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TPS53511 output voltage setting over 2.5V equation

Dear folks,

I faced to the problem that how to compute R value for setting output Voltage as 5.5V expected.

datasheet equation (8) is funny like below...

'Vout' appears Left and Right in equation.

Why datasheet presents such a funny description ?

(5.5V output expected)

Thanks for help,

  • That is an old equation used to fine tune the output for higher voltages. The difference is less than the amount of variation for standard E96 resistor values. Take the 5 V case. If you assume R2 = 10.0 k, then using the first simple equation gives R1 = 55.359 k. Closest standard value is 54.9 k. the calculated Vout using those resistors in the top equation is 4.965 V. Using the bottom equation you get 5.020 V, a 55 mV difference. Changing to the next closest standard value of 56.2 k, gives 5.064 V using the top and 5.112 V using the bottom equation. So if you are going to use multiple resistors in series to get precisely set your output, you can use the bottom equation. If you are going to use single standard value E96 resistors for R1 and R2, you can just use the top equation. It will give you the same standard value. We have deleted that second equation from some of our more recent product datasheets.