TPS23750: Rz, Cz selection of Buck Convertor

tateo yamashiro

Guru 10890 points

Part Number: TPS23750
Other Parts Discussed in Thread: TPS54620

Hi,

We got a question from the customer about TPS23750.
Could you help us?

[Question]
They want to make sure how to select Rz and Cz of buck convertor. Is there any equations for this?

Best Regards,
tateo

over 6 years ago

0 Darwin Fernandez over 6 years ago

TI__Mastermind 40530 points

Hi Tateo,

The selection of the compensation network (Type II compensation in this case) should be chosen based on the converter's desired bandwidth of the buck converter.

In general though,

The zero is fz=1/(2xPIxRzxCz)

The pole is fp=1/(2xPIxRzxCparallel); typicall Cparallel is much smaller than Cz

Regards,

Darwin

0 tateo yamashiro over 6 years ago in reply to Darwin Fernandez

Guru 10890 points

Hi, Thank you for your reply. Let me confirm one thing.

How can we determine the Rz? I checked the datasheet of TPS54620 about current mode compensation. So I think it is related to the GM amplifier gain and the power stage gain. Could you provide these values? Or if there is recommended range of Rz, could you provide this?

Best Regards,
tateo

0 Darwin Fernandez over 6 years ago in reply to tateo yamashiro

TI__Mastermind 40530 points

Hi Tateo,

Yes the Rz will affect the crossover. It will also affect the gain. I think the best approach is to design similar to our EVM or TI Designs which use common PoE output voltages and are known working DCDC designs.

EVM can do 5V or 3.3V with BOM change.
www.ti.com/.../tps23750evm-107

While our PMP4679 is designed for 12V.
http://www.ti.com/tool/PMP4679

0 Darwin Fernandez over 6 years ago in reply to Darwin Fernandez

TI__Mastermind 40530 points

Hi Tateo,

Has your question been resolved? If so please click the resolved button to close this thread. Thanks!

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TPS23750: Rz, Cz selection of Buck Convertor