Hi,

Any recommendations about selecting the bottom feedback resistor?

In the datasheet a use case of 115K ohm is shown, but it fits for 3.3V.

I need to produce output voltages of 12V up to 33V.

Thanks,

Kobi

Hi,

Any recommendations about selecting the bottom feedback resistor?

In the datasheet a use case of 115K ohm is shown, but it fits for 3.3V.

I need to produce output voltages of 12V up to 33V.

Thanks,

Kobi

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Hi Kobi,

The 115K ohm for bottom resistor is still fits for the 12V and 33V VOUT.

It has a good balance in terms of power dissipation (VOUT^2/Rfb_total) and error (cause by Ifb * Rtop).

Example:

For 33V use case,

Rbottom = 115 K ohm (std value)

Rtop = 4.64M ohm (std value)

VOUT = 33.078V

Power dissipation across FB resistors = 230uW

Error (Ifb * Rtop) = 0.1uA * 4.64M ohm = +464mV (max)

% Error_total_max = {[(33.078V + 0.464V) - 33V]/33}*100% = 1.64% (max)

Thus, for 12V up to 33V operation (I assume you'll be using adjustable resistor for Rtop - can you confirm? or perhaps give us some insight in your application), Rtop range = 1.61 M ohm to 4.64 M ohm.

Thanks and regards,

Jefferson

Hi Kobi,

The 115K ohm for bottom resistor is still fits for the 12V and 33V VOUT.

It has a good balance in terms of power dissipation (VOUT^2/Rfb_total) and error (cause by Ifb * Rtop).

Example:

For 33V use case,

Rbottom = 115 K ohm (std value)

Rtop = 4.64M ohm (std value)

VOUT = 33.078V

Power dissipation across FB resistors = 230uW

Error (Ifb * Rtop) = 0.1uA * 4.64M ohm = +464mV (max)

% Error_total_max = {[(33.078V + 0.464V) - 33V]/33}*100% = 1.64% (max)

Thus, for 12V up to 33V operation (I assume you'll be using adjustable resistor for Rtop - can you confirm? or perhaps give us some insight in your application), Rtop range = 1.61 M ohm to 4.64 M ohm.

Thanks and regards,

Jefferson