TPS548A20: Can you please review the schematic?

Hi Kevin

    To help with schematic reviews, we have put together  a schematic/layout checklist and also a reverse calculator to verify your design. Please use them and let us know if you have any specific questions.

Attached here.

Regards,

Gerold

TPS549A20_TPS548A20_Calculator_Checklist.xlsx

Hi Gerold,

Thanks for your prompt feedback.

I will check the schematic with the tool you attached and let you know if I have additional question.

By the way, can you please let me know if you have any advice on adding extra four 560uF capacitors to 3.3V output line?

Regards,

Kevin.

Hi Kevin

Generally speaking large Cout will push double pole to very low frequency. The D-CAP3 device has an internal zero from RAMP circuit. If the double pole frequency is too far away from the zero of RAMP the device has to place Cff (feedforward cap) zero at or around double pole frequency to compensate the phase drop.

So, a place holder to add a feedforward cap would be needed. Also, it would be good to check the design using Pspice simulation to get confidence that you are not running into issues.

Regards,

Gerold

Hi Gerold,

Thanks for your feedback.

But I'm not an expert so I don't know what do you mean exactly.

Could you explain it again more easily?

Regards,

Kevin.

Hi Kevin

     The short answer is when you are using such large capacitance, the device can have stability issues unless compensated properly to address loop stability. 

So, our recommendation is to use a feedforward capacitor of 1nF in parallel with the top resistor (in the feedback divider network).

It is better you take your circuit and run simulations in Pspice to confirm that it works properly before building the board.

You can download Pspice for TI here and the model below that

https://www.ti.com/tool/PSPICE-FOR-TI?keyMatch=PSPICE&tisearch=Search-EN-everything&usecase=GPN

https://www.ti.com/product/TPS548A20?keyMatch=TPS548A20&tisearch=Search-EN-everything&usecase=GPN#design-development##design-tools-simulation

Regards.

Gerold