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ADA4932 /PD pin

Update to a problem I found with an ADA4932-1 concerning the PD pin.

I have two circuits using this device, one is a balanced MFB active filter, the other a 2X analog line driver.

The MFB active filter uses a single 5V supply, the bus driver uses a symmetrical +-4.25V supply.

Both circuits use the /PD pins to conserve power.

The problem I see is that enabling the active filter at low temperatures, causes BOTH +ve and -ve outputs of the device to go to the positive rail (or at least within 1.2V of the rail). This condition can last 100s of milliseconds, depending on the temperature, so it seems like a leakage current issue combined with some capacitive charging/discharging.

The analog line driver does not suffer from this problem, either because the /PD function works as expected with the dual supply, or because there are no (large-ish) capacitors in the feedback network (as is the case for the active filter).

My question is, does the /PD function work properly with a single supply ?

  • Hi RFRM-

    I noticed that you created a separate group for this question.  Since groups you create like this aren't actively monitored, I've moved this question to the Differential Amplifiers Community where you should be able to receive an answer.  I would suggest posting your questions related to this part here.



    EngineerZone Community Manager

  • Hi RFRM,

    I apologies for the delayed response,

    I wanted to make sure I was able to go into the lab to repeat your test and see if I get the same results.

    Since this question will require some testing in the lab we will work with you off-line and post the result to this thread later on.

    I’ll contact you via private message with more information.I will keep you updated for further investigations.


    Charly El-khoury

    Added note about contacting customer directly.

  • Hi Charly,

    I appreciate your response.

    We are using the devices with a single supply at +5V, maybe this affects

    the performance adversely ? VCMO is set at 2.5V by an external buffer.

    We begin to see issues at about 5C, and the time taken to begin

    operating correctly increases rapidly as the temperature is lowered

    further. At -15 we were seeing a 'recovery' time of the order of 30s or


    We have disabled the function in our system, we'll have to accept the

    increased power consumption.

    Perhaps you could answer another question for me, is this the lowest

    noise part in the AD range at this performance ?

    Thanks and regards


  • Hi Roger,

    Depending on the duty cycle of part "ON" vs "OFF", maybe you can try the ADA4927 instead of the ADA4932.

    It's double the power (20mA instead of 9.6ma) and 1/2.5 the noise (1.4nV/rtHz instead of the 3.6nV/rtHz)

    It's in the same package as the ADA4932. the only disadvantage is the Feedback resistor has to be whatever

    is recommended by the datasheet and the differential output swing might be about 400mV less with the ADA4927. 

    Would this help your current product you think?

    I'm happy to work with you to get your system working and getting the best performance possible.


    Charly El-Khoury

  • Hi Charly, thanks for that, I've studied the ADA4927 data sheet, I think

    the low input impedance may be a problem, I will investigate further.

    I did notice that there is a paragraph is the data sheet for the ADA4927

    warning about not using power down feature at low temperatures, shame

    this warning does not appear in the ADA4932 data sheet also !

    Thanks you for your help.


  • This question has been assumed as answered either offline via email or with a multi-part answer. This question has now been closed out. If you have an inquiry related to this topic please post a new question in the applicable product forum.

    Thank you,
    EZ Admin