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TC1237EUN Datasheet(PDF) 4 Page - Microchip Technology |
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TC1237EUN Datasheet(HTML) 4 Page - Microchip Technology |
4 / 10 page 4 Inverting Dual (–VIN, –2VIN) Charge Pump Voltage Converters with Shutdown TC1235 TC1236 TC1237 TC1235/6/7-1 3/24/00 © 2001 Microchip Technology Inc. DS21371A P2LOSS (2, 3, 4) = IOUT2 2 x R OUT2 where ROUT2 = [ 1 / [fOSC(C2) ] + 8RSWITCH2 + 4ESRC2 + ESRCOUT2 ] Equation 1b. The internal switch resistance for the first stage (i.e. RSWITCH1) is approximately 3Ω and the switch resistance for the second stage (i.e. RSWITCH2) is approximately 7Ω. The losses in the circuit due to factor (4) above are also shown in Equation 2a for stage 1 and Equation 2b for stage 2. The output voltage ripple for stage 1 is given by Equation 3a and the output voltage ripple for stage 2 is given by Equation 3b. PLOSS1 (4) = [ (0.5)(C1)(VIN 2 – V OUT1 2 ) + (0.5) (COUT1) (VRIPPLE1 2 - 2V OUT1 VRIPPLE1) ] x fOSC Equation 2a. PLOSS2 (4) = [ (0.5) (C2) (VIN 2 – V OUT2 2 ) + (0.5) (COUT2) (VRIPPLE2 2 - 2V OUT2 VRIPPLE2) ] x fOSC Equation 2b. VRIPPLE1 = [ IOUT1 / (fOSC) (COUT1) ] + 2 (IOUT1) (ESRCOUT1) Equation 3a. VRIPPLE2 = [ IOUT2 / (fOSC) (COUT2) ] + 2 (IOUT2) (ESRCOUT2) Equation 3b. Capacitor Selection In order to maintain the lowest output resistance and output ripple voltage, it is recommended that low ESR capacitors be used. Additionally, larger values of C1 and C2 will lower the output resistance and larger values of COUT1 and COUT2 will reduce output ripple. (See Equations 1a, 1b, 3a, and 3b). NOTE: For proper charge pump operation, C1 and COUT1 must have a voltage rating greater than or equal to VIN, while C2 and COUT2 must have a voltage rating greater than or equal to 2VIN. Table 1a shows various values of C1 and the corre- sponding output resistance values for VIN=5V @ +25°C for stage 1 and Table 1b shows various values of C2 and the corresponding output resistance values for VIN=5V @ +25°C for stage 2. It assumes a 0.1 Ω ESRC1, a 0.1Ω ESRC2, a 3Ω RSWITCH1, and a 7Ω RSWITCH2. Table 2a shows the output voltage ripple for various values of COUT1 and Table 2b shows the output voltage ripple for various values of COUT2 (again assuming VIN = 5V @ +25 oC). The VRIPPLE1 values assume a 3mA output load current for stage 1 and a 0.1 Ω ESRCOUT1. The VRIPPLE2 values assume a 200 µA output load current for stage 2 and a 0.1 Ω ESRCOUT1. Table 1a. Output Resistance vs. C1 (ESR = 0.1 Ω). For Stage 1 C1 ( µF) TC1235 R OUT ( Ω) TC1236 R OUT ( Ω) TC1237 R OUT ( Ω) 0.47 202 85 42 1 108 53 33 3.3 50 33 27 Table 1b. Output Resistance vs. C2 (ESR = 0.1 Ω). For Stage 2 C2 ( µF) TC1235 ROUT (Ω) TC1236 ROUT (Ω) TC1237 ROUT (Ω) 0.1 890 342 137 0.47 239 117 74 1 140 85 65 Table 2a. Output Voltage Ripple vs. COUT1 (ESR = 0.1Ω) For Stage 1 (IOUT1 = 3mA) COUT1 TC1235 VRIPPLE1 TC1236 VRIPPLE1 TC1237 VRIPPLE1 ( µF) (mV) (mV) (mV) 0.47 533 183 52 1 251 86 25 3.3 76 27 8 Table 2b. Output Voltage Ripple vs. COUT2 (ESR = 0.1Ω) For Stage 2 (IOUT2 = 200 µA) COUT2 TC1235 VRIPPLE2 TC1236 VRIPPLE2 TC1237 VRIPPLE2 ( µF) (mV) (mV) (mV) 0.1 167 57 16 0.47 36 12 3.4 1 17 5.8 1.6 |
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