Vicor PI2121-EVAL1 Full-Function Active ORing Evaluation Board - Manual (Page 8)

Picor Corporation • www.picorpower.com PI2121-EVAL1 User Guide Rev 1.1 Page 8 of 12
6.8 Verify that electronic load voltage drops to a diode
drop below PS2. This verifies that the SiP2 internal
FET is off due to the Master (SiP1) not being on.
6.9 Enable (turn on) PS1 output:
6.10 Verify that the electronic load input voltage
reading is a few millivolts below 3.3 V and PS1 and
PS2 are sharing the load current evenly. This
verifies that both internal MOSFET's of SiP1 and
SiP2 are in conduction mode.
7.0 Input short circuit test
7.1 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 PI2121 will be used.
7.2 Stray parasitic inductance in the circuit can
contribute to significant voltage transient
conditions, particularly when the internal MOSFET
is 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
internal MOSFET. The reverse current in the
MOSFET may reach over 60 A in some conditions
before the MOSFET is turned off. Such high
current conditions will store high energy even in a
small parasitic element, and can be represented as
. A 1 nH parasitic inductance with 60 A reverse
current will generate 1.8 µJ. When the MOSFET is
turned off, the stored energy will be released and
will produce a high negative voltage at the MOSFET
source and high positive voltage at the MOSFET
drain. This event will create a high voltage
difference across the drain and source of the
MOSFET.
7.3 Apply a short at one of the inputs (Vin1 or Vin2)
when the evaluation board is configured with both
SiP's (SiP1 and SiP2) in master mode. 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 SiP internal MOSFET is disconnected (or
turned off). An example for PI2121 response time
to an input short circuit is shown in Figure 6.
Figure 6 – Plot of PI2121 response time to reverse current detection
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