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INA281: Unpowered

Terho Salmijärvi
Prodigy 10 points

Part Number: INA281

Hello,

We have INA281B3 to measure charging current to a 7 cell battery (VBAT). When battery-operated, the current goes in opposite direction and no need to measure current.

When not charging we want to disable current measurement to save overall power. Therefore we have mosfet's which disconnects INA281 from VBAT.

INA281 is not powered at this time.

(In the schematics we have INA280A3 but we are planning to change it to INA281B3)

If we remove T13 and T14 and have always connection from VBAT to IN- and IN+ AND INA281 is not powered from 3.3V_Vcc, is this ok?

We have tried this and the current in from VBAT to INA281 is very low. Datasheet does not say anything about such scenario.

Now the question:

Is it ok by design of INA281 to do so? 

Best Regards

Terho

  • 0
    TI__Mastermind 33540 points

    Hello Terho,

    This device are allowed to have the Input voltage above the supply voltage so you will not have issues damaging the device.  The input bias current will change as Vsense (VDifference at input).  Both these plots are seen in the datasheet on IB vs VCM and IB vs Vsense with Vs = 0V.  This is ok to do. 

    BTW.  You will add error by placing the 100Ω (R83 and R84) if you can lower it you will increase your accuracy.  Also what is the purpose of R80?  I do not think you need that resistor.

  • 0 in reply to Javier Contreras4
    Prodigy 10 points

    Hello Javier,

    I see it now. IB and VCM is specified when Vs=0V. I missed this when reading datasheet.

    We will decrease R83 and R84. We missed this also when reading datasheet. Max 10R.

    You are right about R80. It is in parallel with the shunt and has no meaning.

    Thank you very much. I really appreciated your help.  

    Best Regards

    Terho