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| EVALUATION KIT AVAILABLE 1 TC682 INVERTING VOLTAGE DOUBLER FEATURES s s s s s s 99.9% Voltage Conversion Efficiency 92% Power Conversion Efficiency Wide Input Voltage Range ............... +2.4V to +5.5V Only 3 External Capacitors Required 185A Supply Current Space-Saving 8-Pin SOIC and 8-Pin Plastic DIP Packages GENERAL DESCRIPTION The TC682 is a CMOS charge pump converter that provides an inverted doubled output from a single positive supply. An on-board 12kHz (typical) oscillator provides the clock and only 3 external capacitors are required for full circuit implementation. Low output source impedance (typically 140), provides output current up to 10mA. The TC682 features low quiescent current and high efficiency, making it the ideal choice for a wide variety of applications that require a negative voltage derived from a single positive supply (for example: generation of - 6V from a 3V lithium cell or - 10V generated from a +5V logic supply). The minimum external parts count and small physical size of the TC682 make it useful in many medium-current, dual voltage analog power supplies. 2 3 4 5 6 7 8 7 NC C1+ VIN GND TC682-2 8/21/96 APPLICATIONS s s s s s s s - 10V from +5V Logic Supply - 6V from a Single 3V Lithium Cell Portable Handheld Instruments Cellular Phones LCD Display Bias Generator Panel Meters Operational Amplifier Power Supplies ORDERING INFORMATION Part No. TC682COA TC682CPA TC682EOA TC682EPA TC7660EV Package 8-Pin SOIC 8-Pin Plastic DIP 8-Pin SOIC 8-Pin Plastic DIP Evaluation Kit for Charge Pump Family Temp. Range 0C to +70C 0C to +70C - 40C to +85C - 40C to +85C TYPICAL OPERATING CIRCUIT VIN +2.4V < VIN < +5.5V PIN CONFIGURATIONS C1+ C1- C2+ C2- TC682 VOUT GND VOUT = - (2 x VIN ) VOUT + COUT C1- 1 C2+ 2 C2- 3 VOUT 4 TC682COA TC682EOA VIN C1- C2+ C2- VOUT 1 2 3 4 8-Pin DIP 8 7 TC682CPA TC682EPA 6 5 NC C1+ VIN GND + C1 - + C2 - 8-Pin SOIC GND All Caps = 3.3F 6 5 8 4-21 TELCOM SEMICONDUCTOR, INC. INVERTING VOLTAGE DOUBLER TC682 ABSOLUTE MAXIMUM RATINGS* VIN .......................................................................... +5.8V VIN dV/dT ............................................................. 1V/sec VOUT ......................................................................- 11.6V VOUT Short-Circuit Duration ............................ Continuous Power Dissipation (TA 70C) Plastic DIP ........................................................... 730mW SOIC ...............................................................470mW Storage Temperature Range ................ - 65C to +150C Lead Temperature (Soldering, 10 sec) ................. +300C *This is a stress rating only and functional operation of the device at these or any other conditions above 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: Over Operating Temperature Range, VIN = +5V, test circuit Figure 1, unless otherwise indicated. Symbol VIN IIN ROUT Parameter Supply Voltage Range Supply Current VOUT Source Resistance Source Resistance Oscillator Frequency Power Efficiency Voltage Conversion Efficiency Test Conditions RL = 2k RL = , TA = 25C RL = - IL = 10mA, TA = 25C - IL = 10mA - IL = 5mA, VIN = 2.8V RL = 2k, TA = 25C VOUT, RL = Min 2.4 -- -- -- -- -- -- 90 99 Typ -- 185 -- 140 -- 170 12 92 99.9 Max 5.5 300 400 180 230 320 -- -- -- Unit V A FOSC PEFF VOUT EFF kHz % % TelCom Semiconductor reserves the right to make changes in the circuitry or specifications detailed in this manual at any time without notice. Minimums and maximums are guaranteed. All other specifications are intended as