±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
MAX3221E/MAX3223E/MAX3243E
Table 1. Output Control Truth Table
OPERATION
STATUS
FORCEON
FORCEOFF
EN
(MAX3221E/
MAX3223E)
VALID
RECEIVER
LEVEL
T_OUT
R_OUT
(MAX3221E/
MAX3223E)
R_OUT
(MAX3243E)
R2OUTB
(MAX3243E)
Shutdown
(Forced Off)
Normal Operation
(Forced On)
Normal Operation
(AutoShutdown)
Shutdown
(AutoShutdown)
X
X
1
1
0
0
0
0
0
0
1
1
1
1
1
1
0
1
0
1
0
1
0
1
X
X
X
X
Yes
Yes
No
No
High-Z
High-Z
Active
Active
Active
Active
High-Z
High-Z
Active
High-Z
Active
High-Z
Active
High-Z
Active
High-Z
High-Z
High-Z
Active
Active
Active
Active
High-Z
High-Z
Active
Active
Active
Active
Active
Active
Active
Active
X = Don’t Care
+0.3V
TO MAX32_ _E
POWER SUPPLY
AND TRANSMITTERS
INVALID
+2.7V
TO MAX32_ _E
POWER SUPPLY
INVALID
R_IN
R_IN
-0.3V
30µs
COUNTER
R
-2.7V
30µs
COUNTER
R
* TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR
AT LEAST
30µs.
* TRANSMITTERS ARE ENABLED IF:
ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V.
ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR
LESS THAN
30µs.
Figure 3a. MAX32_ _E Entering 1µA Supply Mode via
AutoShutdown
Figure 3b. MAX32__E with Transmitters Enabled Using
AutoShutdown
The MAX3221E/MAX3223E/MAX3243E feature an
INVALID
output that is enabled low when no valid RS-232
signal levels have been detected on all receiver inputs.
INVALID
is functional in any mode (Figures 3 and 5).
AutoShutdown
The MAX3221E/MAX3223E/MAX3243E achieve a 1µA
supply current with Maxim’s new AutoShutdown fea-
ture, which operates when FORCEON is low and
FORCEOFF
is high. When these devices sense no valid
signal levels on all receiver inputs for 30µs, the on-
board charge pump and drivers are shut off, reducing
supply current to 1µA. This occurs if the RS-232 cable
is disconnected or the connected peripheral transmit-
ters are turned off. The device turns on again when a
valid level is applied to any RS-232 receiver input. As a
result, the system saves power without changes to the
existing BIOS or operating system.
8
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
