UCC2895: UCC2895 - minimum frequency

Rossano Valsecchi

Part Number: UCC2895

Hello

reading the data of the UCC2895 I saw that the minum frequency is about 90KHz (CTmax=880pF Rtmax=120K). In my application I need about 50KHz so I imposed Ct=2200pF and Rt=90Kohm. The prototype pass all the tests but I'm a little bit worried about long term reliability using components' values out of the range indicated in the data sheet.

Thank you

Rossano

over 5 years ago

0 Colin Gillmor over 5 years ago

TI__Mastermind 25570 points

Hello Rossano

The 880pF limit on Ct should be kept – if Ct is increased it increases the time needed to reset the CT pin at the end of each cycle and this reduces Dmax. The max limit on Rt was set by considerations of frequency accuracy.To get a 50kHz switching frequency they should use a 2200k resistor and 880pF capacitor. The frequency accuracy will be a little poorer but not greatly so.

You might consider using the UCC28951 which is specified for operation at 50kHz and includes SR drive outputs in addition to the primary switch outputs

Regards

Colin

0 Rossano Valsecchi over 5 years ago in reply to Colin Gillmor

Prodigy 240 points

Thank you. I'll adopt your suggestion

regards

rossano

0 Colin Gillmor over 5 years ago in reply to Rossano Valsecchi

TI__Mastermind 25570 points

Hi Rossano

I'm going to close this thread now but please feel free to contact us again if you have any further questions.

Regards

Colin

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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UCC2895: UCC2895 - minimum frequency