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RC4580: Inquiry on RC4580IDR under external voltage applied to output pin without supply

Conor
Guru 13415 points

Part Number: RC4580

Hi,

We are using the TI operational amplifier RC4580IDR in our product.

As shown in the attached circuit diagram, there is a situation where the op amp’s supply pins (+V, –V) are left floating (no power applied), while an external measurement instrument (LCR meter: 1 Vrms, 1 kHz) applies voltage to the output pin (OUT).

In this condition, could the RC4580IDR be damaged or degraded due to reverse current flowing into the device through internal protection structures?
Also, should such usage be strictly avoided, and if so, do you have any recommended countermeasures (such as series resistors or external protection diodes) to ensure safe operation?

We would greatly appreciate your guidance.

Best regards,

Conor

  • 0
    TI__Genius 14545 points

    Hi Conor,

    Yes, you are correct; there are diodes to the negative supply and positive supply that you need to be aware of.

    Even if the power supply is "high-z", no power applied, there should still be decoupling capacitors.

    The following app. note has a good description of ESD protection in op amps:

    https://www.ti.com/lit/an/spva018/spva018.pdf

    In general, if you can limit the current back into the device to 10 mA with a resistor on the output, then this should not cause any failures.  But you also need to consider that the supply voltage can be pulled up/down by this reverse conduction.  If the voltage is low, then this probably is not a risk. 

    In higher voltages or power cases where the output can be driven past the supply voltages, we typically recommend the addition of Schottky diodes:

    The Schottky diodes will help clamp the output voltage such that the internal ESD protection is not conducting at a dangerous current. 

    I hope this helps answer the questions here.

    Regards,
    Mike