LM5117: Compensation filter design for LM5117 in CC/CV

Keshav Raj

Part Number: LM5117
Other Parts Discussed in Thread: LMV431, TLV431, LM76002

Hello,

I am attempting to design a 42V 2A CC/CV buck converter using the LM5117. I am performing CV regulation using an LMV431 and a 20V zener in series to reduce the voltage requirement for the LMV431.

In SNVA829, the example design has a compensation filter with Rcomp of 1k, however it is unknown how this value was calculated. From the related question, the value of Rcomp can be calculated using the top resistor in the divider as Rfb2 which generates the Vref for the TLV431. However the result of this calculation is a very high resistance, much higher than the 1k in the example design.

I am unsure of how Rcomp in this case is calculated for CV/CC and any help is appreciated.

Cheers,

Keshav

over 2 years ago

0 Andy Chen over 2 years ago

TI__Mastermind 27045 points

Hi Keshav,

What's the maximum input in your application? and the switching freq you preferred?

B R

Andy

0 Keshav Raj over 2 years ago in reply to Andy Chen

Prodigy 170 points

Hi Andy,

The input to the converter is a regulated 48V from an external power supply. I have selected a switching frequency of 220KHz.

Cheers,

Keshav

0 Andy Chen over 2 years ago in reply to Keshav Raj

TI__Mastermind 27045 points

Hi Keshav,

as the input is stable 48V and load current is only 2A, I suggest to use converter like LM76002 for this application. you can use CC/CV circuit as introduced on Fig1 on SNVA829.

B R

Andy

0 Keshav Raj over 2 years ago in reply to Andy Chen

Prodigy 170 points

Hi Andy,

I suppose I could use another controller and monitor current myself.

But is developing a compensation filter for the LM5117 in CC/CV prohibitively difficult as I already have several LM5117s lying about and the built in current monitor helps shrink the BOM as I don't need my own current amplifier. It's mostly a matter of convenience.

I could also implement the design and tune the filter manually.

Cheers,

Keshav

0 Andy Chen over 2 years ago in reply to Keshav Raj

TI__Mastermind 27045 points

Hi Keshav,

You can download the Calculator to support the circuit design:

https://www.ti.com/tool/LM5117QUICK-CALC

B R

Andy

+1 Keshav Raj over 2 years ago in reply to Andy Chen

Prodigy 170 points

Hi Andy,

Thanks for the reply, unfortunately the quickstart calculator leads to the same problem once again on the calculation of Rcomp as the feedback mechanism in CC/CV is quite different to the just CV regulator the calculator is designed for.

At this point, I reckon I will start with the values in SNVA829's example design and tune them experimentally.

Cheers,

Keshav

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LM5117: Compensation filter design for LM5117 in CC/CV