SRDA05-4(2007) データシートの表示（PDF） - Semtech Corporation

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SRDA05-4
(Rev.:2007)

RailClamp® Low Capacitance TVS Diode Array

Semtech Corporation 

SRDA05-4 and SRDA12-4

PROTECTION PRODUCTS

Applications Information (continued)

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

approximation, the clamping voltFage due to the charac-

teristics of the protection diodes is given by:

VPCIN= VDCCe+scVrFipt(ifoonr spositive duration pulses)

V = -V

C

F

(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:

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

V = V + V + L di /dt (for positive duration pulses)

C

CC

F

P ESD

(First Approximation)

V = -V - L di /dt

C

F G ESD

(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:

V = L di /dt = 1X10-9 (30 / 1X10-9) = 30V

P ESD

Example:

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

steering diodCeC and a series tracF e inductance of 10nH.

The clamping voltage seen by the protected IC for a

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

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

C

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

the high V of the discrete diode. It is not uncommon

for the V Fof discrete diodes to exceed the damage

thresholdF of the protected IC. This is due to the

relatively small junction area of typical discrete compo-

nents. 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

helps to mitigate the effects of parasitic inductance in

Figure 3 - Rail-To-Rail Protection Using

RailClamp TVS Arrays

© 2007 Semtech Corp.

6

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