MAX3221

3V TO 5.5V SINGLECHANNEL RS232 LINE DRIVER/RECEIVER

WITH ±15kV ESD PROTECTION

SLLS348M − JUNE 1999 − REVISED MARCH 2004

2

POST OFFICE BOX 655303

description/ordering information (continued)

Flexible control options for power management are available when the serial port is inactive. The

auto-powerdown feature functions when FORCEON is low and FORCEOFF is high. During this mode of

operation, if the device does not sense a valid RS-232 signal on the receiver input, the driver output is disabled.

If FORCEOFF is set low and EN is high, both the driver and receiver are shut off, and the supply current is

reduced to 1

µA. Disconnecting the serial port or turning off the peripheral drivers causes the auto-powerdown

condition to occur. Auto-powerdown can be disabled when FORCEON and FORCEOFF are high. With

auto-powerdown enabled, the device is activated automatically when a valid signal is applied to the receiver

input. The INVALID output notifies the user if an RS-232 signal is present at the receiver input. INVALID is high

(valid data) if the receiver input voltage is greater than 2.7 V or less than −2.7 V, or has been between −0.3 V

and 0.3 V for less than 30

µs. INVALID is low (invalid data) if the receiver input voltage is between −0.3 V and

0.3 V for more than 30

µs. Refer to Figure 5 for receiver input levels.

Function Tables

EACH DRIVER

INPUTS

OUTPUT

DIN

FORCEON

FORCEOFF

VALID RIN

RS-232 LEVEL

OUTPUT

DOUT

DRIVER STATUS

X

X

L

X

Z

Powered off

L

H

H

X

H

Normal operation with

H

HH

X

L

Normal operation with

auto-powerdown disabled

L

L

H

Yes

H

Normal operation with

H

LH

Yes

L

Normal operation with

auto-powerdown enabled

L

L

H

No

Z

Powered off by

H

L

H

No

Z

Powered off by

auto-powerdown feature

H = high level, L = low level, X = irrelevant, Z = high impedance

EACH RECEIVER

INPUTS

OUTPUT

RIN

EN

VALID RIN

RS-232 LEVEL

OUTPUT

ROUT

L

L

X

H

H

LX

L

X

HX

Z

Open

L

No

H

H = high level, L = low level, X = irrelevant,

Z = high impedance (off), Open = disconnected

input or connected driver off