TPS548A28: Frequency variation of TPS548A28

Fred Cheng

Part Number: TPS548A28

Hi team,

as shown below, the frequency is out of spec,

I can't help but notice there's a equation of maximum frequency. And it's have two version which is limited by minimum on-time and minimum off time.

What's the difference between minimum on-time and off-time and why has this difference?

Does this have something to do with DCAP3?

Regards,

Fred

over 2 years ago

0 David_Daniels over 2 years ago

TI__Mastermind 20135 points

Maximum frequency equation is a limitation of the controllable on time, input voltage and output voltage. If regulating to 0.6V output at 16V with the max frequency setting, minimum on time is a controllable are a constraint. For off time, minimum input voltage, output voltage and switching frequency are a constraint. The device will regulate but the switching frequency will change.

The EC table specification is only valid for 1.2V output voltage.

Figure 8.4 to 8.6 https://www.ti.com/lit/ds/symlink/tps548a28.pdf%page=32 shows the switching frequency vs output voltage.

Check the output voltage of customer application and check against the graphs.

0 Fred Cheng over 2 years ago in reply to David_Daniels

TI__Expert 5150 points

Hi,

based on what I know, dcap3 is similar to COT , so the on-time is supposed to be constant, right?

BTW, I could not open the link you post above, but I think is close to what you sent through email.

0 David_Daniels over 2 years ago in reply to Fred Cheng

TI__Mastermind 20135 points

DCAP3 is a version COT. In DCAP3, the on time adjusts in an attempt to maintain a constant switching frequency.

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TPS548A28: Frequency variation of TPS548A28