PMP8740

anjana salgaonkar

Dear Roberto,

Good Morning, have a great day ahead!

If I selected VADEL=0.2 then, as per your suggestion and calculations given in SLUA560C I got values as RDA1(R5)=8.25K, RDA2(R16)= 348Ohm, And if i want 600nSec delay then RDELAB= 52.5K (so selected 49.9K) is it OK?

Another thing, i used ADELEF resistor network i.e. R6=8.25K and R17=348Ohm and R11=49.9K is OK? or i should change those values too?

Thanks,

Anjana

over 5 years ago

0 anjana salgaonkar over 5 years ago

Expert 1460 points

Dear Roberto,

With R5=8.25K and R16=348Ohm and R9, R10=49.9K i got 600nSec of dead time.

Waveform of OUT-A, Out-B, OUT-c, OUT-D and Gate to Source waveforms of Q8, Q15 and Q9, Q16 are attached

Anjana

0 Roberto S. over 5 years ago

TI__Expert 5225 points

Dear Anjana,
I can say that with these values the delay times are OK. Later you can optimize them.
Also for ADELEF I would keep the values you have: R6=8.25K and R17=348Ohm and R11=49.9K .
Best regards,
Roberto

0 Roberto S. over 5 years ago in reply to anjana salgaonkar

TI__Expert 5225 points

Dear Anjana,
I am happy to see that you measure the delay times that you calculated :-).
Regards,
Roberto

0 anjana salgaonkar over 5 years ago in reply to Roberto S.

Expert 1460 points

Yes...thanks dear.

Today while powering up the dcdc i come to know that zvs diodes D7andD10 are got shorted at the time when CT got damaged...rest Mosfets and gate drives are showing OK on multimeter. What would be the reason for diode damage?

Anjana

0 Roberto S. over 5 years ago in reply to anjana salgaonkar

TI__Expert 5225 points

Hi Anjana,
The ZVS diodes D7 and D10 can get damaged if they recover too much energy from the transformer leakage inductance (and there is not enough cooling provided to them), or the transformer T1 has too high leakage inductance (and the board layout too much parasitic inductance). In this last case, you may see high voltage spikes on Q8 and Q9 drain as well as D7 cathode.
Regards,
Roberto

0 anjana salgaonkar over 5 years ago in reply to Roberto S.

Expert 1460 points

Dear Roberto!

I got the reason why my Diodes get damaged...the diode i received from vendor are of 60V/ 3A rating instead of 600V/3A.

Anjana

0 Roberto S. over 5 years ago in reply to anjana salgaonkar

TI__Expert 5225 points

OK, understood! Thanks for the feedback.
BR, Roberto

0 anjana salgaonkar over 5 years ago in reply to Roberto S.

Expert 1460 points

Dear Roberto,

can you share waveforms of DC-DC board . like drain to source wf of primary switches and synchronous rectifier switches . also transformer primary and secondary waveforms with amplitude.

it will be fine if you draw them and send. please do the needful.

Thanks,

Anjana

0 Roberto S. over 5 years ago in reply to anjana salgaonkar

TI__Expert 5225 points

Dear Anjana,

The plan is to make a more extensive measurements on my prototype by the end of this month, and upload al documents as TI-Design.

I attached the waveformsPMP8740 Rev_B Waveforms.zip I took at the time I developed the power stage. Please let me know if they are OK or you have questions.

Best regards,

Roberto

0 anjana salgaonkar over 5 years ago in reply to Roberto S.

Expert 1460 points

Dear Roberto,

Thanks a lot for waveforms.

Actually i was wondering that transformer primary waveform i got was of amplitude 360Vp-p when input DC voltage was 176VDC.

Thanks,

Anjana

0 Roberto S. over 5 years ago in reply to anjana salgaonkar

TI__Expert 5225 points

Dear Anjana,

A full bridge topology works by applying Vin to the transformer (during the first half cycle) and -Vin during the remaining half cycle. That means you see on the transformer (differential) Vin - (-Vin) = 2Vin; if your Vin is 176V, then you measure 352 V peak-peak.

Best regards,

Roberto

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PMP8740