1 Features

• ESD Protection for RS-232 pins

– ±15-kV Human-body model (HBM)

– ±8-kV IEC 61000-4-2 Contact discharge

– ±15-kV IEC 61000-4-2 Air-gap discharge

• Operate with 3-V to 5.5-V VCC supply

• Operate up to 1 Mbit/s

• Low Standby Current . . . 1 μA Typical

• External capacitors . . . 4 × 0.1 μF

• Accepts 5-V logic input with 3.3-V supply

• RS-232 Bus-pin esd protection exceeds ±15 kv

using human-body model (HBM)

• Auto-powerdown feature automatically disables

drivers for power savings

2 Applications

• Industrial PCs

• Wired networking

• Data center and enterprise computing

• Battery-powered systems

• PDAs

• Notebooks

• Laptops

• Palmtop PCs

• Hand-held equipment

3 Description

The SN65C3221E and SN75C3221E consist of one

line driver, one line receiver, and a dual charge-pump

circuit with ±15-kV IEC ESD protection pin to pin

(serial-port connection pins, including GND). These

devices provide the electrical interface between

an asynchronous communication controller and the

serial-port connector. The charge pump and four small

external capacitors allow operation from a single

3-V to 5.5-V supply. These devices operate at data

signaling rates up to 1 Mbit/s and a driver output slew

rate of 24 V/μs to 150 V/μs.

Flexible control options for power management are

available when the serial port is inactive. The autopowerdown

feature functions when FORCEON is

low and FORCEOFF is high. During this mode of

operation, if the devices do 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. Autopowerdown

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. See Figure 8-5 for receiver input

levels.