NUP4202W1

http://onsemi.com

4

D1

D2

Data Line

−VF

Power

Supply

Protected

Device

Looking at the figure above, it can be seen that when a

positive ESD condition occurs, diode D1 will be forward

biased while diode D2 will be forward biased when a

negative ESD condition occurs. For slower transient

conditions, this system may be approximated as follows:

For positive pulse conditions:

For negative pulse conditions:

ESD events can have rise times on the order of some

number of nanoseconds. Under these conditions, the effect

of parasitic inductance must be considered. A pictorial

representation of this is shown below.

D1

D2

Data Line

Power

Supply

Protected

Device

An approximation of the clamping voltage for these fast

transients would be:

For positive pulse conditions:

For negative pulse conditions:

As shown in the formulas, the clamping voltage (Vc) not

only depends on the Vf of the steering diodes but also on the

result in hundreds of volts appearing on the supply rail. This

endangers both the power supply and anything attached to

that rail. This highlights the importance of good board

layout. Taking care to minimize the effects of parasitic

inductance will provide significant benefits in transient

immunity.

Even with good board layout, some disadvantages are still

present when discrete diodes are used to suppress ESD

events across datalines and the supply rail. Discrete diodes

with good transient power capability will have larger die and

therefore higher capacitance. This capacitance becomes

problematic as transmission frequencies increase. Reducing

capacitance generally requires reducing die size. These

small die will have higher forward voltage characteristics at

typical ESD transient current levels. This voltage combined

with the smaller die can result in device failure.

The ON Semiconductor NUP4202W1 was developed to

overcome the disadvantages encountered when using

discrete diodes for ESD protection. This device integrates a

TVS diode within a network of steering diodes.

D1

D2

D3

D4

D5

D6

D7

D8

0

NUP4202W1 Equivalent Circuit

During an ESD condition, the ESD current will be driven

to ground through the TVS diode as shown below.

D1

D2

Data Line

Power

Supply

Protected

Device

The resulting clamping voltage on the protected IC will

be:

The clamping voltage of the TVS diode is provided in

Figure 4 and depends on the magnitude of the ESD current.

The steering diodes are fast switching devices with unique

forward voltage and low capacitance characteristics.