________Typical Operating Characteristics (continued) (VIN = +3.6V, VOUT = 5V, TA = +25°C, unless otherwise noted.) MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter UNDERVOLTAGE LOCKOUT OUT IC POWER PFM/PWM CONTROLLER 2.15V EN OUT START-UP OSCILLATOR D Q Q POUT P LXP ON ON REF 1.25V RDY FB OSC EN REF GND CLK/SEL LXN EN REFERENCE 300kHz OSCILLATOR OUT DUAL MODE/ FB Q PFM/PWM N MODE PGND FB COMPARATOR POKIN POK N REF MAX1703 AIN AO GAIN BLOCK N REF Figure 1. Functional Block Diagram _______________Detailed Description The MAX1703 is a highly efficient, low-noise power supply for portable RF and data-acquisition instruments. It combines a boost switching regulator, Nchannel power MOSFET, P-channel synchronous rectifier, precision reference, shutdown control, versatile gain block, and power-good (POK) comparator (Figure 1) in a 16-pin narrow SO package. The switching DC-DC converter boosts a 1- to 3-cell input to a fixed 5V or an adjustable output between 2.5V and 5.5V. Typically the MAX1703 starts from a low, 0.9V input and remains operational down to 0.7V. 8 The MAX1703 is optimized for use in cellular phones and other applications requiring low noise during fullpower operation, as well as low quiescent current for maximum battery life in low-power mode and shutdown. It features constant-frequency (300kHz), lownoise PWM operation with up to 1.5A output capability. See Table 1 for typical outputs. A low-quiescent-current, low-power mode offers an output up to 150mA and reduces quiescent power consumption to 300µW. In shutdown mode, the quiescent current is further reduced to just 1µA. Figure 2 shows the standard application circuit for the MAX1703. _______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter Table 2. Selecting the Operating Mode INPUT VOLTAGE (V) OUTPUT VOLTAGE (V) OUTPUT CURRENT (mA) CLK/SEL MODE FEATURES NO. OF CELLS 0 Low power Low supply current 1 NiCd/NiMH 1.2 3.3 600 1 PWM Low noise, high output current 2.4 3.3 1400 2.4 5.0 950 External Clock (200kHz to 400kHz) Synchronized PWM Low noise, high output current 3.6 5.0 1600 2 NiCd/NiMH 3 NiCd/NiMH MAX1703 Table 1. Typical Available Output Current Step-Up Converter VBATT C1 100µF L1 4.7µH MBR0520L CLK/SEL LXP, LXN D1 C4 2 x 220µF POUT R5 10Ω MAX1703 ON OUT C5 0.22µF C2 0.22µF AIN R3 AO POKIN POK REF R4 C3 0.22µF FB PGND GND SIGNAL GROUND NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS. POWER GROUND Figure 2. MAX1703 in High-Power PWM Mode Additional features include synchronous rectification for high efficiency and improved battery life, and an uncommitted comparator (POK) for monitoring the regulator’s output or battery voltage. The MAX1703 also includes a gain block that can be used to build a linear regulator using an external P-channel MOSFET pass device; this gain block can also function as a second comparator. A CLK input allows frequency synchronization to reduce interference. The step-up switching DC-DC converter generates an adjustable output from 2.5V to 5.5V. The internal Nchannel MOSFET switch is turned on during 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, when the MOSFET is turned off, the voltage across the inductor reverses and forces current through the diode and synchronous rectifier to the output filter capacitor and load. As the energy stored in the inductor is depleted, the current ramps down and the output diode and synchronous rectifier turn off. Depending on the CLK/SEL pin setting, voltage across the load is regulated using either low-noise PWM or low-power operation (Table 2). Low-Noise PWM Operation When CLK/SEL is pulled high, the MAX1703 operates in a high-power, low-noise PWM mode. During PWM operation, the MAX1703 switches at a constant frequency (300kHz), and modulates the MOSFET-switch pulse width to control the power transferred per cycle and regulate the voltage across the load. In PWM mode the device can output up to 1.5A. Switching harmonics generated by fixed-frequency operation are consistent and easily filtered. See the Noise Spectrum plot in the Typical Operating Characteristics. During PWM operation, each of the internal clock’s rising edges sets a flip-flop, which turns on the N-channel MOSFET switch (Figure 3). The switch turns 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, the comparator shifts the level to which the inductor current ramps during each cycle. A second comparator enforces an inductor current limit of 2.7A (typical). _______________________________________________________________________________________ 9 MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter S POUT LOGIC HIGH D POUT Q FB P R P REF R LXP LXN Q S N ERROR COMPARATOR FB LXP LXN S Q N REF 2.7A TYP CURRENT LIMIT R PGND 800mA TYP CURRENT LIMIT OSC PGND Figure 3. Simplified PWM Controller Block Diagram Figure 4. Controller Block Diagram in Low-Power PFM Mode Synchronized PWM Operation The MAX1703 can be synchronized in PWM mode to a 200kHz to 