±1 5 k V ES D-P ro t e c t e d , 1 µA, 1 Mb p s , 3 .0 V t o 5 .5 V,
RS -2 3 2 Tra n s c e ive rs w it h Au t o S h u t d o w n P lu s
V
CC
POWER-
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
E
PROTECTION
DIODE
PREVIOUS
RS-232
MAX3244E
MAX3245E
V
CC
I
Rx
Tx
5k
UART
GND
SHDN = GND
I/O
CHIP
WITH
UART
CPU
RS-232
a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM ACTIVE
RECEIVER OUTPUT IN SHUTDOWN.
V
CC
TO
µP
LOGIC
TRANSITION
DETECTOR
MAX3244E
MAX3245E
I
Figure 1. Interface Under Control of PMU
PROTECTION
DIODE
R2OUTB
munication software (such as LapLink™). Transmitters
can be paralleled to drive multiple receivers. Figure 1
shows a complete system connection.
V
CC
R2IN
Rx
R2OUT
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
THREE-STATED
UART
5k
T1OUT
T1IN
Tx
GND
FORCEOFF = GND
GND or V
.
CC
–7E/MAX3245
RS -2 3 2 Re c e ive rs
b) NEW MAX3244E/MAX3245E: IN SHUTDOWN, R2OUTB IS USED TO MONITOR
EXTERNAL DEVICES AND R2OUT IS THREE STATED, ELIMINATING A CURRENT
PATH THROUGH THE UART'S PROTECTION DIODE.
The receivers convert RS-232 signals to CMOS-logic
outp ut le ve ls . The MAX3224E–MAX3227E fe a ture
inverting outputs that always remain active (Table 1).
The MAX3244E/MAX3245E have inverting three-state
Figure 2. The MAX3244E/MAX3245E detect RS-232 activity
when the UART and interface are shut down.
8
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
