MAX3380E/MAX3381E
+2.35V to +5.5V, 1µA, 2Tx/2Rx RS-232 Transceivers
with ±15kV ESD-Protected I/O and Logic Pins
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to IEC 1000-4-2 are generally lower than 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 con-
nects the probe to the device before the probe is ener-
gized.
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. All pins require this protection 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
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 2 for required capacitor values. Do not use val-
ues smaller than those listed in Table 2. 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
C5 to maintain the proper ratios (C1 to the other capac-
itors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a large nominal value. The capacitor’s equiva-
lent series resistance (ESR) usually rises at low
temperatures and influences the amount of ripple on
V+ and V-.
Power-Supply Decoupling
In most circumstances, connect a 0.1µF capacitor from
V
CC
to GND. This capacitor is for noise reduction. If the
MAX3380E/MAX3381E are used in a data cable appli-
cation, add a 47µF capacitor from V
CC
to ground. The
47µF capacitor is used to ensure that the current need-
ed during power-up is supplied to the device. In appli-
cations that are sensitive to power-supply noise,
decouple V
CC
to ground with a capacitor of the same
value as charge-pump capacitor C1. Connect bypass
capacitors as close to the IC as possible.
Transmitter Outputs when Recovering
from 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 (one transmitter input is high, the other is low). Each
transmitter is loaded with 3kΩ in parallel with 1000pF.
The transmitter outputs display no ringing or undesir-
able transients as they come out of shutdown. Note that
the transmitters are enabled only when the magnitude
of V- exceeds approximately 3V.
High Data Rates
The MAX3380E/MAX3381E maintain the RS-232 ±5.0V
minimum transmitter output voltage even at high data
rates. Figure 8 shows a transmitter loopback test cir-
cuit. Figure 9 shows a loopback test result for the
MAX3380E at 460kbps with true RS-232 output voltage
levels (V
CC
= +4.2V). Figure 10 shows the same test
with RS-232-compatible levels (V
CC
= +2.5V). With
data rates as high as 460kbps, the MAX3380E is com-
patible with 2.5-Generation GSM standards.
