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AMS682CP Datasheet(PDF) 3 Page - Advanced Monolithic Systems |
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AMS682CP Datasheet(HTML) 3 Page - Advanced Monolithic Systems |
3 / 7 page Advanced Monolithic Systems, Inc. www.advanced-monolithic.com Phone (925) 443-0722 Fax (925) 443-0723 AMS682 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 C 2 -. Since C2 + is at +5V, the voltage potential across capacitor C 2 is now -10V. - + C 3 + - C1 C2 SW2 -5V SW4 SW3 SW1 V IN =+5V V OUT + - 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 the 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. - + C 3 + - C1 C2 SW2 -10V SW4 SW3 SW1 V IN =+5V V OUT + - Figure 3. Charge Pump - Phase 2 MAXIMUM OPERATING LIMITS The AMS682 has on-chip zener diodes that clamp VIN to approximately 5.8V, and V - OUT to -11.6V. Exceeding the maximum supply voltage will potentially damage the chip. With an input voltage of 2V to 5.5V the AMS682 will operate over the entire operating temperature range. 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 AMS682, efficiency is as shown below: Voltage Efficiency = VOUT / (-2VIN ) VOUT = -2VIN + VDROP VDROP = (IOUT) (R OUT) Power Loss = IOUT (VDROP) There will be a substantial voltage difference between VOUT and 2VIN if the impedances of the pump capacitors C1 and C2 are high with respect to their respective output loads. If the values of the reservoir capacitor C3 are larger the output ripple will be reduced. The efficiency will be improved if both pump and reservoir capacitors have larger values. ( See “Capacitor Selection” in Application Section.) APPLICATIONS Negative Doubling Converter The AMS682 is most commonly used as a charge pump voltage converter which provides a negative output of two times a positive input voltage (Fig.4) GND V IN 6 4 V- OUT 5 7 2 3 1 C 1 - C 2 + C 1 + C 2 - GND V IN V- OUT C 3 22 µF + + + 22 µF 22 µF C 1 C 2 ON/OFF 8 Figure 4. Inverting Voltage Doubler |
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Similar Description - AMS682CP |
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