M
±15kV ESD-Protected +2.5V to +5.5V
RS-232 Transceivers in UCSP
_______________________________________________________________________________________
9
which is then discharged into the test device through a
1.5k
resistor.
IEC 1000-4-2
The IEC 1000-4-2 standard covers ESD testing and per-
formance of finished equipment. It does not specifically
refer to ICs. The MAX3230E/MAX3231E aid in designing
equipment that meets Level 4 (the highest level) of IEC
1000-4-2, without the need for additional ESD-protection
components.
The major difference between tests done using the
Human Body Model and IEC 1000-4-2 is a higher peak
current in IEC 1000-4-2, because series resistance is
lower in the IEC 1000-4-2 model. Hence, the ESD with-
stands voltage measured to IEC 1000-4-2 and is gener-
ally 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 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 resistance. Its
objective is to emulate the stress caused by contact that
occurs with handling and assembly during manufactur-
ing. Of course, 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; either polarized or nonpolarized
capacitors can be used. However, ceramic chip capaci-
tors with an X7R or X5R dielectric work best. The charge
pump requires 0.1μF capacitors for 3.3V operation. For
other supply voltages, see
Table 3
for required capaci-
tor values. Do not use values smaller than those listed in
Table 3
. Increasing the capacitor values (e.g., by a fac-
tor of 2) reduces ripple on the transmitter outputs and
slightly reduces power consumption. C2, C3, and C4
can be increased without changing the vaue of C1.
Caution:
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 exces-
sively with temperature. If in doubt, use capacitors with
Figure 3. AutoShutdown Trip Levels
V-
V
CC
0
V+
0
V
CC
t
INVL
t
WU
INVALID
REGION
RECEIVER
INPUT
VOLTAGE
(V)
INVALID
OUTPUT
(V)
t
INVH
TRANSMITTERS ENABLED, INVALID HIGH
R
AutoShutdown, TRANSMITTERS DISABLED,
1
μ
A SUPPLY CURRENT, INVALID LOW
TRANSMITTERS ENABLED, INVALID HIGH
a)
b)
-2.7V
-0.3V
+2.7V
+0.3V
0
INDETERMINATE
INDETERMINATE
Figure 4. AutoShutdown with Initial Turn-On to Wake Up a
Mouse or Another System
FORCEON
MASTER SHDN LINE
0.1
μ
F
1M
FORCEOFF
MAX3230E
MAX3231E
POWER-
MANAGEMENT
UNIT