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VCA810: DC input

K.Hamamoto
Guru 12155 points
Part Number: VCA810

Hi

There is the characteristics graph of frequency and gain on the datasheet. 

What does this graph mean? Is DC(=low frequency) input acceptable?

Our customer measured the output voltage with DC input (+IN=-0.5V and -IN=GND). However it was not change by any VC voltage.

I would like to know what the above graph mean.

Regards,

Koji Hamamoto

  • 0
    TI__Genius 15975 points

    Hi Koji-san,

    Sorry for the delay in response.

    For the VCA810, DC input is acceptable. The graph shown above gives the power supply rejection ratio on the positive supply (PSRR+) for gain control at Max Gain. This graph is not related to the gain achieved for different gain control voltage setting, which is instead shown on Figure 6 of the datasheet.

    If I look at the customer schematic, it seems the polarity on the electrolytic cap is reversed on the -5V supply. Could this be the reason for no measured output voltage with +IN = -0.5V and -IN = GND? The correct polarity should be as shown below.

    Best Regards,

    Rohit

  • 0 in reply to Rohit Bhat
    Guru 12155 points
    Hi

    I am sorry for the delay in my reply.

    It was my mistakes. On their board, it is correct connection as you pointed.

    The our problem is that the output is -0.9V when +IN = -0.5V(DC input) and VC=-1V(0dB) at the above circuit.
    -0.9V is correct? I thought it will be -0.5V because the gain is 0dB.

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Genius 15975 points
    Hi Koji-san,

    I believe the understanding is correct that with +IN = -0.5V and VC = -1V (0dB gain), you should measure -0.5V at the output.
    Let me ask you as to what node in the above schematic the -0.9V is being measured? Is it before the 100k resistor directly at the VCA810 output or is it after the 100k resistor? Also, could you try to apply +IN = +0.5V keeping VC = -1V (0dB gain) and make sure the VCA810 output is at +0.5V?

    Best Regards,
    Rohit