SP3221ECA SIPEX [Sipex Corporation], SP3221ECA Datasheet - Page 13

• Manufacturer Part Number: SP3221ECA
• Description: Intelligent +3.0V to +5.5V RS-232 Transceiver
• Manufacturer: SIPEX [Sipex Corporation]

Date: 7/21/04
Auto-Online Circuitry
The SP3221E device has an Auto-Online cir-
cuitry on board that saves power in the system
the device is designed into without changes to
the existing BIOS or operating system.
The SP3221E device incorporates an
Auto-Online circuit that automatically
enables itself when the cable is connected to
another RS232 device. Conversely, the Auto-
Online circuit also disables most of the internal
circuitry when the cable is disconnected and
goes into a standby mode where the device
typically draws 1µA. This function is controlled
by the ONLINE pin. When this pin is tied to a
logic LOW, the Auto-Online function is active.
When the cable is disconnected, the receiver
inputs will be pulled down by its internal 5kΩ
resistors to ground. When ONLINE is HIGH,
the Auto-Online mode is disabled.
When the SP3221E driver or internal charge
pump are disabled, the supply current is reduced
to 1µA.
The Auto-Online mode can be overridden 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 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 cable is connected
to another RS232 device.
When the SP3221E device is shutdown, the
charge pump is turned off. V+ charge pump
output decays to V
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.
CC
, the V- output decays to
SP3221E +3.0V to +5.5V RS-232 Transceiver
13
Tying ONLINE and SHUTDOWN together
will bypass the Auto-Online circuitry so this
connection acts like a shutdown input pin.
© Copyright 2004 Sipex Corporation