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vca821 Vout(pp) vs max gain adj range

On its datasheet page 9, figure 3,  I wonder how I could get the value of 20dB from Vpp = 1V on the curve Rf=1kohm ?   ( basically,  how could I use the equation there to get the plot ? )   I tried myself with all equations in the datasheet but still could not reach the algorithm behind this plot. 


  • Hi Duuk,

    I will need some time to look into this.  There is a limit of 2.6mA in the gain set resistor (Rg).  This graph helps to show what size Rf you need based on the output voltage of your signal and the maximum gain you require. 

    Can you give me some details on your desired circuit? What is your desired maximum gain?  What is your desired output voltage?   What range of input / output voltages do you need?

    I will see if I can confirm that the equation in Figure 3 is correct. 



  • Thanks Loren,

    Here is the information -

    Output Vpp = 1V, and max gain is 20dB. (So likely Rf should be 1Kohm, according to fig.3 ). The rest will follow equations in the datasheet. Wonder if that will work ?

  • Hello Duuk,

    I have looked the datasheet figures you referenced and I think they do not apply the way you think they do.  

    If you look at page 15 of the datasheet Figures 32 and 33 show the amplifier with 20dB of maximum gain and various output voltages up to 5Vpp with an Rf of 402 Ohms. 

    For your application maybe you want to increase Rf to 500 Ohms for some margin, but it does not seem to be necessary.