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| 19-1217; Rev 0; 4/97 Regulated 3.3V Charge Pump _______________General Description The MAX679 step-up, regulated charge pump generates a 3.3V 4% output voltage from a 1.8V to 3.6V input voltage (two alkaline, NiCd, or NiMH; or one Lithium-Ion battery). Output current is 20mA (min) from a 2.0V input. Only three external capacitors are needed to build a complete DC-DC converter. The MAX679's switching frequency is pin selectable at 330kHz or 1MHz to allow trade-offs between lowest supply current and smallest-size capacitors. The logic shutdown function reduces the supply current to 5A (max) and disconnects the load from the input. Special soft-start circuitry prevents excessive current from being drawn from the battery during start-up. This DCDC converter requires no inductors and has low EMI. It is available in the ultra-small MAX package, which is only 1.11mm high and half the area of an 8-pin SO. ____________________________Features o Regulated 3.3V 4% Output o Ultra-Small: 1.1mm-High, 8-Pin MAX Package o No Inductors Required o Up to 1MHz Operation (small external components) o Fits into 0.05 in.2 o Up to 85% Efficiency o 1.8V to 3.6V Input Voltage Range o 50A Quiescent Supply Current o 1A Shutdown Current MAX679 ________________________Applications Battery-Powered Applications Miniature Equipment Backup-Battery Boost Converters Translators Two-Way Pagers ______________Ordering Information PART MAX679C/D MAX679EUA TEMP. RANGE 0C to +70C -40C to +85C PIN-PACKAGE Dice* 8 MAX *Dice are tested at TA = +25C only. __________Typical Operating Circuit INPUT 2V to 3.6V IN CIN OUT COUT __________________Pin Configuration OUTPUT 3.3V, 20mA TOP VIEW MAX679 FSET SHDN OFF/ON PGND GND C1C1+ FSET 1 SHDN 2 8 7 OUT C1+ C1PGND MAX679 IN 3 C1 GND 4 5 6 MAX ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 Regulated 3.3V Charge Pump MAX679 ABSOLUTE MAXIMUM RATINGS IN, OUT, SHDN, FSET to GND....................................-0.3V to 6V PGND to GND.....................................................................0.3V C1- to GND ..................................................-0.3V to (VIN + 0.3V) C1+ to GND..............................................-0.3V to (VOUT + 0.3V) OUT Short to GND ..............................................................10sec Continuous Power Dissipation (TA = +70C) MAX (derate 4.1mW/C above +70C) .......................330mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = V S HDN = VFSET = 2V, CIN = 4.7F, C1 = 0.33F, COUT = 10F, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1) PARAMETER Input Voltage Input Undervoltage Lockout Voltage Output Voltage Output Current No-Load Supply Current 2V < VIN < 3.3V, 0mA < IOUT < 20mA VIN = 1.8V, VOUT > 3.17V VIN = 2.5V, FSET = IN or GND TA = 0C to +85C TA = -40C to +85C CONDITIONS MIN 1.8 0.8 3.17 3.15 20 50 15 1 0.5 x VIN 0.7 x VIN 0.5 x VIN 0.1 260 700 330 1000 100 80 1 450 kHz FSET = IN Output Short-Circuit Current Efficiency OUT = GND, VIN = 3.3V VIN = 2V, IOUT = 10mA 1300 200 mA % 80 25 5 0.3 x VIN 3.3 TYP MAX 3.6 1.6 3.43 V 3.45 mA A A A V V A UNITS V V Leakage Current into OUT in Shutdown VOUT = 3.6V, SHDN = GND Supply Current in Shutdown FSET, SHDN Input Voltage Low FSET, SHDN Input Voltage High FSET, SHDN Input Leakage Current Switching Frequency VIN = 3.3V VIN = 1.8V VIN = 3.6V FSET, SHDN = GND or VIN FSET = GND Note 1: Specifications to -40C are guaranteed by design, not production tested. 