Datasheet

RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3224–MAX3227 feature inverting
outputs that always remain active (Table 1). The
MAX3244/MAX3245 have inverting three-state outputs
that are high impedance when shut down (FORCEOFF
= GND) (Table 1).
The MAX3244/MAX3245 feature an extra, always
active, noninverting output, R2OUTB. R2OUTB output
monitors receiver activity while the other receivers are
high impedance, allowing Ring Indicator applications to
be monitored without forward biasing other devices
connected to the receiver outputs. This is ideal for sys-
tems where V
CC
is set to ground in shutdown to
accommodate peripherals such as UARTs (Figure 2).
The MAX3224–MAX3227/MAX3244/MAX3245 feature
an INVALID output that is enabled low when no valid
RS-232 voltage levels have been detected on all receiv-
er inputs. Because INVALID indicates the receiver
input’s condition, it is independent of FORCEON and
FORCEOFF states (Figures 3 and 4).
AutoShutdown Plus Mode
The MAX3224–MAX3227/MAX3244/MAX3245 achieve a
1µA supply current with Maxim’s AutoShutdown Plus
feature, which operates when FORCEOFF is high and a
FORCEON is low. When these devices do not sense a
valid signal transition on any receiver and transmitter
input for 30sec, the on-board charge pumps are shut
down, reducing supply current to 1µA. This occurs if the
RS-232 cable is disconnected or if the connected
1µA Supply Current, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
Table 1. Output Control Truth Table
OPERATION
STATUS
FORCEON
FORCEOFF
VALID
RECEIVER
LEVEL
RECEIVER OR
TRANSMITTER
EDGE WITHIN
30sec
T_OUT
R_OUT
(MAX3224/
MAX3225/
MAX3226/
MAX3227)
R_OUT
(MAX3244/
MAX3245)
R2OUTB
(MAX3244/
MAX3245)
Shutdown
(Forced Off)
X 0 X X High-Z Active High-Z Active
Normal
Operation
(Forced On)
1 1 X X Active Active Active Active
Normal
Operation
(AutoShutdown
Plus)
0 1 X Yes Active Active Active Active
Shutdown (Auto-
Shutdown Plus)
0 1 X No High-Z Active Active Active
Normal
Operation
INVALID*
1 Yes X Active Active Active Active
Normal
Operation
INVALID*
1 X Yes Active Active Active Active
Shutdown
INVALID*
1 No No High-Z Active Active Active
Normal
Operation
(AutoShutdown)
INVALID* INVALID**
Yes X Active Active Active Active
Shutdown
(AutoShutdown™)
INVALID* INVALID**
No X High-Z Active High-Z Active
X = Don’t care
* INVALID connected to FORCEON
** INVALID connected to FORCEON and FORCEOFF
AutoShutdown is a trademark of Maxim Integrated Products, Inc.
Maxim Integrated
9
MAX3224–MAX3227/MAX3244/MAX3245