400kHz frequency by applying an external clock to CLK/SEL. This allows the user to set the harmonics to avoid IF bands in wireless applications. The synchronous rectifier is also active during synchronized PWM operation. nal, 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 rectifier current has ramped down to 80mA. This forces operation with a discontinuous inductor current. Low-Power PFM Operation Pulling CLK/SEL low places the MAX1703 in a lowpower 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 pulse 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 150mA (max). The output voltage is typically 1% higher than in PWM mode. During PFM operation, the error comparator detects the output voltage falling out of regulation and sets a flipflop, which turns on the N-channel MOSFET switch (Figure 4). When the inductor current ramps to the PFM mode current limit (800mA typical) and stores a fixed amount of energy, the current-sense comparator resets a flip-flop. 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” sig10 Synchronous Rectifier The MAX1703 features an internal 140mΩ, P-channel 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 lowpower 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 80mA. Low-Voltage Start-Up Oscillator The MAX1703 uses a CMOS, low-voltage start-up oscillator for a 1.1V guaranteed minimum start-up input voltage at +25°C. On start-up, the low-voltage oscillator switches the N-channel MOSFET until the output voltage reaches 2.15V. Above this level, the normal boostconverter 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 via the OUT pin. Do not apply full load until the output exceeds 2.3V (max). ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter Reference The MAX1703 has an internal 1.250V, 1% bandgap reference. Connect a 0.22µF bypass capacitor to GND within 0.2in. (5mm) of the REF pin. REF can source up to 50µA of external load current. Power-Good (POK) Comparator The MAX1703 gain block can function as a second comparator, or can be used to build a linear regulator 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 g m of the entire gain-block stage is 10mmho. Figure 6 shows the gain block used in a linear-regulator application. 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 an NDS336P (RDS(ON) = 270mΩ) from Fairchild. This configuration allows ripple reduction at the output. If a lower RDS(ON) PFET is used, then the linear regulator output filter capacitance may need to be increased. The MAX1703 features an uncommitted POK comparator. The internal POK comparator has an open-drain output (POK) capable of sinking 1mA. When the input (POKIN) rises above the 1.25V reference, the POK open-drain output turns off. The POKIN input has 10mV of hysteresis. To provide a power-good signal, connect the POKIN input to an external resistor-divider between OUT and GND (Figure 5). Calculate the resistor values as follows: R3 = R4(VTH / VREF - 1) where VTH is the desired input voltage trip threshold. Since the input bias current into POKIN is less than 20nA, R4 can be a large value (such as 270kΩ or less) without sacrificing accuracy. Connect the resistor voltage-divider as close to the IC as possible, within 0.2in. (5mm) of POKIN. Gain Block To use the gain block as a comparator, refer to the Power-Good (POK) Comparator section. VIN VIN C1 100µF L1 4.7µH L1 4.7µH MBR0520L CLK/SEL OUTPUT LXP, LXN ON OUT AO POKIN POK R1 REF R4 GND C5 0.22µF AO R4 FB PGND 47µF POK R1 REF R6 20k LINEAR REGULATED OUTPUT C2 0.22µF AIN POKIN C3 0.22µF R5 10Ω MAX1703 R3 C2 0.22µF AIN R3 P C4 330µF POUT C5 0.22µF R5 10Ω OUT CLK/SEL C4 2 x 220µF POUT MAX1703 MBR0520L LXP, LXN D1 ON BOOST OUTPUT C1 100µF PGND R2 SIGNAL GROUND POWER GROUND FB GND R2 100k SIGNAL GROUND POWER GROUND NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS. Figure 5. Adjustable Output (PWM Mode) Figure 6. Using the Gain Block as a Linear Regulator ______________________________________________________________________________________ 11 MAX1703 Shutdown The MAX1703 shuts down to reduce quiescent current to 1µA. During shutdown (ON = VOUT), 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. MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter Table 3. Component Selection Guide PRODUCTION INDUCTORS Sumida CDR125 Surface Mount Sumida RCH654 series __________________Design Procedure 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) where VFB, the boost-regulator feedback setpoint, is 1.24V. Since the input bias current into FB is less than 20nA, R2 can have a large value (such as 270kΩ 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. DIODES Matsuo 267 series Sprague 595D series Coilcraft DO3316 Through Hole CAPACITORS Motorola MBR0520L AVX TPS series Sanyo OS-CON series Nichicon PL series 1N5817 Table 4. Component Suppliers SUPPLIER PHONE FAX AVX USA: (803) 946-0690 (800) 282-4975 (803) 626-3123 Coilcraft USA: (847) 639-6400 (847) 639-1469 Matsuo USA: (714) 969-2491 (714) 960-6492 Motorola USA: (602) 303-5454 (602) 994-6430 Sanyo USA: (619) 661-6835 Japan: 81-7-2070-6306 (619) 661-1055 81-7-2070-1174 Sumida USA: (847) 956-0666 Japan: 81-3-3607-5111 (847) 956-0702 81-3-3607-5144 Inductor Selection The MAX1703’s high switching frequency allows the use of a small surface-mount inductor. A 4.7µH inductor should have a saturation-current rating that exceeds the N-channel switch current limit. 