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OPA340, OPA347 unpowered input to output leakage

Sean Byrne
Prodigy 80 points
Other Parts Discussed in Thread: OPA340, OPA347

I'm looking to use an OPA340 or OPA347 as a simple comparator to monitor the voltage of the BR2032 battery.  When the opamp is unpowered, if there any possibility of significant (nA) leakage from IN+ to OUT?  The battery powers an RTC in the absence of main power and I don't want any additional draws on the battery other than the RTC.  Both devices list a 10Tohm input impedance - is this also the case when the device is unpowered?

  • 0
    TI__Guru 62700 points

    Sean,

    If the OPA340 or OPA347 have both power supplies and IN+ floating, there is no possibility of significant current leakage from IN+ to OUT. 

    However, if unpowered op amp means supplies are grounded (0V), the current leakage will depend on the input voltage applied to IN+:

    1. if IN+ is left floating, no significant leakage will occur

    2. if IN+ is driven above or below ground, one of the ESD protection diodes between IN+ and each of the rails will turn-on and the leakage will depend on the actual input voltage at IN+ (forward bias of ESD protection diode).

  • 0 in reply to Marek Lis
    TI__Expert 6275 points

    You will be interested in this blog post below:

    http://e2e.ti.com/blogs_/b/precisionhub/archive/2014/02/11/the-mystery-of-the-depleted-coin-cell.aspx

  • 0 in reply to Tim Green1
    Prodigy 80 points

    Tim, Marek - thanks for your help.  The blog post lists TLV245x as a part with an ESD protection scheme that will not result in unpowered leakage.  I'm wondering is there is a less expensive part (more in the $0.15 to $0.25 price range @1k qty) that also has a suitable ESD protection scheme.