DC-DC converter stability

Vladimir Laukh

Other Parts Discussed in Thread: LMR36006, LMR14006, LM2596

Hey!

I'm implemeting design mentioned in the article https://www.ti.com/lit/an/slyt777/slyt777.pdf?ts=1597909097823 (Fig.10).

I got a problem with stability over desired range of voltages and currents. I tried that design with LMR14006Y part, with no luck - at some output values design unstable.

My goal is to implement buck converter with programmable 3-20 V output, currents are 50 - 300 mA roughly. I'm not sure how to calculate or measure stability with the whole range of loads and voltages. If there is out-of-the-box design it would be great. Ripples at the output doesn't matter at this point because I can filter them afterwards (I think).

Sorry for repost, I'm not sure how to continue old thread.

Thanks!

over 3 years ago

0 Gerold Dhanabalan - Online Design Tools over 3 years ago

TI__Genius 14455 points

What is the input voltage range of the device? Are you trying this on the EVM of LMR14006Y or using simulations?

regards,

Gerold

0 Vladimir Laukh over 3 years ago in reply to Gerold Dhanabalan - Online Design Tools

Prodigy 120 points

Hey Gerold!

Input is 24V, I'm trying this on custom board.

If it's impossible on this part let me know. I'm free to choose another converter. Even with low frequency switching.

0 Gerold Dhanabalan - Online Design Tools over 3 years ago in reply to Vladimir Laukh

TI__Genius 14455 points

It is quite challenging to get a converter work across the wide range of Vout. Using the WEBENCH tool, I was able to pick the LMR36006 - but the design needed a Cff (feedforward capacitor) for low Vouts. What is your application that needs this requirement? In normal applications, typically Vout adjustment is done by a few hundred millivolts to scale up or down depending on processor requirements.

Regards,

gerold

0 Vladimir Laukh over 3 years ago in reply to Gerold Dhanabalan - Online Design Tools

Prodigy 120 points

Yup, I already realized that it's challenging :(

Feedforward capacitor - doesn't mentioned in LMR14006 datasheet, would it help?

My application is the stable current source with fixed output value (up tp 0.3A) for various loads. I use programmable DC voltage for reducing power dissipated on the board, depending on the load.

Also I tried same approach with simple module based on LM2596 - got large ripples ( up to 100 mV), but converter seemed to be stable over 4-20 V / 0.3 A output.

Maybe I should try enormous values on inductor and capacitor? Any other suggestions? Again, I'm not stick to LMR14006, but want to use similar converter (0.6 - 1A maximim) since I don't need large currents and want to use high frequency switching.

0 David Baba over 3 years ago in reply to Vladimir Laukh

TI__Mastermind 29990 points

Hello Vladimir,

Please compete a WEBENCH design for your VOUT Max at for max output power, with Min VIN requirement, and the other output voltages should be stable. Hope this helps?

David.

0 Vladimir Laukh over 3 years ago in reply to David Baba

Prodigy 120 points

Thanks for help!

Power management

Power management forum

DC-DC converter stability