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INA168/138 input current

Hi,

I'm planning to use the TI INA138 current-chunt monitor to measure the load current out of a 6-cell NiMh pack. The INA138 will be permanently connected.

I'm keen to keep the standby current from the battery to a minimum when the product is powered off; the datasheet says the worst-case current into either of the sense pins is 10uA (which is fine). What it doesn't say is whether this still holds with the Vcc pin tied to GND - the 5V rail powering this pin also powers a bunch of other stuff, which will have a fairly-low resistance path to GND when it's off.

I've been bitten like this before with protection diodes etc which aren't shown on the equivalent circuit, anybody have any experience with this part? The fall-back plan is to isolate the 138 inputs with a pair of PMOS's, but it'd be a lot neater if this wasn't necessary.

TIA

R.

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It's pretty clear that there are no protection diodes...

"INDEPENDENT SUPPLY AND INPUT COMMONMODE VOLTAGES"

About the only way you're going to know is to try it. I would hazard a guess that the only sneak-path might be the output (when VDD is removed)... put an analog switch in series with the emitter (output).

...Jim Thompson

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| James E.Thompson, P.E.                           |    mens     |
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Jim Thompson

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