13.24.1.3 Charge Pump Output Capacitor

Solve for the charge pump output capacitance, connected between V12P and ground, that will supply the 20 mA load for one switch cycle. The V_BOOT LDO pin on the dsPIC33CDVL256MC506 is the “V12P” pin referenced in the calculations.

C = I_OUT × dt/dV
C = I_OUT  13.3 µs/(V_DROP + I_OUT × C_ESR)
C = 20 mA  13.3 µs/(0.1V + 20 mA  20 m)
C ≥ 2.65 µF

For stability reasons, the V_BOOT LDO and V_REG LDO capacitors must be at least 4.7 µF, so choose: C ≥ 4.7 µF.

DS70005628A

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