UCC2894: Output no signal

Hi,

Pin 8 (Rslope), we never ground this pin, you may try to add 100k-ohm resistor from this pin to GND.

Pin 2 (Rdel), its value is too small, I suggest to change it to be about 20k-ohm

Can you provide the waveforms: VDD (pin 16), SS (pin 10), OUT (pin 13), FB (pin 9), and VREF (pin 4), during power on?

Basically, when VDD reaches above 13.2V, soft start should start to rise, and OUT won't have the pulses, until SS reaches above 1.25V. Before the SS reaches > 1.25V you won't see OUT pulses. 

 Hi,

Please provide the waveform during power on SS OUT VDD VREF, to show SS start from 0 to 5V and the other three how they follow SS during SS rise from 0 to 5V.

Hi,

Can you provide the ucc2894 IC top surface marking? Also where did you get the IC sample? This can help if your sample is a correct one to use.

Can you try a different unit?

If you still cannot see the pulses from OUT you need to initiate a return process to request FA analysis since OUT should have pulses when SS > 1.25V.

Hi, 

page 4 of the datasheet shows four conditions can discharge the SS. You mentioned three and the fourth is Vdd. If they all are good then please ask your vendor or your ti local contact to start a FA process.