In most circumstances, decoupling the power

supply can be achieved adequately using

a 0.1µF bypass capacitor at C5 (refer to

figures 8 and 9)

In applications that are sensitive to power-

supply noise, decouple Vcc to ground with a

capacitor of the same value as charge-pump

capacitor C1. Physically connect bypass

capcitors as close to the IC as possible.

The charge pump operates in a discontinu-

ous mode using an internal oscillator. If the

output voltages are less than a magnitude

of 5.5V, the charge pump is enabled. If the

output voltages exceed a magnitude of 5.5V,

the charge pump is disabled. This oscillator

controls the four phases of the voltage shift-

ing. A description of each phase follows.

Phase 1

— V

of the clock cycle, the positive side of capaci-

tors C

C

l

in C

1

2

2

nected to V

capacitor C

Phase 2

— V

connects the negative terminal of C

storage capacitor and the positive terminal of

C

ated voltage to C

regulated to a minimum voltage of -5.5V.

Simultaneous with the transfer of the volt-

age to C

is switched to V

connected to GND.

Phase 3

— V

the clock is identical to the first phase — the

charge transferred in C

the negative terminal of C

to the negative side of capacitor C

Since

C

2

is 2 times V

Phase 4

— V

DD

transfer — The fourth phase of

the clock connects the negative terminal

of C

generated voltage across C

2

to C

the

V

DD

storage capacitor.

This voltage is

regulated to +5.5V. At this voltage, the in-

ternal oscillator is disabled. Simultaneous

with the transfer of the voltage to C

positive side of capacitor C

to V

the

negative side is con-

nected to GND, allowing

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.

ated from V

+

inefficiencies in the design.

The clock rate for the charge pump typically

operates at greater than 250kHz. The exter-

nal capacitors can be as low as 0.1µF with

a 16V breakdown voltage rating.

DESCRIPTION

10

Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7000 • www.exar.com

SP3222EB/SP3232EB_106_022316