TPS54620: Connecting two DCDC in series

Izik

Expert 1575 points

Part Number: TPS54620

Hello

I would like to connect two DCDC in series:

12V input -> DCDC1 converts to 5.5V output - >goes to second DCDC input and converts to 3.3V output

Are there any pitfalls or potential problems?

Both work with internal clock

Thanks

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

You can certainly do that. Do you need the 5.5 V rail? If you just need 3.3 it is more efficient to convert directly from 12 V to 3.3 V.

0 Izik over 8 years ago in reply to JohnTucker

Expert 1575 points

Hello John

I do need the 5.5V rail. It goes to a LDO that converts it to 5V
The 3.3V goes to LDO that converts it to 3V

What about noise coming out from DCDC output to input and vice versa? what if they won't work at the same frequency and duty cycle, and each has a different load?

Thanks
Izik

0 JohnTucker over 8 years ago in reply to Izik

TI__Guru**** 191445 points

You can synchronize both to a common clock to have the same frequency exactly. I like to run both converters out of phase with the other to minimize noise. The second converter will definitely put some input ripple back onto the output of the first converter. You can add an additional LC filter after the first converter output LC. Make sure to use some electrolytic capacitance (value not critical) between the second inductor and the input bypass capacitors to the second 3.3 V converter. Lots of users just run the two converters in RT mode and let the frequency artifacts fall where they may if you don't want to generate a sync clock.

0 Izik over 8 years ago in reply to JohnTucker

Expert 1575 points

Thanks!

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TPS54620: Connecting two DCDC in series