1µA Supply Current, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
MAX3224–MAX3227/MAX3244/MAX3245
†
POWER-
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
PROTECTION
DIODE
V
CC
MAX3244
MAX3245
V
CC
Rx
UART
Tx
GND
SHDN = GND
I
PREVIOUS
RS-232
5kΩ
CPU
I/O
CHIP
WITH
UART
RS-232
a)
OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
V
CC
TO
μP
LOGIC
TRANSITION
DETECTOR
Figure 1. Interface Under Control of PMU
PROTECTION
DIODE
I
MAX3244
MAX3245
RS-232 Transmitters
The transmitters are inverting level translators that
convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3224/MAX3226/MAX3244 guarantee a
250kbps data rate (1Mbps for the MAX3225/MAX3227/
MAX3245) with worst-case loads of 3kΩ in parallel with
1000pF, providing compatibility with PC-to-PC com-
munication software (such as LapLink™). Transmitters
can be paralleled to drive multiple receivers. Figure 1
shows a complete system connection.
When
FORCEOFF
is driven to ground or when the Auto-
Shutdown Plus circuitry senses that all receiver and
transmitter inputs are inactive for more than 30sec, the
transmitters are disabled and the outputs go into a high-
impedance state. When powered off or shut down, the
outputs can be driven to ±12V. The transmitter inputs
do not have pull-up resistors. Connect unused inputs to
GND or V
CC
.
R2OUTB
V
CC
Rx
UART
R2OUT
THREE-STATED
5kΩ
T1IN
FORCEOFF = GND
T1OUT
R2IN
Tx
GND
b)
NEW MAX3244/MAX3245: IN SHUTDOWN, R2OUTB IS USED TO MONITOR
EXTERNAL DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT
PATH THROUGH THE UART’S PROTECTION DIODE.
Figure 2. The MAX3244/MAX3245 detect RS-232 activity when
the UART and interface are shut down.
8
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