Question about SG3524

Tihomir Tunchev

Other Parts Discussed in Thread: SG3524

I am using SG3524 to control a half bridge inverter or a buck converter.

On Pin7 CT (saw-tooth signal), on the falling edge, I see a jitter of 1.5 uS max, even if there is no input signal at Pin2.

This is constant at any frequency.

I see no information on the specs about this problem. Is this the normal operation?

Thanks,

Tihomir

over 11 years ago

0 Ron Michallick over 11 years ago

TI__Guru**** 164926 points

Tihomir,

It is not normal. I checked CT signal with CT = 2nF, RT=2k, VCC =15V, Vref cap = 0.1uF.

7875.SG2524.TIF

Check the layout for the CT capacitor connection to DUT GND pin.

0 Tihomir Tunchev over 11 years ago in reply to Ron Michallick

Prodigy 105 points

Hello Ron,

I was using similar values: CT=1.5nF, RT=2.7k. I was planning to use a trim pot 100kHz to vary the frequency.

However, I tried with the same values as you suggested and the jitter is still the same.

0 Tihomir Tunchev over 11 years ago in reply to Tihomir Tunchev

Prodigy 105 points

The Vref Cap doesn't seem to change anything.

I built the simple circuit on a separate breadboard, just the IC with RT, CT, and Vref Cap to eliminate any other interference.

I also tried with a new IC, different power supply and I connected large DC caps near the power lines, the jitter is still there...

I am attaching my main schematic.

Thanks,

Tihomir

0 Tihomir Tunchev over 11 years ago in reply to Tihomir Tunchev

Prodigy 105 points

Hello Ron,

Following your diagram, I discovered that the signal looks much better if the triggering is by the Falling edge, but the jitter is transferred to the rising edge.

I think this is the normal behavior.

Thank you very much for taking the time to help with this issue.

Best,

Tihomir

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Question about SG3524