Datasheet

MAX221
+5V, 1µA, Single RS-232 Transceiver
with AutoShutdown
6 _______________________________________________________________________________________
Table 1. Output Control Truth Table
1 No
Shutdown
(AutoShutdown)
High-Z1 High-Z0
1
1
1
OPERATION
STATUS
X0
VALID
RECEIVER
LEVEL
EN
X
Shutdown
(Forced Off)
X
Normal Operation
(Forced On)
X0
Yes
Normal Operation
(AutoShutdown)
No
Yes0
0
High-Z
Active
Active
High-Z
TOUT
Active
High-Z
Active
0
FORCEOFF
1
0
1
1
1
1
High-Z
High-Z
Active
Active
ROUT
High-Z
Active
Active
X
FORCEON
1
X
1
0
0
0
X = Don’t care
RS-232 SIGNAL PRESENT
AT RECEIVER INPUT
INVALID OUTPUT
Yes High
No Low
Table 2. INVALID Truth Table
+0.3V
-0.3V
INVALID
TO MAX221
POWER SUPPLY
AND TRANSMITTER
RIN
* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs.
30µs
COUNTER
R
+2.7V
-2.7V
INVALID
TO MAX221
POWER SUPPLY
RIN
* TRANSMITTER IS ENABLED IF:
RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;
RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30µs.
30µs
COUNTER
R
Figure 2b. Transmitter Enabled Using AutoShutdown
Figure 2a. Entering 1µA Supply Mode via AutoShutdown
FORCEOFF
POWER DOWN
INVALID
FORCEON
INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY
THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT.
POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE
OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES.
Figure 2c. AutoShutdown Logic