SP3243ECT datasheet(17/24 Pages) SIPEX

17 / 24 page

Rev. 11/14/02

SP3223E +3.0V to +5.5V RS-232 Transceivers

AUTO ON-LINE® Circuitry

The SP3223E and SP3243E devices have a

patent pending AUTO ON-LINE® circuitry on

board that saves power in applications such as

laptop computers, palmtop (PDA) computers,

and other portable systems.

The SP3223E and SP3243E devices incorporate

an AUTO ON-LINE® circuit that automati-

cally enables itself when the external transmit-

ters are enabled and the cable is connected.

Conversely, the AUTO ON-LINE® circuit also

disables most of the internal circuitry when the

device is not being used and goes into a standby

mode where the device typically draws 1

µA.

This function can also be externally controlled

by the ONLINE pin. When this pin is tied to a

logic LOW, the AUTO ON-LINE® function is

active. Once active, the device is enabled until

there is no activity on the receiver inputs. The

receiver input typically sees at least

±3V, which

are generated from the transmitters at the other

end of the cable with a

±5V minimum. When the

external transmitters are disabled or the cable is

disconnected, the receiver inputs will be pulled

down by their internal 5k

Ω resistors to ground.

When this occurs over a period of time, the

internal transmitters will be disabled and the

device goes into a shutdown or standy mode.

When ONLINE is HIGH, the AUTO ON-LINE®

mode is disabled.

The AUTO ON-LINE® circuit has two stages:

1) Inactive Detection

2) Accumulated Delay

The first stage, shown in Figure 23, detects an

inactive input. A logic HIGH is asserted on

XINACT if the cable is disconnected or the

external transmitters are disabled. Otherwise,

XINACT will be at a logic LOW. This circuit

is duplicated for each of the other receivers.

The second stage of the AUTO ON-LINE®

circuitry, shown in Figure 24, processes all the

receiver's R

XINACT signals with an accumu-

lated delay that disables the device to a 1

µA

supply current.

The STATUS pin goes to a logic LOW when the

cable is disconnected, the external transmitters

are disabled, or the SHUTDOWN pin is

invoked.

The typical accumulated delay is

around 20

µs.

When the SP3223E and SP3243E drivers or

internal charge pump are disabled, the supply

current is reduced to 1

µA. This can commonly

occur in hand-held or portable applications where

the RS-232 cable is disconnected or the RS-232

drivers of the connected peripheral are turned off.

The AUTO ON-LINE® mode can be disabled

by the SHUTDOWN pin. If this pin is a logic

LOW,the AUTO ON-LINE® function will not

operate regardless of the logic state of the

ONLINE pin. Table 3 summarizes the logic of the

AUTO ON-LINE® operating modes. The truth

table logic of the SP3223E and SP3243E driver

and receiver outputs can be found in Table 2.

The STATUS pin outputs a logic LOW signal

if the device is shutdown. This pin goes to a

logic HIGH when the external transmitters are

enabled and the cable is connected.

When the SP3223E and SP3243E devices

are shut down, the charge pumps are turned off.

V+ charge pump output decays to V

CC, the

V- output 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 200

µs.

For easy programming, the STATUS can be

used to indicate DTR or a Ring Indicator signal.

Tying ONLINE and SHUTDOWN together

will bypass the AUTO ON-LINE® circuitry so

this connection acts like a shutdown input pin.

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