UC3525A and external frequency sync.

Hello,

i would like to synchronize an UC3525A with an external frequency going to µC.

Datasheet are miserable, and i don't know how to configure RT and CT in this case.
Is it Master Fosc (external) must be more that Slave Fosc (UC3525A)?
I have a Master Clock shifting: 20KHz<Fosc(Master)<50KHz
If someone have a solution, thanks by advance.

Nobody know?
regards.

POWERMAN said:

Hello,

i would like to synchronize an UC3525A with an external frequency going to µC.

Datasheet are miserable, and i don't know how to configure RT and CT in this case.
Is it Master Fosc (external) must be more that Slave Fosc (UC3525A)?
I have a Master Clock shifting: 20KHz<Fosc(Master)<50KHz
If someone have a solution, thanks by advance.

Click to expand...

It is true that there is no mention anywhere else except in the Features list. However, Texas Instruments have a large library of application notes. perhaps you may have to swim through their Library to have some definite info.

However, it appears that we have to design the local oscillator few cycles above the wanted freq and thereafter when you provide the sync clock , it will synchronize to that.

Instead,you may bring an external oscillator, connect it to number of switchers as external clock using individual buffer gates, and it might well serve your needs. it will also reduce individual oscillator related components from the part list.

I sarma,

thanks for reply, Unitrode (Texas now) had applications notes, but Texas is not Unitrode ten years ago... i have send few requests since 15 days no replies.
Today is very difficult to have informations, Texas is horrible for this particular case.

So,i have not found any applications notes in web for this particular question.
I have not well understand your explanation too, could you develop more please?

Regards

Sync the UC3525

It has been a long time…..Sync the UC3525.

If I remember right the sync pin should be at ground most of the time and sending it a TTL hi for a short time will reset the oscillator. Set the RC to free run slightly slower than your slowest frequency. Sorry I don’t remember what pulse length. I suggest using a pulse generator to inject a signal into the UC3525. Play with pulse width and frequency until it works well.

I have much more experience with syncing the UC3842 and family that does not have a sync pin. There are application notes on that.

ronsimpson said:

It has been a long time…..Sync the UC3525.

If I remember right the sync pin should be at ground most of the time and sending it a TTL hi for a short time will reset the oscillator. Set the RC to free run slightly slower than your slowest frequency. Sorry I don’t remember what pulse length. I suggest using a pulse generator to inject a signal into the UC3525. Play with pulse width and frequency until it works well.

I have much more experience with syncing the UC3842 and family that does not have a sync pin. There are application notes on that.

Click to expand...

Thanks Ron, is it possible to get more light on the sync mode working for devices like UC352x from some of your engineers in the field. this is a funny situation that there is no much info available openly.

ronsimpson said:

It has been a long time…..Sync the UC3525.

If I remember right the sync pin should be at ground most of the time and sending it a TTL hi for a short time will reset the oscillator. Set the RC to free run slightly slower than your slowest frequency. Sorry I don’t remember what pulse length. I suggest using a pulse generator to inject a signal into the UC3525. Play with pulse width and frequency until it works well.

I have much more experience with syncing the UC3842 and family that does not have a sync pin. There are application notes on that.

Click to expand...

Thanks for this reply, you confirm my last hypothesis after looking about oscillator schematic of the datasheet.
UC3525AN is a very efficient circuit for push-pull, to this day.
I use already UC3842 for flyback and forward, good circuit too.

I'm trying with 1µs width (max clock width in datasheet).
I'll give you my final results after tests.
My application is for drive power ultrasonics transducers and i must shifting frequency for find ringing and so the best efficiency.

Thanks to all again for your help.
Regards.

POWERMAN said:

Thanks for this reply, you confirm my last hypothesis after looking about oscillator schematic of the datasheet.
UC3525AN is a very efficient circuit for push-pull, to this day.
I use already UC3842 for flyback and forward, good circuit too.

I'm trying with 1µs width (max clock width in datasheet).
I'll give you my final results after tests.
My application is for drive power ultrasonics transducers and i must shifting frequency for find ringing and so the best efficiency.

Thanks to all again for your help.
Regards.

Click to expand...

At last I have got some info, on 35C25 if not 3525.
Attached datasheet has small description on page 5of 8. Ronsimpson is correct that the chips' oscillator frequency should be slightly low.

Look for some XXX 3524. My feeling is that they are quite close. Just as an approach.

atferrari said:

Look for some XXX 3524. My feeling is that they are quite close. Just as an approach.

Click to expand...

Hi Atfarrari,
we tried like anything. no details of sync methods except the one i could find on 35c25 made by telcom