ADG824 / ADG884 switch impedances with Vdd=0

Hi,

We are considering using either the ADG824 or the ADG884 dual SPDT analog switches, however our application requires the switch analog terminals to be in a high-Z state with the device Vdd=0 V as audio signals are still likely to be present even with Vdd=0.

I cannot find this information in the datasheet, so I would like to know if this is the case or not ? Are the switches in High-Z states when no power is applied to the device Vdd ?

Looking forward to your reply.

Regards, Mike

  • 0
    •  Analog Employees 
    on Nov 9, 2017 6:42 PM

    Hi Mike,

    Yes, you are correct. When Vdd=0V the switches are turned off of in high impedance. However, when an audio signals are present and Vdd = 0V, you are risking the overvoltage event.

    Let me explain it this way, the source and drain terminals have clamping diodes to the supplies to provide ESD protection, as illustrated in the figure below. In normal operation (Vdd is present) these ESD diodes are in reverse-biased and will not pass current. But when the analog inputs exceed the supplies, in your case audio signals are present while Vdd=0V, the input signals can forward-bias the ESD diodes and begin to conduct.

    For your application, when audio signals are still likely to be present even with Vdd=0, I would recommend to use the ADG4612 which is a Quad SPST switch with Power-Off protection and low on resitance of 5ohms. The SPST switches can be configured to a dual SPDT switch. When no power supplies are present, the switch remains in the off condition. The switch inputs present a high impedance, limiting current flow that could damage the switch or downstream circuitry. 

    Let me know if this helps.

    Best Regards,

    May