Rainbow Electronics MAX13223E - Manual (Page 8)

MAX13223E
AutoShutdown
The MAX13223E achieves 1µA supply current with
Maxim’s AutoShutdown feature, which operates when
FORCEON is low and FORCEOFF is high. When the
device senses no valid signal levels on both receiver
inputs for > 30µs (typ), the onboard 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 transmitters are turned off. The
device turns on again when a valid level is applied to
either RS-232 receiver input. As a result, the system
saves power. Table 2 summarizes the MAX13223E’s
operating modes. FORCEON and FORCEOFF override
AutoShutdown. When neither control is asserted, the IC
selects between these states automatically, based on
receiver input levels. Figure 6a shows the input levels
and Figure 6b shows the timing diagram for
AutoShutdown operation.
Software-Controlled Shutdown
If direct software control is desired, INVALID can be
used to indicate a DTR or Ring indicator signal.
Connect FORCEOFF and FORCEON together to bypass
AutoShutdown; therefore, the line acts as a SHDN input.
±70V Fault-Protected, 3.0V to 5.5V,
2Tx/2Rx RS-232 Transceiver
8 _______________________________________________________________________________________
MAX13223E
UART
FORCEON
FORCEOFF
POWER-
MANAGEMENT
UNIT OR CPU INVALID
RS-232
Figure 5. Interface Under Control of PMU
Table 1. Receiver Control Truth Table
EN R_OUT
0 Active
1 High Impedence
RECEIVER INPUT
AutoShutdown, TRANSMITTER DISABLED,
1 µA SUPPLY CURRENT
-2.7V
b)
a)
-0.3V
+2.7V
+0.3V
0
INDETERMINATE
INDETERMINATE
TRANSMITTER ENABLED, INVALID HIGH
TRANSMITTER ENABLED, INVALID HIGH
t INVL t INVH
t WU
V+
V-
0
+2.7V
+0.3V
-0.3V
-2.7V
0
V CC
V CC
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
OUTPUT
(V)
INVALID
REGION
Figures 6a and 6b. Trip Levels for Entering and Exiting
AutoShutdown