Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com

SP3249E_100_013111

9

Phase 2

— V

connects the negative terminal of C

storage capacitor and the positive terminal of

C

This transfers a negative gener-

ated voltage to C

regulated to a minimum voltage of -5.5V.

SimultaneouswiththetransferofthevoltagetoC

the positive side of capacitor C

and the negative side is connected to GND.

Phase 3

— V

clock is identical to the first phase — the charge

transferred in C

terminal of C

side of capacitor C

+

is at V

age potential across C

Phase 4

— V

connects the negative terminal of C

and transfers this positive generated voltage

across C

voltage is regulated to +5.5V. At this voltage,

the internal oscillator is disabled. Simultane-

ous with the transfer of the voltage to C

positive side of capacitor C

and the negative side is connected to GND, al-

lowing the charge pump cycle to begin again.

The charge pump cycle will continue as long

as the operational conditions for the internal

oscillator are present.

from V

+

be symmetrical. Older charge pump approaches

inherent inefficiencies in the design.

The clock rate for the charge pump typically

operates at 500kHz. The external capacitors

can be as low as 0.1µF with a 16V breakdown

voltage rating.

Figure 10. Charge Pump Waveform