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. See Table 3 for suggested components and Table 4 for a list of component suppliers. Connect the inductor from the battery to the LX pins as close to the IC as possible. Output Diode Use a Schottky diode such as a 1N5817, MBR0520L, or equivalent. The Schottky diode carries current during both start-up and PFM mode after the synchronous rectifier turns off. Thus, its current rating only needs to be 500mA. Connect the diode between LXN/LXP 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. 12 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. A 330µF, 100mΩ, low-ESR tantalum capacitor is recommended for a 5V output. For full output load current, one 470µF or two 220µF, 100mΩ low-ESR tantalum capacitors are recommended for a 3.3V output. The input filter capacitor (CIN) also 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 MAX1703, use a 100µF, low-ESR input filter capacitor. 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 exceed the ripple current ratings of tantalum capacitors. Avoid most aluminum-electrolytic capacitors, because their ESR is often too high. ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter CON 4.7nF __________ Applications Information Intermittent Supply/Battery Connections When boosting an input supply connected via a mechanical switch, or a battery connected via 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 MAX1703’s internal MOSFET switch control. If contact or switch bounce is anticipated in the design, use one of the following solutions: 1) Connect a capacitor (CON) from ON to VIN and a 1MΩ resistor (RON) from ON to GND, as shown in Figure 7. This resistor-capacitor network differentiates fast input edges at VIN and momentarily holds the IC off until VIN settles. The appropriate value of CON is 10-5 times the total output filter capacitance (COUT), so a COUT of 440µF results in CON = 4.7nF. 2) Use the system microcontroller to hold the MAX1703 in shutdown from the time when power is applied (or reapplied) until COUT has charged to at least the input voltage. Standard power-on-reset times 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 output voltage has settled and all of the system’s power-on-reset flags are cleared. Use in a Typical Wireless Phone Application The MAX1703 is 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 8). Low-dropout linear regulators are used for post-regulation to generate 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). See Gain Block section for information on configuring an external MOSFET as a linear regulator. RON 1M 16 ON LXP, LXN 11, 14 COUT 2 x 220µF MAX1703 OUT POUT 4 15, 13 Figure 7. Connecting CON and RON when Switch or BatteryContact Bounce is Anticipated 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 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, 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 lownoise 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. 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 and separated from them using grounded copper. Consult the MAX1703 EV kit for a full PC board example. Soft-Start To implement soft-start, set CLK/SEL low on power-up; this forces PFM operation and reduces the peak switching current to 800mA max. Once the circuit is in regulation and start-up transients have settled, CLK/SEL can be set high for full-power operation. ______________________________________________________________________________________ 13 MAX1703 Bypass Capacitors A few ceramic bypass capacitors are required for proper operation. Bypass REF with a 0.22µF capacitor to GND. Connect a 0.22µF ceramic capacitor from OUT to GND. Each of these 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. 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter MAX1703 ___________________Chip Information LX TRANSISTOR COUNT: 554 SUBSTRATE CONNECTED TO GND POUT MAX1703 LDOs MAX8865/MAX8866 PA µC RADIO Figure 8. Typical Phone Application 14 ______________________________________________________________________________________ 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter SOICN.EPS ______________________________________________________________________________________ 15 MAX1703 ________________________________________________________Package Information MAX1703 1-Cell to 3-Cell, High-Power (1.5A), Low-Noise, Step-Up DC-DC Converter NOTES 16 ______________________________________________________________________________________