MAX3243ECWI Maxim, MAX3243ECWI Datasheet - Page 9

• Manufacturer Part Number: MAX3243ECWI
• Description: 15kV ESD-Protected / 1A / 3.0V to 5.5V / 250kbps / RS-232 Transceivers with AutoShutdown
• Manufacturer: Maxim

Table 2 and Figure 3c summarize the MAX3221E/
MAX3223E/MAX3243E operating modes. FORCEON
and FORCEOFF override AutoShutdown. When neither
control is asserted, the IC selects between these states
automatically, based on receiver input levels. Figures
3a, 3b, and 5a depict valid and invalid RS-232 receiver
levels. Figure 5 shows the input levels and timing dia-
gram for AutoShutdown operation.
A mouse or other system with AutoShutdown may need
time to wake up. Figure 4 shows a circuit that forces the
transmitters on for 100ms, allowing enough time for the
other system to realize that the MAX3221E/MAX3223E/
MAX3243E are awake. If the other system transmits
valid RS-232 signals within that time, the RS-232 ports
on both systems remain enabled.
When shut down, the device’s charge pumps are off, V+
is pulled to V
mitter outputs are high impedance. The time required to
exit shutdown is typically 100µs (Figure 5b).
If direct software control is desired, INVALID can be
used to indicate DTR or Ring Indicator signal. Connect
FORCEOFF and FORCEON together to disable Auto-
Shutdown so the line acts like a SHDN input.
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System
Figure 3c. MAX32_ _E AutoShutdown Logic
INVALID IS AN INTERNALLY GENERATED SIGNAL
THAT IS USED BY THE AUTOSHUTDOWN LOGIC
AND APPEARS AS AN OUTPUT OF THE DEVICE.
POWER DOWN IS ONLY AN INTERNAL SIGNAL.
IT CONTROLS THE OPERATIONAL STATUS OF
THE TRANSMITTERS AND THE POWER SUPPLIES.
MANAGEMENT
POWER-
UNIT
FORCEOFF
FORCEON
INVALID
RS-232 Transceivers with AutoShutdown™
CC
, V- is pulled to ground, and the trans-
Software-Controlled Shutdown
MASTER SHDN LINE
_______________________________________________________________________________________
1µA Supply-Current, True +3V to +5.5V
FORCEOFF
MAX3221E
MAX3223E
MAX3243E
0.1µF
FORCEON
POWER DOWN
1M
Table 2. INVALID Truth Table
Figure 5. AutoShutdown Trip Levels
RECEIVER
VOLTAGE
RS-232 SIGNAL PRESENT
AT ANY RECEIVER INPUT
OUTPUT
INVALID
INPUT
b)
(V)
(V)
a)
V
V
+2.7V
+0.3V
CC
V+
CC
-0.3V
-2.7V
V-
0
0
0
Yes
No
AUTOSHUTDOWN, TRANSMITTERS DISABLED,
TRANSMITTERS ENABLED, INVALID HIGH
TRANSMITTERS ENABLED, INVALID HIGH
1 A SUPPLY CURRENT, INVALID LOW
t
INVL
INDETERMINATE
INDETERMINATE
INVALID OUTPUT
High
Low
t
INVH
INVALID
REGION
t
WU
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