MAX3224ECTP datasheet(14/21 Pages) MAXIM

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±15kV ESD-Protected, 1µA, 1Mbps 3.0V to 5.5V,

RS-232 Transceivers with AutoShutdown Plus

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 MAX3224E–MAX3227E,

MAX3244E/MAX3245E help you design equipment that

meets Level 4 (the highest level) of IEC 1000-4-2, with-

out 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 7a shows the IEC 1000-4-2 model and

Figure 7b shows the current waveform for the 8kV, IEC

1000-4-2, Level 4, ESD Contact-Discharge Method.

The Air-Gap Method 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

Capacitor Selection

The capacitor type used for C1–C4 is not critical for

proper operation; polarized or nonpolarized capacitors

can be used. The charge pump requires 0.1µF capaci-

tors for 3.3V operation. For other supply voltages, see

Table 3 for required capacitor values. Do not use val-

ues 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, C4,

and CBYPASS, 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

excessively with temperature. If in doubt, use capaci-

tors with a larger nominal value. The capacitor’s equiv-

alent series resistance (ESR), which usually rises at low

temperatures, influences the amount of ripple on V+

and V-.

Power-Supply Decoupling

In most circumstances, a 0.1µF VCC bypass capacitor

is adequate. In applications that are sensitive to power-

supply noise, use a capacitor of the same value as

charge-pump capacitor C1. Connect bypass capaci-

tors as close to the IC as possible.

Transmitter Outputs

when Exiting Shutdown

Figure 8 shows two transmitter outputs when exiting

shutdown mode. As they become active, the two trans-

mitter outputs are shown going to opposite RS-232 lev-

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

VCC

(V)

C2, C3, C4

(

µF)

3.0 to 3.6

0.22

3.15 to 3.6

0.1

C1, CBYPASS

(

µF)

0.22

0.1

4.5 to 5.5

0.33

3.0 to 5.5

0.047

0.22

Table 3. Required Minimum Capacitance

Values

μs/div

T1OUT

FORCEON = FORCEOFF

T2OUT

READY

5V/div

2V/div

5V/div

VCC = 3.3V

C1–C4 = 0.1

μF

Figure 8. Transmitter Outputs when Exiting Shutdown or

Powering Up

Maxim Integrated

MAX3224E/MAX3225E/

MAX3226E/MAX3227E/MAX3244E/MAX3245E

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