3

Exar Corporation 48720 Kato Road, Fremont CA, 94538 • (50)668-707 • www.exar.com

SP3223E/EB/EU_0_06272

The

circuitry on board that saves power in ap-

plications such as laptop computers, PDA's,

and other portable systems.

The

SP3223 device incorporates an AUTO

itselfwhentheexternaltransmitterisenabled

and the cable is connected. Conversely,

the

most of the internal circuitry when the device

is not being used and goes into a standby

mode where the device typically draws µA.

This function is externally controlled by the

ONLINE pin. When this pin is tied to a logic

LOW, the

tive. Once active, the device is enabled until

there is no activity on receiver inputs. The

receiver input typically sees at least ±3V,

which are generated from the transmitter

at the other end of the cable with a ±5V

minimum. When the external transmitter is

disabled or the cable is disconnected, the

receiver input will be pulled down by its

internal 5kΩ resistor to ground. When this

occurs over a period of time, the internal

transmitters will be disabled and the device

goes into a shutdown or standby mode.

When the ONLINE pin is HIGH, the

AUTO

The

stages:

) Inactive Detection

2) Accumulated Delay

The first stage, shown in Figure 22, detects

an inactive input. A logic HIGH is asserted

on R

or the external transmitters are disabled.

Otherwise, R

This circuit is duplicated for each of the other

receivers.

The second stage of the

circuitry, shown in Figure 23, processes

the receiver's R

cumulated delay that disables the device to

a µA typical supply current. The STATUS

pin goes to a logic LOW when the cable

is disconnected, the external transmit-

ter is disabled, or the SHUTDOWN pin is

invoked. The typical accumulated delay

is around 20µs. When the

SP3223 drivers

and internal charge pump are disabled, the

supply current is reduced to µA typical.

This can commonly occur in handheld or

portable applications where the RS-232

cable is disconnected or the RS-232 drivers

of the connected peripheral are truned off.

The

by the SHUTDOWN pin. If this pin is a logic

LOW, the

operate regardless of the logic state of the

ONLINE pin. Table 5 summarizes the logic

of the

Thetruthtablelogicofthe

SP3223driverand

receiver outputs can be found in Table 3.

The STATUS pin outputs a logic LOW signal

if the device is shutdown. This pin goes to

a logic HIGH when the external transmitter

is enabled and the cable is connected.

When the

SP3223 device is shutdown, the

charge pumps are turned off. V+ charge

pump output decays to V

decays to GND. The decay time will depend

on the size of capacitors used for the charge

pump. Once in shutdown, the time required

to exit the shut down state and have valid

V+ and V- levels is typically 200µs.

For easy programming, the STATUS can

be used to indicate DTR or a Ring Indicator

signal. Tying ONLINE and SHUTDOWN

together will bypass the

circuitry so this connection acts like a shut-

down input pin