2 _______________________________________________________________________________________ Regulated 3.3V Charge Pump __________________________________________Typical Operating Characteristics (Typical Operating Circuit with: VIN = V S HDN = 2V, CIN = 4.7F, C1 = 0.33F, COUT = 10F, tested in-circuit, TA = +25C, unless otherwise noted.) EFFICIENCY vs. OUTPUT CURRENT MAX679 TOC01a MAX679 EFFICIENCY vs. OUTPUT CURRENT MAX679 TOC01b OUTPUT VOLTAGE vs. OUTPUT CURRENT FSET = GND (330kHz) 3.5 3.4 OUTPUT VOLTAGE (V) 3.3 3.2 3.1 3.0 2.9 VIN = 1.8V DASHED LINES INDICATE OUTPUT OUT OF REGULATION 0 10 20 30 40 50 60 70 80 VIN = 2.0V VIN = 2.4V VIN = 3.5V VIN = 3.0V MAX679 TOC02a 100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 0.01 0.1 1 10 FSET = IN (1MHz) VIN = 3.0V VIN = 3.5V VIN = 2.0V VIN = 1.8V 100 90 80 70 EFFICIENCY (%) 60 50 40 30 20 10 0 FSET = GND (330kHz) VIN = 3.5V VIN = 2.0V VIN = 2.4V VIN = 3.0V VIN = 1.8V 3.6 VIN = 2.4V 2.8 0.01 0.1 1 10 100 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 100 OUTPUT CURRENT (mA) OUTPUT VOLTAGE vs. OUTPUT CURRENT MAX679 TOC02b SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX679 TOC05 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE VIN = 2.4V SHUTDOWN SUPPLY CURRENT (nA) 500 400 300 200 100 0 MAX679 TOC06 3.4 FSET = IN (1MHz) 3.3 OUTPUT VOLTAGE (V) VIN = 3.0V 3.2 VIN = 2.4V 3.1 VIN = 1.8V VIN = 2.0V VIN = 3.5V 100 SHDN = IN SUPPLY CURRENT (A) 600 10 1 SHDN = GND 3.0 DASHED LINES INDICATE OUTPUT OUT OF REGULATION 2.9 0 10 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT (mA) 0.1 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 3.6 SUPPLY VOLTAGE (V) -40 -15 10 35 60 85 TEMPERATURE (C) PUMP FREQUENCY vs. TEMPERATURE MAX679 TOC08a PUMP FREQUENCY vs. TEMPERATURE MAX679 TOC08b OUTPUT RIPPLE (2mA LOAD) FSET = GND (330kHz) MAX679 TOC09 360 350 PUMP FREQUENCY (kHz) 340 330 320 310 300 -40 -15 10 35 60 FSET = GND (330kHz) VIN = 2.5V 1100 1080 1060 PUMP FREQUENCY (kHz) 1040 1020 1000 980 960 940 920 900 FSET = IN (1MHz) VIN = 2.5V VOUT 50mV/div AC COUPLED 85 -40 -15 10 35 60 85 100s/div TEMPERATURE (C) TEMPERATURE (C) _______________________________________________________________________________________ 3 Regulated 3.3V Charge Pump MAX679 ____________________________Typical Operating Characteristics (continued) (Typical Operating Circuit with: VIN = V S HDN = 2V, CIN = 4.7F, C1 = 0.33F, COUT = 10F, tested in-circuit, TA = +25C, unless otherwise noted.) LOAD-TRANSIENT RESPONSE (1mA TO 10mA LOAD, VIN = 3V) LOAD-TRANSIENT RESPONSE (1mA TO 10mA LOAD, VIN = 2V) OUTPUT RIPPLE (2mA LOAD) MAX679 TOC10 MAX679 TOC11 MAX679 TOC12 FSET = IN (1MHz) VOUT 10mV/div AC COUPLED VOUT 50mV/div AC COUPLED IOUT 5mA/div VIN = 3V FSET = IN (1MHz) 100s/div 100s/div VIN = 2V FSET = IN (1MHz) 50s/div IOUT 5mA/div VOUT 10mV/div AC COUPLED ______________________________________________________________Pin Description PIN 1 2 3 4 5 6 7 8 NAME FSET SHDN IN GND PGND C1C1+ OUT FUNCTION Set Charge-Pump Frequency Input. FSET = GND selects 330kHz and FSET = IN selects 1MHz. Do not leave FSET unconnected. Shutdown Input. The device shuts down, the output disconnects from the input, and the supply current decreases to 1A when SHDN is a logic low. Connect SHDN to IN for normal operation. Supply Input. Connect to an input supply in the 1.8V to 3.6V range. Bypass IN to GND with a (COUT / 2)F capacitor. Ground. Analog ground for internal reference and control circuitry. Power Ground. Charge-pump current flows through this pin. Negative Terminal of the Charge-Pump Capacitor Positive Terminal of the Charge-Pump Capacitor 3.3V Power Output. Bypass OUT to GND with an output filter capacitor (see the Design Procedure section). _______________Detailed Description The MAX679 regulated charge pump has a 50% dutycycle clock. In phase one (charge phase), the chargetransfer capacitor (C1) charges to the input voltage, and output current is delivered by the output filter capacitor (COUT). In phase two (transfer phase), C1 is placed in series with the input and connects to the output, transferring its charge to COUT. If the clock were to run continuously, this process would eventually generate an output voltage equal to two times the input voltage (hence the name "doubler"). 