SP230ACT datasheet(8/17 Pages) SIPEX

8 / 17 page

Date: 8/3/04

+ 5V Powered Multi-Channel RS-232 Drivers/Receivers

ENABLE Input (EN)

The SP235A/B, SP236A/B, SP240A/B, and

SP241A/B all feature an enable input (EN),

which allows the receiver outputs to be either

tri–stated or enabled. The enable input is active

low; 0V applied to EN will enable the receiver

outputs. This can be especially useful when the

receiver is tied directly to a microprocessor data

bus.

Protection From Shorts to >±15V

The driver outputs are protected against shorts

to ground, other driver outputs, and V+ or V-.

For protection against voltages exceeding

±15V,

two back–to–back zener diodes connected to

clamp the outputs to an acceptable voltage level

are recommended. (Refer to Figure 3.)

Improved Drive Capability for Mouse

Applications

Each of the devices in this data sheet have

improved drive capability for non-standard ap-

plications. Although the EIA RS-232D stan-

dards specify the maximum loading to be 3k

Ω

and 2500pF, the SP230A, SP234A, SP235A/B,

SP236A/B, SP237A, SP238A, SP240A/B, and

SP241A/B can typically drive loads as low as

Ω and still maintain ±5V outputs. This feature

is especially useful when the serial port is in-

tended to be used for a “self-powered” mouse.

In this case the voltage necessary to operate the

circuits in the mouse can be derived from the

RS-232 driver output as long as the loading is

≥1kΩ (refer to Figure 4). For applications which

even exceed this requirement, drivers can be

connected in parallel, increasing the drive capa-

bility to 750

Ω, while maintaining the ±5V V

and V

OL levels (refer to Figure 5).

Power

Up/Down

Receiver

Outputs

Down

Enable

Tri–state

Enable

Tri–state

Figure 3. High Voltage Short Circuit Protection

Figure 2. Charge Pump Voltage Inverter

T IN

T OUT

15V ZENER

FROM

VOLTAGE DOUBLER

V+

V- = -(V+)

INTERNAL

OSCILLATOR

GND

output impedance of V+ and V-, which will

degrade V

OH and VOL. Capacitor values can be

as low as 1.0

µF.

Shutdown (SD)

TheSP230A, SP235A/B, SP236A/B, SP240A/

B and SP241A/B all feature a control input

which will disable the part and reduce V

current typically to less than 5

µA, which is

especially useful to designers of battery–pow-

ered systems. In the “power–off” mode the

receiver and transmitter will both be tri-stated.

V+ will discharge to V

CC, and V

- will discharge

to ground.

For complete shutdown to occur and the 10

µA

current drain to be realized, the following con-

ditions must be met:

• +5.00V must be applied to the SD pin;

• ENABLE must either 0V, +5.0V or not connected;

• the transmitter inputs must be either +5.0V or not

connected;

• V

CC must be +5V;

• Receiver inputs must be >0V and <+5V

Please note that for proper operation, the SD

input pin must never be left floating.

Table 2. Wake–Up Truth Table

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