±15kV ESD-Protected, 1µA, 1Mbps, 3.0V to 5.5V,
RS-232 Transceivers with AutoShutdown Plus
MAX3224E–MAX3227E/MAX3244E/MAX3245E
†
Table 1. Output Control Truth Table
OPERATION
STATUS
FORCEOFF
VALID
RECEIVER
LEVEL
RECEIVER OR
TRANSMITTER
EDGE WITHIN
30sec
X
R_OUT
(MAX3224E/
MAX3225E/
MAX3226E/
MAX3227E)
Active
R_OUT
(MAX3244E/
MAX3245E)
R2OUTB
(MAX3244E/
MAX3245E)
FORCEON
T_OUT
Shutdown
(Forced Off)
Normal
Operation
(Forced On)
Normal
Operation
(AutoShutdown
Plus)
Shutdown (Auto-
Shutdown Plus)
Normal
Operation
Normal
Operation
Shutdown
Normal
Operation
(AutoShutdown)
Shutdown
(AutoShutdown)
X = Don’t care
X
0
X
High-Z
High-Z
Active
1
1
X
X
Active
Active
Active
Active
0
1
X
Yes
Active
Active
Active
Active
0
INVALID*
INVALID*
INVALID*
INVALID*
1
1
1
1
INVALID**
X
Yes
X
No
Yes
No
X
Yes
No
X
High-Z
Active
Active
High-Z
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
INVALID*
INVALID**
No
X
High-Z
Active
High-Z
Active
*
INVALID
connected to FORCEON
**
INVALID
connected to FORCEON and
FORCEOFF
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 a1µA 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 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
peripheral transmitters are turned off, and the UART dri-
ving the transmitter inputs is inactive. The system turns
on again when a valid transition is applied to any
RS-232 receiver or transmitter input. As a result, the sys-
9
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
