SP3223E_06 Datasheet, PDF (12/23 Pages) Sipex Corporation – Intelligent +3.0V to +5.5V RS-232 Transceivers

The AUTO ON-LINE^® circuit has two stages:
1) Inactive Detection
2) Accumulated Delay
The first stage, shown in Figure 20, detects an
inactive input. A logic HIGH is asserted on
R INACT if the cable is disconnected or the
X
external transmitters are disabled. Otherwise,
R_XINACT will be at a logic LOW. This circuit
is duplicated for each of the other receivers.
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 SP3223 driver and receiver
outputs can be found in Table 2.
The clock rate for the charge pump typically
operates at above 250kHz. The external capaci-
tors can be as low as 0.1µF with a 16V break-
down voltage rating.
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 en-
abled and the cable is connected.
The second stage of the AUTO ON-LINE^®
circuitry, shown in Figure 21, processes all the
receiver's R_XINACT signals with an accumu-
lated delay that disables the device to a 1µA
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
20µs.
When the SP3223 drivers or internal charge
pump are disabled, the supply current is reduced
to 1µA. This can commonly occur in handheld
RECEIVER ^+2.7V
RS-232 INPUT ^0V
VOLTAGES -2.7V
VCC
STATUS
0V
tSTSL
+5V
DRIVER
RS-232 OUTPUT _0V
VOLTAGES
-5V
When the SP3223 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 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 AUTO ON-LINE^®
circuitry so this connection acts like a shutdown
input pin
S
H
U
T
D
O
W
N
tSTSH
tONLINE
Figure 16. AUTO ON-LINE^® Timing Waveforms
Date: 10/06/06
SP3223 +3.0V to +5.5V RS-232 Transceivers
12
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