±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,
Up to 1Mbps, True RS-232 Transceivers
ESD protection can be tested in various ways; the
transmitter outputs and receiver inputs for the
MAX3222E/MAX3232E/MAX3237E/MAX3241E are
characterized for protection to the following limits:
• ±15kV using the Human Body Model
• ±8kV using the Contact Discharge method specified
in IEC 1000-4-2
V
CC
• ±15kV using IEC 1000-4-2’s Air-Gap Discharge
method
ESD Test Conditions
ESD performance depends on a variety of conditions.
Contact Maxim for a reliability report that documents
test setup, test methodology, and test results.
Human Body Model
Figure 4a shows the Human Body Model, and Figure
4b shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
est, which is then discharged into the test device
through a 1.5kΩ 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 integrated circuits. The MAX3222E/MAX3232E/
MAX3237E/MAX3241E help you design 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 higher peak
current in IEC 1000-4-2 because series resistance is
lower in the IEC 1000-4-2 model. Hence, the ESD with-
stand voltage measured to IEC 1000-4-2 is generally
lower than that measured using the Human Body
Model. Figure 5a shows the IEC 1000-4-2 model, and
Figure 5b shows the current waveform for the ±8kV IEC
1000-4-2 Level 4 ESD Contact Discharge test.
The Air-Gap Discharge test involves approaching the
device with a charged probe. The Contact Discharge
MAX3222E/MAX3232E/MAX3237E/MAX3241E
V
CC
PROTECTION
DIODE
Rx
PREVIOUS
RS-232
5kΩ
UART
Tx
GND
SHDN = GND
a)
OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM
ACTIVE RECEIVER OUTPUT IN SHUTDOWN.
V
CC
TO
µP
LOGIC
TRANSITION
DETECTOR
MAX3237E/MAX3241E
R1OUTB
V
CC
PROTECTION
DIODE
Rx
R1OUT
THREE-STATED
EN = V
CC
5kΩ
R1IN
5V/div
0
SHDN
T2OUT
UART
Tx
GND
T1IN
SHDN = GND
T1OUT
2V/div
0
b)
NEW MAX3237E/MAX3241E: EN SHUTS DOWN RECEIVER OUTPUTS
(EXCEPT FOR B OUTPUTS), SO NO CURRENT FLOWS TO UART IN SHUTDOWN.
B OUTPUTS INDICATE RECEIVER ACTIVITY DURING SHUTDOWN WITH EN HIGH.
V
CC
= 3.3V
C1–C4 = 0.1µF
40µs/div
T1OUT
Figure 2. Detection of RS-232 Activity when the UART and
Interface are Shut Down; Comparison of MAX3237E/MAX3241E
(b) with Previous Transceivers (a)
Figure 3. Transmitter Outputs Recovering from Shutdown or
Powering Up
_______________________________________________________________________________________
9
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