LM25116: External feedback voltage

Hello

You can use a DAC to control the output voltage.

Please see the attached for more information.

We will be happy to review your final design when you are ready.

Thanks

0247.DAC_calc5.xlsx

Hi Daniel,

It's better to keep the FB divider intact and resistively couple a current into the FB node to adjust VOUT.

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

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Tim

Thank you

The device has these parameters:

V_R = GND

V_FB = 1.25V

R1 = RFB1 = 3.9kOhm

The DAC can generate voltages between 0 and 10V

We require that this can adjust the output voltage between 0 to 24V

I used your spreadsheet to calculate that the RFB2 (R3) should be 62kOhm and R1 should be 25.8kOhm.

I see that your spreadsheet warns that frequency compensation will probably be necessary. Can you suggest a simple circuit to accomplish this?

Best Regards

Daniel

Hello

Your document indicate that the DAC output must of relatively low impedance.

We have this device that has analog outputs: 

https://www.ni.com/en-za/shop/model/usb-6001.html

Could you advise on whether its output impedance is low enough?

Best Regards

Daniel

Hello

The output impedance should be much less than the resistor values in the divider.

Keep in mind that you will not be able to bring the output all the way down to 0V.

You may need to empirically adjust the compensation for best response.

Thanks