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INA169: Bidirectional Current Sense INA169/7 vs LMP8480/1

AJ
Intellectual 570 points
Part Number: INA169
Other Parts Discussed in Thread: LMP8480, , INA170, LMP8481, LMP8640HV, INA240

Hello Support,

I am investigating possible current sense solutions in our application.

The input voltage is battery powered Vin: 10V ~ 40V and the continuous load current rating is 25A with spikes up to 50A.
Additionally, since it's battery powered, there is a charge current path and the max current is 2.5A. 

I am considering bi-directional current sense, however because Rsense/GAIN are fixed the concern is accuracy for low currents when charging, i.e. < 100mA

1) For Uni-directional: what would you recommend INA169 or LMP8480, 

2) For Bi-directional:  what would you recommend INA170 or LMP8481

In terms of accuracy, the LMP848x seems a better option with max Offset/Error 265μV/0.8% vs 1000μV/2.0% for the INA169/170. The limitation is with fixed GAIN of 20, 60 and 100 (I looked and the LMP8640HV does offer adjustable gain but for similar offset to the INA170)

3) general question, What is the pros/cons of current out vs voltage out?

Current output can not be used directly and has to be converted to a voltage by use of external RLoad before it's sampled by the ADC

Cheers,
Alex

  • 0
    TI__Mastermind 26475 points

    Hello Alex,

    Thank you for using the forum.  There are many trade-offs and you may need to focus on the most important.  For example if your highest priority is Offset/Gain error then you cold look at the INA240 although it does have a larger Input bias current.  The INA169 output current makes the change or gain easier with a change of a resistor and the bandwidth is higher.

    The INA240 is limited to 5.5V supply and so would the output.  That is not the case of the INA169, INA170, LMP8480 or the LMP8481 as the supply and output voltages can be much higher if desired.  Keep in mind the offset and IB for your low current measurements as this will be you biggest contributor of error.

    With regards to the current output vs voltage output you can see the INA169 has higher bandwidth and with current output you could do some designs that would be better suited with currents such as voltage shifting (see this circuit) or changing the gain by simply changing the output resistor.