MAX3238CAIT Maxim Integrated Products, Inc., MAX3238CAIT Datasheet - Page 6

• Manufacturer Part Number: MAX3238CAIT
• Description: Max3238 +3.0v To +5.5v, 1?a, Up To 250kbps, True Rs-232 Transceiver With Autoshutdown Plus
• Manufacturer: Maxim Integrated Products, Inc.

+3.0V to +5.5V, 1µA, up to 250kbps, True
RS-232 Transceiver with AutoShutdown Plus
Figure 1. Interface Under Control of PMU
1µA supply current is achieved with Maxim’s
AutoShutdown Plus feature, which operates when
FORCEOFF is high and FORCEON is low. When the
MAX3238 senses no valid signal transitions on all
receiver and transmitter inputs for 30sec, the on-board
power supply and drivers are shut off, reducing supply
current to 1µA. This occurs if the RS-232 cable is dis-
connected or if the connected peripheral transmitters
are turned off. The system turns on again when a valid
transition is applied to any RS-232 receiver or transmit-
ter input. As a result, the system saves power without
changes to the existing BIOS or operating system. The
INVALID output is high when the receivers are active.
Since INVALID indicates the receiver inputs’ condition,
it can be used in any mode (Figure 3).
6
MANAGEMENT
CONTROLLER
CPU
_______________________________________________________________________________________
KEYBOARD
UNIT OR
POWER
WITH
UART
CHIP
INVALID
FORCEOFF
FORCEON
I/O
AutoShutdown Plus Mode
MAX3238
T1
T2
T3
T4
T5
R1
R2
R3
RS-232
Figure 2. The MAX3238 detects RS-232 activity when the
UART and interface are shut down.
(b)
(a)
OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
V
NEW MAX3238: IN SHUTDOWN, R1OUTB IS USED TO MONITOR EXTERNAL
DEVICES AND R1OUT IS THREE STATED, ELIMINATING A CURRENT PATH
THROUGH THE UART'S PROTECTION DIODE.
V
CC
CC
GND
UART
GND
UART
TO
P
PROTECTION
DIODE
PROTECTION
DIODE
Rx
Rx
Tx
Tx
TRANSITION
DETECTOR
LOGIC
SHDN = GND
FORCEOFF = GND
THREE-STATED
V
CC
I
V
R1OUTB
CC
R1OUT
T1IN
I
PREVIOUS
MAX3238
RS-232
5k
5k
R1IN
T1OUT