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 resis-

tance. Its objective is to emulate the stress caused by

contact that occurs with handling and assembly during

manufacturing. Of course, all pins require this protec-

tion 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

Charge Pumps

The MAX3233E/MAX3235E do not require external

capacitors to operate their internal charge pumps.

The MAX3235E can be operated down to 3.0V by par-

alleling the internal C1 capacitor with an external 0.1µF.

When using an external capacitor across the C1 termi-

nals, check to confirm that the total supply voltage

measured from V+ to V- does not exceed the absolute

maximum voltage of 13V. With the external 0.1µF

capacitor added, the MAX3235E should not be used

with a supply greater than +3.9V.

Power-Supply Decoupling

adequate. Connect bypass capacitors as close to the

IC as possible.

Transmitter Outputs

when Exiting 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

levels (one transmitter input is high, the other is low).

±15kV ESD-Protected, 1µA, 250kbps, 3.3V/5V, Dual

RS-232 Transceivers with Internal Capacitors

10

______________________________________________________________________________________

tr = 0.7ns to 1ns

30ns

60ns

t

100%

90%

10%

I

Figure 6b. IEC 1000-4-2 ESD Generator Current Waveform

10

µs/div

T1OUT

T2OUT

5V/div

0

2V/div

0

10V/div

0

FORCEON = FORCEOFF

Figure 7. Transmitter Outputs when Exiting Shutdown or

Powering Up

MAX3233E

MAX3235E

5k

Ω

R_ IN

R_ OUT

FORCEON

FORCEOFF

T_ OUT

T_ IN

GND

1000pF

Figure 8. Loopback Test Circuit