INA181: Design recomendation

max r

Part Number: INA181
Other Parts Discussed in Thread: LM393LV

Tool/software:

Hello,

I am wondering if the INA181 is the right part for my design. I am trying to create a board which can sense current => 5mA and toggle an optocoupler. The rails powering the load switch frequently between 0-19V (one moment one rail will be 19v and one rail will be 0V, the next moment they will switch i.e. Vpp ~38V).

Best,

2 months ago

0 max r 2 months ago

Prodigy 10 points

Hi,

I should clarify the bus voltage is never Vpp = 38V at a single time. Rather the 19V switches polarity.

Best,

0 Clemens Ladisch 2 months ago

Guru 276380 points

Please show a schematic. (What is important is the voltage relative to the INA181's GND.)

0 max r 2 months ago in reply to Clemens Ladisch

Prodigy 10 points

Hi Clemens,

Thanks for the reply. I have not done a whole schematic yet as I am trying to evaluate if this fits my application so please excuse my poor drawings of my current proposal. In this case the goal is to toggle the optocoupler whenever current draw from the load exceeds roughly 5mA (regardless of polarity of Vbus).

best,

0 Clemens Ladisch 2 months ago in reply to max r

Guru 276380 points

I assume Vbus/Rsense is connected to GND somewhere?

The INA181 supports negative inputs down to −0.2 V. In this application, it never sees the full bus voltage.

The INA181 outputs an analog signal near 2.5 V. To enable the optocoupler when the current is above 5 mV or below −0.5 mV, you would need two comparators, e.g., LM393LV.

0 Mallika Senthil 2 months ago in reply to max r

TI__Intellectual 2000 points

Hi Max,

The INA181 could work for you application, but as Clemens said, you'd probably need two comparators to turn on and off your optocoupler at one specific desired current (5mA) since optocouplers have a current range within which they get toggled on or off. Another option would be to pick one of our current sense amplifiers that have a window comparator built in, like the INA310.
Here's a link to more similar devices.
https://www.ti.com/amplifier-circuit/current-sense/analog-output/products.html#3278=Analog%20output%20with%20integrated%20comparator&726max=40%3B120&

Best,
Mallika Senthil

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INA181: Design recomendation