ADP3605

Data Sheet

Rev. B | Page 8 of 12

THEORY OF OPERATION

The ADP3605 uses a switched capacitor principle to generate a

negative voltage from a positive input voltage. An onboard

oscillator generates a 2-phase clock to control a switching

network that transfers charge between the storage capacitors. The

switches turn on and off at a 250 kHz rate, which is generated

from an internal 500 kHz oscillator. The basic principle behind

the voltage inversion scheme is illustrated in Figure 12 and

Figure 13.

Figure 12. ADP3605 Switch Configuration Charging the Pump Capacitor

During phase one, S1 and S2 are on, charging the pump capacitor

to the input voltage. Before the next phase begins, S1 and S2 are

turned off as well as S3 and S4 to prevent any overlap. S3 and S4

are turned on during the second phase (see Figure 13), and the

charge stored in the pump capacitor is transferred to the output

capacitor.

Figure 13. ADP3605 Switch Configuration Charging the Output Capacitor

During the second phase, the positive terminal of the pump

capacitor is connected to ground through the variable resistance

switch (S3), and the negative terminal is connected to the output,

resulting in a voltage inversion at the output terminal. Figure 1

shows the ADP3605 block diagram.

+

S1

S2

S3

S4

+

S1

S2

S3

S4