±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
The major difference between tests done using the
Human Body Model and IEC1000-4-2 is higher peak
current in IEC1000-4-2, because series resistance is
lower in the IEC1000-4-2 model. Hence, the ESD with-
stand voltage measured to IEC1000-4-2 is generally
lower than that measured using the Human Body
Model. Figure 7a shows the IEEE1000-4-2 model and
Figure 7b shows the current waveform for the ±8kV
IEC1000-4-2 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.
MAX3221E/MAX3223E/MAX3243E
Table 3. Required Capacitor Values
V
CC
(V)
3.0 to 3.6
3.15 to 3.6
4.5 to 5.5
3.0 to 5.5
C1, C
BYPASS
(µF)
0.22
0.1
0.047
0.22
C2, C3, C4
(µF)
0.22
0.1
0.33
1
Table 4. Logic Family Compatibility with
Various Supply Voltages
SYSTEM
POWER-
SUPPLY
VOLTAGE
(V)
3.3
5
V
CC
SUPPLY
VOLTAGE
(V)
3.3
5
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.
COMPATIBILITY
Compatible with all CMOS
families.
Compatible with all TTL and
CMOS-logic families.
Compatible with ACT and
HCT CMOS, and with TTL.
Incompatible with AC, HC,
or CD4000 CMOS.
___________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, refer to 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 exces-
sively with temperature. If in doubt, use capacitors with a
larger nominal value. The capacitor’s equivalent series
resistance (ESR) usually rises at low temperatures and
influences the amount of ripple on V+ and V-.
5
3.3
5V/div
FORCEON =
FORCEOFF
T2OUT
2V/div
V
CC
= 3.3V
C1–C4 = 0.1µF
40µs/div
T1OUT
Figure 8. Transmitter Outputs Exiting Shutdown or Powering Up
Transmitter Outputs
when Exiting Shutdown
Figure 8 shows two transmitter outputs when exiting
shut down mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232 lev-
els (one transmitter output is high, the other is low).
Each transmitter is loaded with 3kΩ in parallel with
1000pF. The transmitter outputs display no ringing or
undesirable transients as they come out of shutdown,
and are enabled only when the magnitude of V-
exceeds approximately -3V.
11
Power-Supply Decoupling
In most circumstances, a 0.1µF V
CC
bypass capacitor is
adequate. In applications that are sensitive to power-
supply noise, use a capacitor of the same value as the
charge-pump capacitor C1. Connect bypass capacitors
as close to the IC as possible.
______________________________________________________________________________________
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
