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VCA810 Can the Control Voltage damage chip

dan kantorski
Intellectual 910 points
Other Parts Discussed in Thread: VCA810, DAC8532

Hello:

I am working with the VCA810 and have subjected it to a -2.9V control voltage, I have read in the application notes that voltages below -2.5V should be avoided to prevent saturation.  Is it possible that subjecting the below that threshold will damage the IC.  I had baised a DAC in the system to operated between 0-1.9V to get a maximum amplification of a power amp.  Using an analog switch, the circuit is flexible to allow an AGC to drive the VCA810.  I had installed a 2.2V zener on the output of the AGC to protect against a voltage under -2.2; however, this circuit did not do what I had intended and have put -2.9 into the VCA. 

I have went back to driving the VCA with the DAC circuit and find that the max value on the amp has changed to something much lower.

Could the VCA810 now be damaged?

  • 0
    TI__Genius 17905 points

    Dan,

    The VCA810 may have been damaged as the datasheet warns against saturation and latching with applied Vc voltages lower than -2.5V. Would it be possible to replace the VCA810 IC on your board with a new one? That would be a straightforward way to test if the part was damaged or if there is an issue elsewhere.

    When your system powers up, is there a possibility that the voltage at Vc still goes below -2.5V even after reverting to your original circuit?

  • 0 in reply to Kris F
    Intellectual 910 points

    In the normal system on state the switches are set to allow the DAC8532 to operate the VCA.  I have an opamp circuit to invert and attenuate the DAC voltage.  The DAC is set to active but should be set to 0V level up at system start so I would say no.  The issue is I have a 2.2V zener operating in negative mode with a 1k series resistor and the thing decides to regulate at -2.9V????  So, the saturation of the VCA might have damaged itself yielding less maximum output?  I need to figure out what to do for protection before I insert a new part.  The VCA still works, maybe just not to its full potential, I think.

    Thank you for your response.

  • 0 in reply to dan kantorski
    TI__Genius 17905 points

    Dan,

    I briefly spoke with the designer who said that he would expect potential damage if the voltage at Vc went as low as -4 or -5V. That being said, perhaps the device is not damaged but the circuit needs to be modified.

    Can you please share a schematic drawing including the DAC, inverting op amp, Zener (with part number), and VCA810? I want to understand your configuration better.

    What is the measured voltage at the Vc pin when you measure the VCA810 output? What is the VCA810 output when you remove the Zener circuit completely? Try replacing the Zener and series resistor with just a resistor to ground.

  • 0 in reply to Kris F
    Intellectual 910 points

    I have talked to the diode manufacturer and he stated the zener voltage was based at a certain current level.  This was my mistake.  I have increased the resistance to the specification for the zener and have it regulating properly now.  I have not yet replaced the VCA part yet but I will.  When I was directly controlling the VCA with the DAC, I had a bias point of Vc=1.85V to achieve maximum output and this has changed, Now Vc=1.9V will not yield maximum output. so I am quite certain I may have damaged something in this process.

    Thank you for your assistance, and will post again or contact you directly if I need additional help.