LM25143: DC-DC Converter Design

Abhishek Kumar

Part Number: LM25143
Other Parts Discussed in Thread: TIDA-050014

Tool/software:

Hii,

We want to design a DC-DC converter with an input voltage of 12-24 V and a variable output voltage of 12-20 V, how can we do it with LM25143?

6 months ago

0 Andrew Kutzler 6 months ago

TI__Genius 15780 points

Hi Abishek,

Variable output how? As in if VIN = VOUT when VIN<20V, and then VOUT = 20V when VIN >= 20.

Or do you want to be able to change it on the fly?

Thanks,

Andrew

0 Timothy Hegarty 6 months ago

TI__Guru 63507 points

Hi Abhishek,

I recommend using the LM25143 quickstart calculator: https://www.ti.com/tool/LM5143DESIGN-CALC

Set Vout = 20V first and derate the ceramic output capacitance accordingly. Then fix the compensation values and check the loop with Vout = 12V and the higher Cout value for 12VDC. The crossover frequency should not exceed ~12% of Fsw or 100kHz, whichever is lower.

Regards,

Tim

0 Abhishek Kumar 6 months ago in reply to Andrew Kutzler

Prodigy 40 points

No, the input supply voltage will be 24 V from the battery, and we need a variable output voltage between 12-20 V by controlling its duty ratio.

0 Andrew Kutzler 6 months ago in reply to Abhishek Kumar

TI__Genius 15780 points

Hi Abhishek,

It's technically possible, but this will increase circuit complexity as control signals and MOSFETS are required in order to enable/disable the resistor feedback network to achieve variable VOUT.

TIDA-050014 does this by having a control signal turn on/off various mosfets in the resistor feedback network.

https://www.ti.com/tool/TIDA-050014

Thanks,

Andrew

0 Timothy Hegarty 6 months ago in reply to Andrew Kutzler

TI__Guru 63507 points

In addition to what Andrew mentioned, you can also use a PWM signal from an MCU that is averaged by a couple of RC filter stages and then resistively coupled into the FB node to continuously adjust Vout over the required range.

See Fig. 10 here: https://www.ti.com/lit/an/slyt777/slyt777.pdf

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LM25143: DC-DC Converter Design