UC2525A: SYNC input Vs Output A or Output B

meng John

Part Number: UC2525A

Using an external input signal ( 187Khz) on sync (pin3) and get a about 740Khz signal from Out A and Out B at that time the Ct capacitor connected to PIN5 was removed. So are the output signals from out A (PIN11) and Out B (PIN14) correct ?

In addition, how to make the sync input signal equal to the output signals on OUT A and OUT B ?

Thanks!

over 2 years ago

0 Eric Reicher over 2 years ago

TI__Expert 7900 points

Hi John,

Why did you remove the CT capacitor? Usually the "base" frequency of the regulator is set by RT/CT, then the incoming SYNC frequency must be 15-20% higher than the base frequency. I would place RT, CT, and RD. Check the base frequency. Then apply the SYNC waveform at 15-20% higher than the base frequency.

Also, the SYNC amplitude must be higher than 2.8V, as shown in the datasheet.

Regards,

Eric

+1 meng John over 2 years ago in reply to Eric Reicher

Prodigy 145 points

Hi Eric,

Thanks for your rapidly responses!

The purpose removed the Ct capacitor is to avoid the conflict between incoming Sync frequency and "base" frequency by Rt and Ct oscillation that was my initial idea.

I hope to use an incoming 100Khz - 300khz Sync frequency to get the same frequency on Out A and Out B , So could how I set the base frequency？ that is 80Khz (assuming 20% minimum Sync frequency) , right ?

Thanks!

John

0 Eric Reicher over 2 years ago in reply to meng John

TI__Expert 7900 points

Yes, set the base frequency to 80 kHz.

The controller needs a base frequency because it may take several cycles to synchronize to the incoming clock.

Eric

0 meng John over 2 years ago in reply to Eric Reicher

Prodigy 145 points

Got it, thanks,

John

0 Eric Reicher over 2 years ago in reply to meng John

TI__Expert 7900 points

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UC2525A: SYNC input Vs Output A or Output B