guidelines only. TelCom Semiconductor assumes no responsibility for the use of any circuits described herein and makes no representations that they are free from patent infringement. PIN DESCRIPTION Pin No. 8-Pin DIP/SOIC Symbol Description 1 2 3 4 5 6 7 8 - C1 + C2 - C2 VIN (+5V) 7 1 2 3 C1+ C1- 6 VIN + C1 - VOUT GND VIN + C1 N/C Input. Capacitor C1 negative terminal. Input. Capacitor C2 positive terminal. Input. Capacitor C2 negative terminal Output. Negative output voltage (- 2VIN) Input. Device ground. Input. Power supply voltage. Input. Capacitor C1 positive terminal No Connection TC682 + C2 - C2+ C2- V OUT GND 5 GND 4 C + OUT - RL - VOUT All Caps = 3.3F Figure 1. TC682 Test Circuit 4-22 TELCOM SEMICONDUCTOR, INC. INVERTING VOLTAGE DOUBLER 1 TC682 EFFICIENCY CONSIDERATIONS Theoretically a charge pump voltage multiplier can approach 100% efficiency under the following conditions: * The charge pump switches have virtually no offset and are extremely low on resistance. * Minimal power is consumed by the drive circuitry * The impedances of the reservoir and pump capacitors are negligible. For the TC682, efficiency is as shown below: DETAILED DESCRIPTION Phase 1 VSS charge storage - before this phase of the clock + cycle, capacitor C1 is already charged to +5V. C1 is then - - switched to ground and the charge in C1 is transferred to C2 + . Since C2 is at +5V, the voltage potential across capacitor C2 is now -10V. VIN = +5V 2 3 4 5 6 SW1 + - + C1 SW2 -5V - SW3 C2 SW4 - + VOUT C3 Voltage Efficiency = VOUT / (- 2VIN) VOUT = - 2VIN + VDROP VDROP = (IOUT) (ROUT) Power Loss = IOUT (VDROP) Figure 2. Charge Pump - Phase 1 Phase 2 VSS transfer - phase two of the clock connects the negative terminal of C2 to the negative side of reservoir capacitor C3 and the positive terminal of C2 to ground, transferring the generated - 10V to C3. Simultaneously, the positive side of capacitor C1 is switched to +5V and the negative side is connected to ground. C2 is then switched to VCC and GND and Phase 1 begins again. +5V There will be a substantial voltage difference between V- and 2 VIN if the impedances of the pump capacitors OUT C1 and C2 are high with respect to their respective output loads. Larger values of reservoir capacitor C3 will reduce output ripple. Larger values of both pump and reservoir capacitors improve the efficiency. See "Capacitor Selection" in Applications section. APPLICATIONS Negative Doubling Converter The most common application of the TC682 is as a charge pump voltage converter which provides a negative output of two times a positive input voltage (Figure 4). SW1 + - C1 SW2 + - SW3 VOUT C2 - + -10V C2 22F 3 C- 2 4 SW4 C3 C1 22F 1 - C1 C1+ 7 2 C+ 2 TC682 VIN GND Figure 3. Charge Pump - Phase 2 6 5 VIN GND C3 22F - VOUT 7 MAXIMUM OPERATING LIMITS The TC682 has on-chip zener diodes that clamp VIN to - approximately 5.8V, and VOUT to - 11.6V. Never exceed the maximum supply voltage or excessive current will be shunted by these diodes, potentially damaging the chip. The TC682 will operate over the entire operating temperature range with an input voltage of 2V to 5.5V. TELCOM SEMICONDUCTOR, INC. - V OUT Figure 4. Inverting Voltage Doubler 4-23 8 INVERTING VOLTAGE DOUBLER TC682 Capacitor Selection The output resistance of the TC682 is determined, in part, by the ESR of the capacitors used. An expression for ROUT is derived as shown below: ROUT = 2(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2) +2(RSW1 + RSW2 + ESRC1 + RSW3 + RSW4 + ESRC2) +1/(fPUMP x C1) +1/(fPUMP x C2) +ESRC3 Assuming all switch resistances are approximately