MAX3238E/MAX3248E
10 ______________________________________________________________________________________
Therefore, the Machine Model is less relevant to the I/O
ports than the Human Body Model and IEC 1000-4-2.
Applications Information
Capacitor Selection
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, see
Table 3 for required capacitor values. Do not use val-
ues 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, C4,
and C
BYPASS
to maintain the proper ratios (C1 to the
other capacitors).
Power-Supply Decoupling
In most applications, decouple V
CC
to ground with a
0.1µF capacitor. Further increasing this capacitor value
reduces power-supply ripple and enhances noise mar-
gin. Connect the bypass capacitor as close to the IC as
possible.
Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform
+3.0V to +5.5V, 10nA, 250kbps RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
V
CC
(V)
C2, C3, C4
(µF)
3.0 to 3.6 0.22
C1, C
BYPASS
(µF)
0.22
4.5 to 5.5 0.33
3.0 to 5.5 1
0.047
0.22
Table 3. Required Minimum Capacitance
Values
3.15 to 3.6 0.10.1
