2.5V, ±15kV ESD-Protected RS-232

Transceivers for PDAs and Cell Phones

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7

shutdown is typically 30µs, as shown in Figure 2.

In shutdown mode, the receiver outputs are high imped-

ance (Table 1).

Unlike other RS-232 interface devices where the receiver

olds for the transmitter inputs. This feature allows a

great deal of flexibility in interfacing to many different

types of systems with different logic levels. Connect

this input to the host logic supply (1.8V

Also see the Typical PDA/Cell-Phone Application sec-

tion.

±15kV ESD Protection

As with all Maxim devices, ESD-protection structures are

incorporated on all pins to protect against ESDs encoun-

tered during handling and assembly. The MAX3388E/

MAX3389E’s driver outputs, receiver inputs, the hand-

shaking input LIN, and the switch terminal SWIN have

extra protection against static electricity. Maxim has

developed state-of-the-art structures to protect these pins

against an ESD of ±15kV without damage. The ESD

structures withstand high ESD in all states: normal opera-

tion, shutdown, and powered down. After an ESD event,

Maxim’s “E” version devices keep working without

latchup, whereas competing RS-232 products can latch

and must be powered down to remove latchup. ESD pro-

tection can be tested in various ways. The transmitter out-

puts and receiver inputs of this product family are

characterized for protection to the following limits:

1) ±15kV using the Human Body Model

2) ±8kV using the Contact Discharge method specified

in IEC 1000-4-2

3) ±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, methodology, and results.

Human Body Model

Figure 3a shows the Human Body Model, and Figure 3b

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 interest,

which is then discharged into the test device through a

1.5k

Ω resistor.

IEC 1000-4-2

The IEC 1000-4-2 standard covers ESD testing and

performance of finished equipment; it does not specifi-

cally refer to ICs. The MAX3388E/MAX3389E helps 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 4a shows the IEC 1000-4-2 model, and

Figure 4b shows the current waveform for the ±8kV IEC

1000-4-2 Level 4 ESD Contact Discharge test.

CHARGE-CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

Cs

100pF

1M

Ω

1500

Ω

HIGH-

VOLTAGE

DC

SOURCE

DEVICE

UNDER

TEST

Figure 3a. Human Body ESD Test Model

90%

36.8%

TIME

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

Ir

10%

0

0

AMPERES

Figure 3b. Human Body Current Waveform