How test a 16 pin PFC IC 28063D

[repair-it]

Can anyone tell me how I can test a 16 pin PFC IC 28063D out of circuit? I tried applying 12-14v to VCC but did not get a signal on either gate out pin. I read elsewhere for a different PFC IC that it requires 1+v on VSENSE at the same time to get a GATE signal. Just seeking the correct method.

[truclacicr]

https://www.ti.com/lit/ds/symlink/ucc28063.pdf

7.3.15.3 Open-Loop Protection

If the feedback loop is disconnected from the device, a 100-nA current source internal to the UCC28063 pulls the
VSENSE pin voltage towards ground. When VSENSE falls below 1.20 V, the device becomes disabled. When
disabled, the bias supply current decreases, both gate-drive outputs and COMP are actively pulled low, and a
soft-start condition is initiated. The device is re-enabled when VSENSE rises above 1.25 V. At that time, the gate
drive outputs will begin switching under soft-start PWM control.

If the feedback loop is disconnected from ground, the VSENSE voltage will be pulled high. When VSENSE rises
above the 2nd-level over-voltage protection threshold, both gate drive outputs are shut off and COMP is actively
pulled low. The device is re-enabled when VSENSE falls below the OV-clear threshold. The VSENSE input can
tolerate a limited amount of current into the device under abnormally high input voltage conditions. Refer to the
Absolute Maximum Ratings table near the beginning of this datasheet for details.

[repair-it]

Thank you for those details. I'm not sure what type of gate signal I should expect. All grounds are connected to a single connection which then goes to the IC ground pin. Applied 14v to VCC. When applying 3v to VSENSE on the original IC in question, I am getting either a spike-like signal or I get just a flat line DC voltage output. I had expected to see a pulsing square wave. On the replacement IC that I just received from Digikey, connected the same way, I'm only getting a flatline low DC voltage output on the gate. I'm just trying to determine what the gate output signal should look like. The IC was removed from a samsung power supply board after shorting the same mosfet twice, I suspect the PFC IC may have failed.

[truclacicr]

Use a pot to vary VSENSE from 1V to 1.5V, say. When the voltage passes through the hysteresis band (1.20V - 1.25V), the output should switch from off to on, or vice versa.

[repair-it]

Should I expect to see a wave pattern or just flatline DC voltage?

[truclacicr]

I'm not sure. I guess it would depend on whether the IC allows for a 100% duty cycle on the output, which I doubt.