SP3243EHCT datasheet(17/24 Pages) SIPEX

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SP3223EHDS/11

SP3223EH +3.0V to +5.5V RS-232 Transceivers

Auto-Online Circuitry

The SP3223EH and SP3243EH devices have a

patent pending Auto-Online circuitry on board

that saves power in applications such as laptop

computers, palmtop (PDA) computers and other

portable systems.

The SP3223EH and SP3243EH devices

incorporate an

Auto-Online circuit that

automatically enables itself when the external

transmitters are enabled and the cable is

connected. Conversely, the Auto-Online 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

µA. This function can also be externally

controlled by the ONLINE pin. When this pin is

tied to a logic LOW, the Auto-Online 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-Online mode is disabled.

The Auto-Online 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-Online circuitry,

shown in Figure 24, processes all the receiver's

XINACT signals with an accumulated 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 SP3223EH and SP3243EH 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-Online mode can be disabled by the

SHUTDOWN pin. If this pin is a logic LOW,

the Auto-Online function will not operate

regardless of the logic state of the ONLINE pin.

Table 3 summarizes the logic of the Auto-Online

operating modes. The truth table logic of the

SP3223EH and SP3243EH 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 SP3223EH and SP3243EH 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-Online circuitry so this

connection acts like a shutdown input pin.

SP3243EHCT 数据表(PDF) 17 Page - Sipex Corporation

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