Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-707 • www.exar.com

SP3203E_00_2080

8

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

outputvoltages exceedamagnitudeof5.5V,

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

+

is then switched to GND and the charge

in C



–

is transferred to C

2

–

. Since C

2

+

is con-

nected to V

capacitor C

Phase 2

— V

connectsthenegativeterminalofC

storagecapacitorandthepositiveterminalof

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

C

2

+

is at V

is 2 times V

Table 2. SHUTDOWN Truth Tables

(Note: When the device is shutdown, the SP3203E's

charge pump is turned off and V+ decays to Vcc, V- is

pulledtogroundandthetransmitteroutputsaredisabled

as High Impedance.)

Figure 2. Loopback Test Circuit for RS-232 Driver

Data Transmission Rates

Phase 4

— V

the clock connects the negative terminal

of C

generated voltage across C

V

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

positivesideofcapacitorC

and the negative side is switched to GND, al-

lowingthechargepumpcycletobeginagain.

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.

V

Device: SP3203E

SHUTDOWN T

R

Charge

Pump

0

High-Z

High-Z

Inactive



Active

Active

Active

SP3203E

1

3

5

4

2

6

19

GND

C1+

C1-

C2+

C2-

V+

V-

+

C2

C5

C1

+

+

C3

C4

+

+

0.1µF

TTL/CMOS

INPUTS

+3V to +5V

18

SHUTDOWN

20

5KΩ

5KΩ

TTL/CMOS

OUTPUTS

1000pF

1000pF

12

VL

+3V to +5.5V

0.1µF

0.1µF

0.1µF

0.1µF