±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,

Up to 1Mbps, True RS-232 Transceivers

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9

MAX3222E/MAX3232E/MAX3237E/MAX3241E have

extra protection against static electricity. Maxim’s engi-

neers have developed state-of-the-art structures to pro-

tect these pins against ESD of ±15kV without damage.

The ESD structures withstand high ESD in all states:

normal operation, shutdown, and powered down. After

an ESD event, Maxim’s E versions keep working without

latchup, whereas competing RS-232 products can

latch and must be powered down to remove latchup.

Furthermore, the MAX3237E logic I/O pins also have

±15kV ESD protection. Protecting the logic I/O pins to

±15kV makes the MAX3237E ideal for data cable appli-

cations.

ESD protection can be tested in various ways; the

transmitter outputs and receiver inputs for the

MAX3222E/MAX3232E/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

•

±15kV using IEC 1000-4-2’s Air-Gap Discharge

method

For the MAX3237E, all logic and RS-232 I/O pins are

characterized for protection to ±15kV per the Human

Body Model.

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 1.5k

Ω resistor.

T1OUT

R1OUTB

Tx

5k

UART

T1IN

LOGIC

TRANSITION

DETECTOR

R1IN

R1OUT

THREE-STATED

SHDN = GND

TO

µP

Rx

PREVIOUS

RS-232

Tx

UART

PROTECTION

DIODE

PROTECTION

DIODE

SHDN = GND

GND

Rx

5k

a) OLDER RS-232: POWERED-DOWN UART DRAWS CURRENT FROM

ACTIVE RECEIVER OUTPUT IN SHUTDOWN.

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.

GND

MAX3237E/MAX3241E

Figure 2. Detection of RS-232 Activity when the UART and

Interface are Shut Down; Comparison of MAX3237E/

MAX3241E (b) with Previous Transceivers (a)

40

µs/div

SHDN

T2OUT

T1OUT

5V/div

0

2V/div

0

C1–C4 = 0.1

µF

Figure 3. Transmitter Outputs Recovering from Shutdown or

Powering Up