that measured using the Human Body Model. Figure 6a
shows the IEC 1000-4-2 model, and Figure 6b shows the
current waveform for the ±8kV, IEC 1000-4-2, Level 4,
ESD contact-discharge test.
The air-gap test involves approaching the device with a
charged probe. The contact-discharge method connects
the probe to the device before the probe is energized.
Machine Model
The Machine Model for ESD tests all pins using a
200pF storage capacitor and zero discharge resis-
tance. Its objective is to emulate the stress caused by
contact that occurs with handling and assembly during
manufacturing. Of course, all pins require this protec-
tion during manufacturing, not just RS-232 inputs and
outputs. Therefore, after PC board assembly, the
Machine Model is less relevant to I/O ports.
__________Applications Information
Charge Pumps
The MAX3233E/MAX3235E do not require external
capacitors to operate their internal charge pumps.
The MAX3235E can be operated down to 3.0V by par-
alleling the internal C1 capacitor with an external 0.1µF.
When using an external capacitor across the C1 termi-
nals, check to confirm that the total supply voltage
measured from V+ to V- does not exceed the absolute
maximum voltage of 13V. With the external 0.1µF
capacitor added, the MAX3235E should not be used
with a supply greater than +3.9V.
Power-Supply Decoupling
In most applications, a 0.1µF V
CC
bypass capacitor is
adequate. 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
levels (one transmitter input is high, the other is low).
MAX3233E/MAX3235E
±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual
RS-232 Transceivers with Internal Capacitors
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