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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 ?

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  • 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.

    Regards,

    Charly El-Khoury

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  • 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.

    Regards,

    Charly El-Khoury

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