SP782 データシートの表示（PDF） - Signal Processing Technologies

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SP782

Programmable Charge Pump

Signal Processing Technologies 

SHUTDOWN MODE

The internal oscillator of the SP782 and SP784

can be shutdown through the SD pin. In this

state, the VDD and VSS outputs are inactive and

the power supply current reduces to 10µA.

LATCH ENABLE PIN

The SP782 and SP784 includes a control pin

(LAT) that latches the D0 and D1 control lines.

Connecting this pin to a logic HIGH state will

allow transparent operation of the D0 and D1

control lines. This input can be left floating

since there is an internal pull-up resistor which

will allow the latch to be transparent.

APPLICATIONS INFORMATION

The SP782 and SP784 can be used in various

applications where ±10V is needed from a +5V

source. Analog switches, op-amp power sup-

plies, and LCD biasing are some applications

where the charge pumps can be used.

The charge pump can also be used for supplying

voltage rails for RS-232 drivers needing ±12V.

The ±10V output from the charge pump is more

than adequate to provide the proper VOH and

VOL levels at the driver output.

Figure 8 shows how the SP784 can be used

in conjunction with the SP524 multiprotocol

transceiver IC. The programmability is ideal for

RS-232 and RS-423 levels. The RS-232 driver

output voltage swing ranges from ±5V to ±15V.

In order to meet this requirement, the charge

pump must generate ±10V to the transceiver IC.

The RS-423 driver output voltage range is

±4.0V to ±6.0V. When the SP524 transceiver is

programmed to RS-423 mode (V.10), the charge

pump now provides ±5V, through D0 and D1,

thus allowing the driver outputs to comply with

VOC ≤ 6.0V as well as the VT requirement of

±4.0V minimum with a 450Ω load to ground.

In older configurations, separate DC sources

needed to be configured or regulated down from

±10V to ±5V in a given application. A typical

charge pump providing VDD and VSS would

require external clamping such as 5V Zener

diodes. RS-423 (V.10) is usually found in

RS-449, EIA-530, EIA-530A, and V.36 modes.

When the control lines D0 and D1 are both at a

logic HIGH, VDD = +5V and VSS = -5V. All

other inputs to the control lines result in VDD =

+10V and VSS = -10V. Control of the SP784 in

an application with Sipex's SP524 can be found

in Figure 8.

SP782/SP784 DS/08

SP782/784 Programmable Charge Pump

11

© Copyright 2000 Sipex Corporation

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