Technical Problem with the UCC2894

Daniel Gerber

Prodigy 10 points

Other Parts Discussed in Thread: UCC2894

Hello,

I am trying to get the UCC2894 working in standing alone operation.

The IC gets his 13,5V and he supplies Vref = 5V but the Softstart doesn´t start.

In my opinion I have a problem with the lineover- and undervoltage function.

Is it right that the overvoltagesignal has to be under 1,27V and the undervoltagesignal

has to be over 1,27V.

Thanks for answering.

Daniel

over 14 years ago

0 Hong Huang over 14 years ago

TI__Guru 73725 points

Yes, LineOV has to be less than 1.27V and LineUV has to be greater than 1.27V, together with VDD > 13.2V and Vref =5V, these are the conditions to have soft start begin.

0 Daniel Gerber83554 over 14 years ago in reply to Hong Huang

Prodigy 40 points

Thanks Hong,

now i have a pwm signal at OUT and AUX but with changing RON I can´t change the time of my out-signal.

ROFF changes the length of the AUX signal and so does RON too. What is wrong?

Is it possible to get an oscillator frequency of about 30kHz?

Thanks for answering.

Daniel

0 Hong Huang over 14 years ago in reply to Daniel Gerber83554

TI__Guru 73725 points

It looks 30kHz is achieavable based on the datasheet.

RON and ROFF are designed for DMAX and switching frequency, as shown in the datasheet page 8, equations (1) to (5).

The dirve signal duty cycle is controlled by FB-pin which effective control range is 2.5V to 4.5V.

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Technical Problem with the UCC2894