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SRDA12-4.TB Datasheet(PDF) 6 Page - Semtech Corporation |
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SRDA12-4.TB Datasheet(HTML) 6 Page - Semtech Corporation |
6 / 10 page 6 ã 2000 Semtech Corp. www.semtech.com PROTECTION PRODUCTS PROTECTION PRODUCTS SRDA3.3-4 THRU SRDA12-4 PIN Descriptions Figure 1 - Rail-To-Rail Protection Topology (First Approximation) Figure 2 - The Effects of Parasitic Inductance When Using Discrete Components to Implement Rail-To-Rail Protection Figure 3 - Rail-To-Rail Protection Using RailClamp TVS Arrays Applications Information (continued) approximation, the clamping voltage due to the charac- teristics of the protection diodes is given by: V C = V CC + V F (for positive duration pulses) V C = -V 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: V C = V CC + V F + L P di ESD /dt (for positive duration pulses) V C = -V F - L G di ESD /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: V = L P di ESD /dt = 1X10-9 (30 / 1X10-9) = 30V Example: Consider a V CC = 5V, a typical V F 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: V C = 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 the high V F of the discrete diode. It is not uncommon for the V F of discrete diodes to exceed the damage threshold 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. The RailClamp is designed to overcome the inherent disadvantages of using discrete signal diodes for ESD suppression. The RailClamps integrated TVS diode helps to mitigate the effects of parasitic inductance in the power supply connection. During an ESD event, |
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