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LTC6992 TimerBlox, jitter at low duty cycles

Folks,

Got an LTC6992 in the -3 version which goes from 0% to 95% duty cycle, controlling a fairly massive PWM stage. It lives inside a (stable) PID loop and works ok except at very low duty cycles under 2%. There is breaks into a jitter and because I am driving big capacitive loads that results in tons of wasted power. Also, it quite abruptly turns off at a fraction of a percent instead of gracefully going towards 0%.

I've babied the device quite well and all the signals look clean, including on the very sensitive SET pin. In case stuff gets into the die I have tried shielding the whole stage and even that changed nothing.

Anyone had that happen and knows a fix?

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg
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Usually noise in the Vcc supply, or inherient in the device operation. Does it do it on a seperate proto board?

I had a IRF 1/2 cycle PFC part that was noisy, tuff to decouple. A compatible TI part was well behaved.

Cheers

Reply to
Martin Riddle

Den fredag den 30. januar 2015 kl. 00.52.08 UTC+1 skrev Joerg:

some RC+diode concoction to "subtract" some duty cycle? so it'll do 0-90% cleanly?

-Lasse

Reply to
Lasse Langwadt Christensen

It did. Tried battery operation as well. VCC is very clean.

I don't think anyone make a compatible part to the LTC6992.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

92% would suffice. I thought about that but tossed the idea because it would be a major hack and re-layout. Then I might as well build my own PWM modulator. 
--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

That's on the data sheet, bottom of p 9. Some, not all, parts crash to

0% duty cycle at about 0.1 volt in.

The specs on that part are awful. Don't know how they managed to make it that bad.

--

John Larkin         Highland Technology, Inc 
picosecond timing   laser drivers and controllers 

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

Yes, but it doesn't say that it exhibits a tarantella dance around that point.

I really like LTC as a supplier but that part sure has me non-plussed. On the production run it's going to go bye-bye.

--
Regards, Joerg 

http://www.analogconsultants.com/
Reply to
Joerg

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