equal... ROUT = 16RSW + 4ESRC1 + 4ESRC2 + ESRC3 +1/(fPUMP x C1) +1/(fPUMP x C2) ROUT is typically 140 at +25C with VIN = +5V and 3.3F low ESR capacitors. The fixed term (16RSW) is about 80-90. It can be seen easily that increasing or decreasing values of C1 and C2 will affect efficiency by changing ROUT. However, be careful about ESR. This term can quickly become dominant with large electrolytic capacitors. Table 1 shows ROUT for various values of C1 and C2 (assume 0.5 ESR). C1 must be rated at 6VDC or greater while C2 and C3 must be rated at 12VDC or greater. Output voltage ripple is affected by C3. Typically the larger the value of C3 the less the ripple for a given load current. The formula for P-P VRIPPLE is given below: VRIPPLE = {1/[2(fPUMP x C3)] + 2(ESRC3)} (IOUT) For a 10F (0.5 ESR) capacitor for C3, fPUMP = 10kHz and IOUT = 10mA the peak-to-peak ripple voltage at the output will be less then 60mV. In most applications (IOUT < = 10mA) a 10-20F capacitor and 1-5F pump capacitors will suffice. Table 2 shows VRIPPLE for different values of C3 (assume 1 ESR). Table 1. ROUT vs. C1, C2 C1, C2 (F) 0.05 0.10 0.47 1.00 3.30 5.00 10.00 22.00 100.00 Table 2. VRIPPLE Peak- to-Peak vs. C3 (IOUT = 10mA) C3 (F) 0.50 1.00 3.30 5.00 10.00 22.00 100.00 VRIPPLE (mV) 1020 520 172 120 70 43 25 Paralleling Devices Paralleling multiple TC682s reduces the output resistance of the converter. The effective output resistance is the output resistance of a single device divided by the number of devices. As illustrated in Figure 5, each requires separate pump capacitors C1 and C2, but all can share a single reservoir capacitor. -5V Regulated Supply From A Single 3V Battery Figure 6 shows a - 5V power supply using one 3V - battery. The TC682 provides - 6V at VOUT, which is regulated to - 5V by the negative LDO. The input to the TC682 can vary from 3V to 5.5V without affecting regulation appreciably. A TC54 device is connected to the battery to detect undervoltage. This unit is set to detect at 2.7V. With higher input voltage, more current can be drawn from the outputs of the TC682. With 5V at VIN, 10mA can be drawn from the regulated output. Assuming 150 source resistance for the - converter, with IL= 10mA, the charge pump will droop 1.5V. ROUT () 4085 2084 510 285 145 125 105 94 87 4-24 TELCOM SEMICONDUCTOR, INC. INVERTING VOLTAGE DOUBLER 1 TC682 VIN 2 + 10F - - C1 + C1 VIN 10F - - C1 + + C1 VIN TC682 + 10F - - C2 GND + C2 V- OUT TC682 + 10F - C+ 2 - C2 - VOUT GND NEGATIVE SUPPLY - + - COUT 22F 3 4 GND Figure 5. Paralleling TC682 for Lower Output Source Resistance 5 + 10F - + 3V - + 10F - - C1 + C2 - C2 GND + C1 VIN TC682 VSS VOUT - 22F +C - OUT + - VOUT 1F GROUND - 6 -5 SUPPLY VIN NEGATIVE LDO REGULATOR TC54VC2702Exx VIN VSS VOUT LOW BATTERY 7 Figure 6. Negative Supply Derived from 3V Battery 8 4-25 TELCOM SEMICONDUCTOR, INC. INVERTING VOLTAGE DOUBLER TC682 TYPICAL CHARACTERISTICS (FOSC = 12kHz) Output Resistance vs. VIN 240 C1- C3 = 3.3F OUTPUT RESISTANCE () VOUT vs. Load Current -7.5 -8.0 -8.5 VOUT (V) VIN = 5V 220 200 180 160 140 120 1 2 3 VIN (V) Supply Current vs. VIN OUTPUT SOURCE RESISTANCE () -9.0 -9.5 -10.0 -10.5 4 5 6 0 5 10 15 LOAD CURRENT (mA) Output Source Resistance vs. Temperature 200 180 160 140 120 100 80 -50 VIN = 5V IOUT = 10mA 300 NO LOAD SUPPLY CURRENT (A) 250 200 150 100 50 1 2 3 VIN (V) 4 5 6 0 50 100 TEMPERATURE (C) Output Ripple vs. Output Current 200 OUTPUT RIPPLE (mV PK-PK) VIN = 5V 150 C3 =10F 100 50 C3 =100F 0 0 5 10 OUTPUT CURRENT (mA) 15 20 4-26 TELCOM SEMICONDUCTOR, INC. |
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