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.