Datasheet

AutoShutdown
A 1µA supply current is achieved with Maxim’s new
AutoShutdown feature, which operates when
FORCEON is low and FORCEOFF is high. When the
MAX3212 senses no valid signal level on any receiver
input for typically 30µs, the on-board power supply and
drivers shut down. Internal 5kΩ resistors pull the receiv-
er inputs to ground, disabling the transmitters and
reducing supply current to 1 µA when the device is in
AutoShutdown mode. This occurs if the RS-232 cable is
disconnected or if the connected peripheral transmit-
ters are turned off. The system 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. When using the
AutoShutdown feature, INVALID is high when the
device is on and low when the device is shut down. The
INVALID output indicates the condition of the receiver
inputs; INVALID can be used in any mode.
MAX3212
+2.7V to +3.6V-Powered, 1µA Supply Current,
3-Driver/5-Receiver, True RS-232 Transceiver
_______________________________________________________________________________________ 7
MAX3212
T1OUT
R5OUTB
Tx
5k
UART
V
CC
T1IN
LOGIC
TRANSITION
DETECTOR
R5IN
R5OUT
EN = LOW
SHDN = LOW
V
CC
TO
µP
Rx
PREVIOUS
RS-232
Tx
UART
SHDN = LOW
V
CC
V
CC
GND
Rx
5k
a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM
ACTIVE RECEIVER OUTPUT IN SHUTDOWN.
b) NEW MAX3212: EN SHUTS DOWN RECEIVER OUTPUTS (EXCEPT FOR R5OUTB)
SO NO CURRENT FLOWS TO UART IN SHUTDOWN. R5OUTB INDICATES RECEIVER 
ACTIVITY DURING SHUTDOWN WITH EN HIGH.
GND
ESD
PROTECTION
DIODE
ESD
PROTECTION
DIODE
POWER
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER

CPU
I/O
CHIP
WITH
UART
MAX3212
RS-232
FORCEOFF
FORCEON
INVALID
Figure 1. Interface Under Control of PMU
Figure 2. Detection of RS-232 Activity when the UART and
Interface Are Shut Down: MAX3212 (b) vs. Previous
Transceivers (a)