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PI2002-EVAL1 User Guide Rev 1.0 Page 9 of 11

8.0 Input short circuit test

8.1 To emulate a real application, the BUS supplies for this

test should have a solid output source such as DC-DC

converter that supplies high current and can be

connected very close to the evaluation board to

reduce stray parasitic inductance. Or use the

prospective supply sources of the end application

where the PI2002 will be used.

8.2 Stray parasitic inductance in the circuit can contribute

to significant voltage transient conditions, particularly

when the MOSFETs are turned-off after a reverse

current fault has been detected. When a short is

applied at the output of the input power sources and

the evaluation board input (Vin), a large reverse

current is sourced from the evaluation board output

through the ORing MOSFETs. The reverse current in

the MOSFET may reach over 60 A in some conditions

before the MOSFETs are turned off. Such high current

conditions will store high energy even in a small

parasitic element, and can be represented as ½ Li2. A

1 nH parasitic inductance with 60 A reverse current

will generate 1.8 µJ. When the MOSFETs are turned

off, the stored energy will be released and will

produce a high negative voltage at D1 and high

positive voltage at D2. This event will create a high

voltage difference across the MOSFETs.

8.3 Apply a short at one of the inputs (Vin1 or Vin2).

The short can be applied electronically using a

MOSFET connected between Vin and Gnd or simply by

connecting Vin to Gnd. Then measure the response

time between when the short is applied and the

MOSFETs are disconnected (or turned off). An example

for PI2002 response time to an input short circuit is

shown in Figure 7.

Figure 7 – Plot of PI2002 response time to reverse current detection