# HMC980LP4E Vgate, Vneg, Idrain question

Question asked by Eunki on Apr 27, 2016
Latest reply on May 11, 2016 by kkaya

HI.

I'am using HMC980LP4E RF amp bias controller.

If desired Vneg
< -2.46 V,

• R5(kOhm)  = Open
• R6(kOhm) = E1 / [
E1*(desiredVneg-E5) / (E2*(E5-E3)) -1 ]

If desired Vneg
> -2.46 V,

• R5(kOhm) = E2 / [
E2*(E3-E5) / (E1*(E5-desiredVneg)) -1 ]
• R6(kOhm) = Open

If desired Vgate
< -2.46 V,

• R7(kOhm)  = Open
• R8(kOhm) = E1 / [ E1*(desiredVgate-E5) / (E2*(E5-E3)) -1 ]

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• R8(kOhm) = Open

Where, E1=50, E2=262, E3=1.44 and E5=0.815.

I wanted each output to be, Vneg : -1.8V And Vgate : -1.5V, so by formula Vneg feedback resistor(1M), Vgate feedback resistor(634k) are set as 1MOhm and 637kOhm respectively.

Vneg showed -1.8V as I want however, Vgate was -0.5V which is much smaller than as intended (-1.5V).

Also, Even though the set value to 137 ohms Rsense, Idrain output is approximately 0.6A.

Picture below is the circuit configuration.

Also I have tried changing the Vgate feedback resistor to different value (470k), however, Vgate didn’t change.

First, by considering the picture above, can you find a problem to the circuit?

If there is none, can you suggest a way the fit the Vgate as I want it to be?

Thank you.

Best regards.