1 µA S u p p ly Cu rre n t , 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
POWER-
MANAGEMENT
UNIT OR
KEYBOARD
CONTROLLER
FORCEOFF
FORCEON
INVALID
V
CC
PROTECTION
DIODE
PREVIOUS
RS-232
MAX3244
MAX3245
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
Figure 1. Interface Under Control of PMU
MAX3244
MAX3245
I
PROTECTION
DIODE
R2OUTB
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
V
CC
R2IN
Rx
R2OUT
THREE-STATED
UART
–7/MAX3245
5k
T1OUT
T1IN
GND or V
.
Tx
CC
RS -2 3 2 Re c e ive rs
GND
FORCEOFF = GND
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3224–MAX3227 feature inverting
outp uts tha t a lwa ys re ma in a c tive (Ta b le 1). The
MAX3244/MAX3245 have inverting three-state outputs
that are high impedance when shut down (FORCEOFF
= GND) (Table 1).
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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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
