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I have the following circuit for the LT3463A regulator: https://www.analog.com/media/en/technical-documentation/data-sheets/3463f.pdf

I started testing the board, for the negative voltage I was getting -2.49 which is fine and for the positive voltage I was getting 1.6V which was weird because I chose the resistors based on the datasheet. I measured the FB1 voltage which should have been 1.25V and read 0.6V. I checked the schematic and it was matching to the datasheet.

I did some simulation in LTspice and got similar answers to what I am seeing in my circuit. I am still not sure what I have done in wrong in my schematic and wonder if LT3463A works for lower input voltages like 2V. enter image description here The output seems to be always Vin-400mV regardless, I even pulled SHDN1 to ground and the output does not shutdown. Did I do anything wrong? What do I have to change in order to get +/-2.5V?

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  • \$\begingroup\$ Show your layout. \$\endgroup\$
    – winny
    Jun 23, 2022 at 8:35

2 Answers 2

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Simple enough, the positive regulator is a boost converter and output cannot ever be below input voltage -once granted voltage drop on D1-

enter image description here

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  • \$\begingroup\$ I thought about that too, so I changed my input to 2V which is the minimum input and the output voltage was 1.6V and Vfb voltage was 800mV. From the datasheet, it seems that Vfb have to be a constant 1.25V but that is not what I am seeing \$\endgroup\$
    – Shannon
    Jun 23, 2022 at 8:38
  • \$\begingroup\$ That is with the same equal resistors at the output to give me 2*1.25V \$\endgroup\$
    – Shannon
    Jun 23, 2022 at 8:38
  • \$\begingroup\$ Got it, I changed the input to 2.1V and you're correct \$\endgroup\$
    – Shannon
    Jun 23, 2022 at 8:41
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It's simply the wrong part… the LT3463A is a boost converter so if you feed it 3.5V you can't get a regulated lower voltage on the output.

The topology is easily recognizable since the inductor is on the input and the (internal) switch is toward ground (figure on page 4 of the datasheet shows the internal blocks).

If you try to use it as a step down it will run at a somewhat 0% duty cycle and the drop you see is the internal schottky diode loss (400mV is typical)

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