Datasheet MAX1682, MAX1683 (Maxim) - 7

Switched-Capacitor Voltage Doublers MAX1682/MAX1683 Cascading Devices Paralleling Devices
Devices can be cascaded to produce an even larger Paralleling multiple MAX1682 or MAX1683s reduces voltage (Figure 3). The unloaded output voltage is nom- the output resistance. Each device requires its own inally (n + 1) x VIN, where n is the number of voltage pump capacitor (C1), but the reservoir capacitor (C2) doublers used. This voltage is reduced by the output serves all devices (Figure 4). Increase C2’s value by a resistance of the first device multiplied by the quiescent factor of n, where n is the number of parallel devices. current of the second. The output resistance increases Figure 4 shows the equation for calculating output when devices are cascaded. Using a two-stage dou- resistance. bler as an example, output resistance can be approxi- mated as R
Layout and Grounding
OUT = 2 x ROUT1 + ROUT2, where ROUT1 is the output resistance of the first stage and R Good layout is important, primarily for good noise per- OUT2 is the output resistance of the second stage. A typical value formance. To ensure good layout, mount all compo- for a two-stage voltage doubler is 60Ω (with C1 at 10µF nents as close together as possible, keep traces short for MAX1682 and 3.3µF for MAX1683). For n stages to minimize parasitic inductance and capacitance, and with the same C1 value, R use a ground plane. OUT = (2n - 1) x ROUT1. INPUT SUPPLY INPUT VOLTAGE SUPPLY VOLTAGE C1+ IN IN C1+ C1+ IN IN C1+ MAX1682 MAX1683 MAX1682 MAX1682 MAX1682 GND MAX1683 GND MAX1683 MAX1683 C1 C1 GND GND OUTPUT C1 C1 VOLTAGE OUTPUT C1- OUT VOLTAGE C1- OUT C1- OUT C2 C1- OUT C2 R R OUT OF SINGLE DEVICE OUT = C2 NUMBER OF DEVICES Figure 3. Cascading Devices Figure 4. Paralleling Devices
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