SP3224E Datasheet, PDF (14/23 Pages) Sipex Corporation – 3.0V to 5.5V RS-232 Transceivers with Auto On-Line® Plus

that saves power by turning off the charge
pumps and driver outputs when the trans-
ceiver inputs are idle for more than 30 sec-
onds. Auto On-line^® Plus is equivalent to
Maxim’s “Auto Shutdown Plus” feature.It
differs from our existing Auto On-line^® by
relying on signal transitions rather than
voltage levels to trigger shutdown and
wakeup.
Auto On-Line^® Plusautomatically puts the
device into a standby mode where it draws
only 1μA typical.When the device detects
activity on either the receiver or driver in-
puts it will automatically awake and activate
to allow serial communication. Both the
wakeup and shutdown happen automati-
Receiver
5kΩ
THEORY OF OPERATION
logic LOW forces the device into shutdown
state regardless of input activity or the sta-
tus of the ONLINE pin.
The STATUS output determines whether a
valid RS-232 signal voltage is present on
the inputs.The STATUS pin goes to a logic
LOW when the receiver input signal levels
collapse near reference ground. This may
occur when the RS-232 cable is discon-
nected or the RS-232 drivers of the con-
nected peripheral are turned off.
STATUS may be used to indicate DTR or a
Ring Indicator signal or to determine wheth-
er a live RS232 driver or cable is connect-
ed. By connecting the STATUS output to
ONLINE input, the SP3224E-SP3227E will
shut down when no valid signal level and
no input transitions are detected, and wake
up on a valid signal level or signal edge.If it
detects no signal transitions with the past 30
+0.3V
R_IN
-0.3V
T_IN EDGE
DETECT
30µs
timer
STATUS
R_IN EDGE
DETECT
SHUTDOWN
S
30s
timer
A
AUTO ONLINE
INVALID ASSERTED IF ALL RECEIVER INPUTS ARE
BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µS
Figure 3a.STATUS Functional Diagram STATUS low
ONLINE
Figure 3c. Auto On-line^¨ Plus Logic
+2.7V
SHUTDOWN
POWERDOWN
R_IN
-2.7V
30µs
timer
STATUS
INVALID DEASSERTED IF ALL RECEIVER INPUTS ARE
BETWEEN +2.7V AND -2.7V FOR AT LEAST 30µS
ONLINE
AUTO ONLIN E
POWERDOWN IS ONLY A INTERNAL SIGNAL. IT
CONTROLS THE OPERATIONAL STATUS TO THE
TRANSMITTERS AND THE POWER SUPPLIES.
Figure 3b. STATUS Functional Diagram, STATUS high. ^{Figure 3d. Powerdown Logic}
cally, without any user intervention, special
drivers, or software modifications.
Wakeup and shutdown can be exter-
nally controlled by the ONLINE and
SHUTDOWN pins.When ONLINE is driv-
en to logic LOW, the Auto On-line^® Plus
function is active.Driving SHUTDOWN to
seconds, the device will go into low power
mode. By connecting the STATUS output to
both the ONLINE input and SHUTDOWN
input pins, the device enters into shutdown
when not receiving a valid RS-232 signal voltage
input.
When the SP3224E-SP3227E devices are
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
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