Picor Corporation •
picorpower.com
PI2127-EVAL1 User Guide
Rev. 1.0
Page
6 of 9
4.10.
D2 should be on. This is due to a reverse
voltage fault condition caused by the bus
voltage being high with respect to the input
voltage (Vin2+).
4.11.
Enable (turn on) PS2 output.
4.12.
Verify that both PS1 and PS2 are sharing load
current evenly by looking at the supply current.
Power supplies output
may need adjustment to
set current sharing between the supplies.
4.13.
Disable (turn off) PS1, PS2, and PS3 outputs.
4.14.
Enable (turn on) PS2 output then Enable and
PS3 outputs.
4.15.
Verify that the electronic load voltage reading is
few millivolts below 48V. This verifies that the
PI2127-01-LGIZ
internal
MOSFET
is
in
conduction mode.
4.16.
D2 should be off. This verifies that there is no
fault condition.
4.17.
Verify that Vin1+ is low. This verifies that the
PI2127 (U1) internal FET is off.
4.18.
D1 should be on. This is due to a reverse
voltage fault condition caused by the bus
voltage being high with respect to the input
voltage (Vin1+).
Note:
When the PI2127 internal MOSFET is in the on
state, it will not turn off unless a reverse current
greater than 0.75A is sensed in the MOSFET.
When both power supplies are enabled and both
PI2127 MOSFETs are in R
DS(on)
; if one of the sources
(Power supplies) removed or disabled both PI2127
stay on unless the disabled power supply sources
current greater than 0.75A when turned off.
5.
Internal MOSFET R
DS(on)
Measurement:
5.1.
The internal MOSFET R
DS(on)
can be measured
with a voltmeter between the S1 and D1 Kelvin
connection for U1 and between the S2 and D2
Kelvin connection for U2. The potential
between S1 and D1 is the voltage drop across
the internal MOSFET and:
Where:
:
Voltage drop across the internal
MOSFET
:
Input current.
Note: The R
DS(on)
value is temperature dependent and the
junction
temperature
increases
directly
proportional to power dissipation.
6.
Input short circuit test:
PI2127 has a very fast response (80ns) to a reverse current
(Input short) fault condition. Measuring a short period
event requires attention to the test set-up. Before
proceeding, consider the following:
6.1.
To emulate a real application, the BUS supplies
for this test should have a solid output source
such as a 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 PI2127
will be used. Typical bench power supplies have
slow response to output load change. In this test
when the power supply output is shorted and
then released, the bench power supply may
produce high output voltage with high current
capability that may damage the device under
test.
6.2.
Do not install Input capacitors (C1 and/or C2) in
this test.
6.3.
Output capacitor (C5) should be installed.
6.4.
Place the scope probes very close to the PI2127 S
and D pins to measure Vin and Vout, and make
sure that the scope ground leads are very short.
You may use a close by ground pad for the scope
probe return, such as C1, C2, C3 and C4 return
pads.
6.5.
Apply a short at one of the inputs (Vin1+ or
Vin2+) when both SIP’s (U1 and U2) are on, PS1
and PS2 are enabled. The short can be applied
electronically using a MOSFET connected
between Vin+ and Vin- or simply by connecting
Vin+ to Vin-. Then measure the response time
between when the short is applied and the
PI2127 internal MOSFET is disconnected (or
turned off). An example for the PI2127 response
time to an input short circuit is shown in Figure
4.
