LM27762: LM27762 output voltage formula

Alexander Kaliadin

Prodigy 130 points

Part Number: LM27762

hi,

LM27762 formula for output voltage VOUT =1.2V×(R1 +R2)/R2 got me confused.

With 5V input and R1=R2, formula=5 x 1.2 x 2 = 12V ?

With R1 >> R2 it gets even worse... Am I missing something here?

I need +/-5V (approx) out of +5V input -can somebody help?

Cheers,

Alex

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

That equation is correct. For the positive output the reference is 1.2 V. It forms R1 and R2 form a simple divider so Vref = Vout * R2 / (R1 + R2). rearranging terms gives Vout = Vref * (R1 + R2) / R2. So for R1 = R2 = R, Vout = 1.2 * (R + R) / R = 1.2 * 2 = 2.4 V. The input voltage does not factor into it.

0 Alexander Kaliadin over 8 years ago in reply to JohnTucker

Prodigy 130 points

Ah, got it. I have mistaken V in formula for Vin. Now it makes sense - thanks John.

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LM27762: LM27762 output voltage formula