TPS23758EVM-080: DTHR

Hi Zen,

Thanks for reaching out on E2E!

Our Dallas office is closed on Holiday. An expert will get back to you soon!

Thank you,

Kevin

Hi Zen,

Thanks for your patience.

 *Based on

You will have f_m = f_sw / (5000*2.052*C_DTR*1e6), in Hz. f_m is normally 11 kHz for 250-kHz f_sw, so you can choose your C_DTR accordingly.

*f_m needs to be larger than the 9-kHz resolution bandwidth. And f_m normally is not too high to avoid transformer saturation. For the 250-kHz example, 11-kHz f_m offers +- 33-kHz dithering which is normally ok.

Best regards,

Diang

Hi  Diang Xing

  thanks your reply.

  Because the power transformer have high frequency voice, but very very small.

  I try to do some experiments (charge transformer's inductance value and switch frequency..).

  at last, it's the best result (change C_DTR).

  Now, set switch frequency=248KHz, and f_m=20KHz.

  Simultaneously, I did charge load testing (low to high and high  to low) that is OK.

  So, the experiments is ok?  have others suggestion?

thanks

B.R

Zen

Hi Zen,

Thanks for your follow-up.

The frequency dithering is mainly used to reduce EMI to pass the EMC compliance testing.

The hearable voice may be not sufficient enough to say the dithering configuration is ok or not.

Best regards,

Diang

Hi Diang xing
  Thanks for your reply again
   Maybe resonance frequency cause the voice. 
   If the frequency dithering is above 13KHz, the voice will disappear. (that is test result)
   I will test EMI/EMC again.
   

thanks

B.R

Zen

Hi Zen,

Thanks for your reply.

I feel it should be ok to have 13 kHz or higher modulation frequency if:

1. The output voltage regulation is stable enough with dc and transient load (also show enough margins in feedback loop Bode plot).

2. No components are overheated.

3. The board can pass the EMC compliance testing.

Best regards,

Diang

Hi Diang

   How to measure feedback loop Bode plot on TPS23758 (PSR mode)?

   as follows,

    R19//R24--> measure feedback loop Bode?

   If want to adjust phase margin , I can change C28/R22 value. this's right?

thanks

B.R

Zen

Hi Diang

    thanks your information.

B.R

Zen

Hi Zen,

No problem. Good luck for your test! 

I will close this thread for now. If you have further questions, you could open a new thread.

Best regards,

Diang