MAX13223E Datasheet, PDF (9/11 Pages) Maxim Integrated Products – ±70V Fault-Protected, 3.0V to 5.5V, 2Tx/2Rx RS-232 Transceiver

±70V Fault-Protected, 3.0V to 5.5V,
2Tx/2Rx RS-232 Transceiver
Table 2. AutoShutdown Control
FORCEOFF
0
0
1
1
1
1
X = Don’t Care.
INPUTS
FORCEON
VALID RECEIVER INPUT
LEVEL
X
No
X
Yes
0
No
0
Yes
1
No
1
Yes
INVALID
OUTPUT
0
1
0
1
0
1
OUTPUTS
OPERATION MODE
Shutdown (Forced Off)
Shutdown (Forced Off)
Shutdown (AutoShutdown)
Active (AutoShutdown)
Active (Forced On)
Active (Forced On)
T_OUT
High-Z
High-Z
High-Z
Active
Active
Active
Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; either polarized or nonpolarized
capacitors may be used. The charge pump requires
0.1µF capacitors for 3.3V operation. For other supply
voltages, see Table 3 for required capacitor values. Do
not use values smaller than those listed in Table 3.
Increasing the capacitor values (e.g., by a factor of 2)
reduces ripple on the transmitter outputs and slightly
reduces power consumption. C2, C3, and C4 can be
increased without changing C1’s value. However, do
not increase C1 without also increasing the values
of C2, C3, and C4 to maintain the proper ratios (C1
to the other capacitors). When using the minimum
required capacitor values, make sure the capacitor
value does not degrade excessively with temperature.
If in doubt, use capacitors with a larger nominal value.
The capacitor’s equivalent series resistance (ESR) usu-
ally rises at low temperatures and influences the
amount of ripple on V+ and V-.
Table 3. Required Capacitor Values
V_CC (V)
3.0 to 3.6
4.5 to 5.5
C1, C_BYPASS (µF)
0.1
0.047
C2, C3 (µF)
0.1
0.33
C4 (µF)
1
1
Power-Supply Decoupling
In most circumstances, a 0.1µF V_CC bypass capacitor is
adequate. In applications that are sensitive to power-sup-
ply noise, decouple V_CC to ground with a capacitor of the
same value as the charge-pump capacitor C1. Connect
bypass capacitors as close to the IC as possible.
Transmitter Outputs when
Exiting Shutdown
Figure 7 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232 lev-
els. Each transmitter is loaded with 3kΩ in parallel with
2500pF. The transmitter outputs display no ringing or
undesirable transients as they come out of shutdown.
Note that the transmitters are enabled only when the
magnitude of V- exceeds approximately 3V.
5V/div
FORCEON =
FORCEOFF
T2OUT
2V/div
V_CC = +3.3V
C1–C4 = 0.1µF
40µs/div
T1OUT
Figure 7. Transmitter Outputs when Exiting Shutdown or
Powering Up
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