DP83847 datasheet(25/60 Pages) NSC

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3.6 ESD Protection

Typically, ESD precautions are predominantly in effect

when handling the devices or board before being installed

in a system. In those cases, strict handling procedures can

be implemented during the manufacturing process to

greatly reduce the occurrences of catastrophic ESD

events. After the system is assembled, internal compo-

nents are usually relatively immune from ESD events.

In the case of an installed Ethernet system however, the

network interface pins are still susceptible to external ESD

events. For example, a category 5 cable being dragged

across a carpet has the potential of developing a charge

well above the typical ESD rating of a semiconductor

device.

For applications where high reliability is required, it is rec-

ommended that additional ESD protection diodes be added

as shown below. There are numerous dual series con-

nected diode pairs that are available specifically for ESD

protection. The level of protection will vary dependent upon

the diode ratings. The primary parameter that affects the

level of ESD protection is peak forward surge current. Typi-

cal specifications for diodes intended for ESD protection

range from 500mA (Motorola BAV99LT1 single pair diodes)

to 12A (STM DA108S1 Quad pair array). The user should

also select diodes with low input capacitance to minimize

the effect on system performance.

Since performance is dependent upon components used,

board impedance characteristics, and layout, the circuit

should be completely tested to ensure performance to the

required levels.

Figure 9. Typical DP83847 Network Interface with additional ESD protection

RJ-45

DP83847 10/100

TX±

RX±

Vcc

PIN 1

PIN 2

PIN 3

PIN 6

DIODES PLACED

ON THE DEVICE

SIDE OF THE

ISOLATION

TRANSFORMER

3.3V Vcc

Vcc

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