ADA4610-1 huge supply current

Hi Everyone,

I am using an ADA4610-1 opamp in an active loop filter for a PLL. However, after soldering it on my PCB, with the PLL turned off (no supply voltage, so no current on the charge pump output either) and giving 25V single supply voltage to the opamp, the input current is not a few mA as in the datasheet but 70mA (!!!). It increases with increasing supply voltage. What could cause this? Similar problems arised using another amplifier on another PCB. That time the opamp got really hot, now I disconnected the voltage immediately as soon as I saw the current measurement on the supply, because I wouldn't like to blow it up.

I have triple-checked my board and the soldering of the pins, there are no shorts.

I enclosed the relevant part of my schematic.

  • Hi cseppento, 

    Can you confirm to what voltage level the inverting input is biased to when the supply current increases? It must be ensured that the voltage is within the input voltage range (2.5 to 22.5V for your case) of the device. Without the connections of the previous stage at CPout, it seems like the inputs are floating.

    If this is the case, or if the inputs are set to anywhere outside the input voltage range, I suspect the outputs may be railing. 

    Also, a question regarding your circuit in general. I notice you have a single supply of 25V. What input levels are you expecting from the charge pump? Take note that you would have a gain of about -5 in your configuration. If these inputs are positive, you will either need a negative supply or some bias voltage at the non-inverting input. Otherwise, you would likely always be railing to ground.

    Thanks, 

    Kris