SRV05-4(2004) データシートの表示（PDF） - Semtech Corporation

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SRV05-4
(Rev.:2004)

RailClamp® Low Capacitance TVS Diode Array

Semtech Corporation 

SRV05-4

PROTECTION PRODUCTS

Applications Information (continued)

the reference voltage plus the VF drop of the diode.

For negative events, the bottom diode will be biased

when the voltage exceeds the VF of the diode. At first

approximation, the clamping voltage due to the charac-

teristics of the protection diodes is given by:

PIN Descriptions

VC = VCC + VF (for positive duration pulses)

VC = -VF

(for negative duration pulses)

However, for fast rise time transient events, the

effects of parasitic inductance must also be consid-

ered as shown in Figure 2. Therefore, the actual

clamping voltage seen by the protected circuit will be:

VC = VCC + VF + LP diESD/dt (for positive duration pulses)

VC = -VF - LG diESD/dt

(for negative duration pulses)

ESD current reaches a peak amplitude of 30A in 1ns

for a level 4 ESD contact discharge per IEC 61000-4-2.

Therefore, the voltage overshoot due to 1nH of series

inductance is:

Figure 1 - “Rail-To-Rail” Protection Topology

(First Approximation)

V = LP diESD/dt = 1X10-9 (30 / 1X10-9) = 30V

Example:

Consider a VCC = 5V, a typical VF of 30V (at 30A) for the

steering diode and a series trace inductance of 10nH.

The clamping voltage seen by the protected IC for a

positive 8kV (30A) ESD pulse will be:

VC = 5V + 30V + (10nH X 30V/nH) = 335V

This does not take into account that the ESD current is

directed into the supply rail, potentially damaging any

components that are attached to that rail. Also note

that it is not uncommon for the VF of discrete diodes to

exceed the damage threshold of the protected IC. This

is due to the relatively small junction area of typical

discrete components. It is also possible that the

power dissipation capability of the discrete diode will

be exceeded, thus destroying the device.

Figure 2 - The Effects of Parasitic Inductance

When Using Discrete Components to Implement

Rail-To-Rail Protection

The RailClamp is designed to overcome the inherent

disadvantages of using discrete signal diodes for ESD

suppression. The RailClamp’s integrated TVS diode

Figure 3 - Rail-To-Rail Protection Using

RailClamp TVS Arrays

 2004 Semtech Corp.

6

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