Datasheet

±15kV ESD-Protected, 1µA, 1Mbps 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3224E–MAX3227E feature
inverting outputs that always remain active (Table 1).
The MAX3244E/MAX3245E have inverting three-state
outputs that are high impedance when shut down
(FORCEOFF = GND) (Table 1).
The MAX3244E/MAX3245E 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 MAX3224E–MAX3227E/MAX3244E/MAX3245E fea-
ture an INVALID output that is enabled low when no
valid RS-232 voltage levels have been detected on all
receiver inputs. Because INVALID indicates the receiv-
er input’s condition, it is independent of FORCEON and
FORCEOFF states (Figures 3 and 4).
AutoShutdown Plus Mode
The MAX3224E–MAX3227E/MAX3244E/MAX3245E
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 trans-
mitter input for 30s, 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
Table 1. Output Control Truth Table
OPERATION
STATUS
FORCEON
FORCEOFF
VALID
RECEIVER
LEVEL
RECEIVER OR
TRANSMITTER
EDGE WITHIN
30s
T_OUT
R_OUT
(MAX3224E/
MAX3225E/
MAX3226E/
MAX3227E)
R_OUT
(MAX3244E/
MAX3245E)
R2OUTB
(MAX3244E/
MAX3245E)
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
10
Maxim Integrated
MAX3224E/MAX3225E/
MAX3226E/MAX3227E/MAX3244E/MAX3245E