4 The charge pump regulates by gating the oscillator on and off as needed to maintain output regulation. This method has low quiescent current, but to achieve acceptable output ripple, C1 must be significantly lower in value than COUT. Start-Up Sequence The MAX679 soft-start circuitry prevents excessive current from being drawn from the battery at start-up or when the output is shorted. This is done by limiting the charge pump to 1/10 the normal current until either the output is in regulation or the first 4096 charge-pump _______________________________________________________________________________________ Regulated 3.3V Charge Pump MAX679 IN OUT CHIP SUPPLY P6 P5 SW T P4 P3 C1+ MAX679 C P2 T SHDN PULSER P1 SW C OSCILLATOR + CONTROL LOGIC T SC CLOCK RESET FSET 212 COUNTER SC 10% OF N1 PGND C N1 C1 C1- OUT EAOUT (1 = OUTPUT OVER REGULATION POINT) 1.25V REF GND SW = T = C = SC = SWITCH CONNECTS OUT TO IN DURING START-UP TRANSFER PHASE OF PUMP CHARGE PHASE OF PUMP (FULL STRENGTH) CHARGE PHASE OF PUMP (REDUCED STRENGTH) Figure 1. Block Diagram _______________________________________________________________________________________ 5 Regulated 3.3V Charge Pump MAX679 cycles (about 4ms) have elapsed. The start-up sequence begins at power-up, when exiting shutdown, or when recovering from a short circuit. If VIN is less than the 1.6V UVLO threshold, the device remains shut down and ignores a high SHDN input. Table 1. External Component Selection VIN (V) 2 2 2 2 3 3 3 3 C1 (F) 0.33 0.33 0.1 0.1 0.33 0.33 0.1 0.1 COUT (F) 10 10 3.3 3.3 10 10 3.3 3.3 FSET (Hz) 1M 330k 1M 330k 1M 330k 1M 330k Vp-p (mV) 7 14 16 22 27 56 72 89 __________________Design Procedure Optimize the charge-pump circuit for size, quiescent current, and output ripple by properly selecting the operating frequency and capacitors C IN , C1, and COUT. For lowest output ripple, select 1MHz operation (FSET = IN). In addition, increasing COUT relative to C1 will further reduce ripple. For highest efficiency, select 330kHz operation (FSET = GND) and select the largest practical values for COUT and C1 while maintaining a 30-to-1 ratio. See Table 1 for some suggested values and the resulting output ripple. Note that the capacitors must have low ESR (<20m) to maintain low ripple. Currently, only ceramic capacitors can provide such low ESR; therefore, the output filter capacitors should be a combination of a 1F ceramic capacitor and a 10F tantalum capacitor. PC Board Layout Place C1, C OUT , and C IN close to the IC. Connect PGND and GND with a short trace. Efficiency Charge-pump efficiency is best at low frequency (330kHz). The theoretical maximum efficiency is given in the following equation: Theoretical maximum efficiency = VOUT / (2 x VIN) Gate-charge losses amount to approximately 1mA from the output at full switching frequency (about 5% to 7% loss). Smallest Size Set the frequency to 1MHz by connecting FSET to IN. Table 1 shows typical external component values. Table 2. Manufacturers of Low-ESR Capacitors PRODUCTION METHOD Surface-Mount Tantalum Capacitors Surface-Mount Ceramic Capacitors MANUFACTURER AVX Matsuo Sprague AVX Matsuo CAPACITORS TPS series 267 series 593D, 595D series X7R X7R PHONE (803) 946-0690 (714) 969-2491 (603) 224-1961 (803) 946-0690 (714) 969-2491 FAX (803) 626-3123 (714) 960-6492 (603) 224-1430 (803) 626-3123 (714) 960-6492 ___________________Chip Information TRANSISTOR COUNT: 819 SUBSTRATE CONNECTED TO GND 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. 6 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1997 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. |
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