MAX3221E Просмотр технического описания (PDF) - Maxim Integrated
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MAX3221E
Maxim Integrated
MAX3221E Datasheet PDF : 19 Pages
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MAX3221E/MAX3223E/MAX3243E
±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
Table 1. Output Control Truth Table
OPERATION
STATUS
FORCEON
FORCEOFF
EN
(MAX3221E/
MAX3223E)
Shutdown
X
0
0
(Forced Off)
X
0
1
Normal Operation
1
1
0
(Forced On)
1
1
1
Normal Operation
0
1
0
(AutoShutdown)
0
1
1
VALID
RECEIVER
LEVEL
X
X
X
X
Yes
Yes
T_OUT
High-Z
High-Z
Active
Active
Active
Active
R_OUT
(MAX3221E/
MAX3223E)
Active
High-Z
Active
High-Z
Active
High-Z
R_OUT
R2OUTB
(MAX3243E) (MAX3243E)
High-Z
High-Z
Active
Active
Active
Active
Active
Active
Active
Active
Active
Active
Shutdown
0
1
(AutoShutdown)
0
1
0
No
High-Z
Active
Active
Active
1
No
High-Z High-Z
Active
Active
X = Don’t Care
+0.3V
R_IN
-0.3V
TO MAX32_ _E
POWER SUPPLY
30µs AND TRANSMITTERS
COUNTER INVALID
R
* TRANSMITTERS ARE DISABLED, REDUCING SUPPLY CURRENT TO 1µA IF
ALL RECEIVER INPUTS ARE BETWEEN +0.3V AND -0.3V FOR AT LEAST 30µs.
Figure 3a. MAX32_ _E Entering 1µA Supply Mode via
AutoShutdown
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 VCC, V- is pulled to ground, and the
transmitter outputs are high impedance. The time
required to exit shutdown is typically 100µs (Figure 5b).
Software-Controlled Shutdown
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.
+2.7V
TO MAX32_ _E
R_IN
30µs
POWER SUPPLY
COUNTER INVALID
-2.7V
R
*TRANSMITTERS ARE ENABLED IF:
ANY RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V.
ANY RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30µs.
Figure 3b. MAX32_ _E with Transmitters Enabled Using
AutoShutdown
±15kV ESD Protection
As with all Maxim devices, ESD-protection structures are
incorporated on all pins to protect against electrostatic
discharges encountered during handling and assembly.
The driver outputs and receiver inputs of the
MAX3221E/MAX3223E/MAX3243E have extra protection
against static electricity. Maxim’s engineers have devel-
oped state-of-the-art structures to protect these pins
against ESD of ±15kV without damage. The ESD struc-
tures withstand high ESD in all states: normal operation,
shutdown, and powered down. After an ESD event,
Maxim’s E versions keep working without latchup,
whereas competing RS-232 products can latch and
must be powered down to remove latchup. See Table 4.
Maxim Integrated
9
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