INA180: Using for bidirectional current sensing

Kaushalya Satharasinghe

Part Number: INA180
Other Parts Discussed in Thread: INA181,

Tool/software:

Hi,

I know INA180 is for unidirectional current sensing. But this is cheaper than INA181. What are the consequences of using INA180 for bidirectional current sensing? I think the output is only activated for positive half cycle. As long as common mode is not violated, is it ok to use in bidirectional current sensing?

Cheers,

Kaushalya

9 months ago

0 Mallika Senthil 9 months ago

TI__Expert 7880 points

Hi Kaushalya,

We don't recommend using the INA180 as a bidirectional device because it doesn't have a REF pin for you to bias up the signal, ensuring that the output doesn't go below (GND-0.3V) or (Vs+0.3V).

However, if you do decide to use the INA180, you must ensure that common mode and abs max ratings is not violated, so as to not damage the device.

Best,
Mallika Senthil

0 Kaushalya Satharasinghe 9 months ago in reply to Mallika Senthil

Prodigy 240 points

Hi Mallika,

Many thanks for your reply. I am not interested in a ratiomatric measurement, just detection of current above a certain level. So I dont need to add a ref. I feed the output of the INA180 to a retriggarable monostable to get a clean pulse.

The way I have used INA180 is as follows.

The Vcm requirement is satisfied by having a floating GND. I have prototyped the design and seems all good. Do you see any caveats in this design?

Cheers,

Kaushalya

0 Mallika Senthil 9 months ago in reply to Kaushalya Satharasinghe

TI__Expert 7880 points

Hi Kaushalya,

I'm looking into this, I'll get back to you.

Best,
Mallika Senthil

0 Mallika Senthil 9 months ago in reply to Kaushalya Satharasinghe

TI__Expert 7880 points

Hi Kaushalya,

I'm not sure why the regulated 3.3V would need to be tied to the 24V AC on the secondary, could you please explain why?
Also, I'm a little concerned about the -24Vac connected to the load, this may lead to Vcm violation.
Please see the following app note for reference, they use the INA180 in a bidirectional application.

https://www.ti.com/lit/an/sboa529/sboa529.pdf

Best,
Mallika Senthil

0 Kaushalya Satharasinghe 9 months ago in reply to Mallika Senthil

Prodigy 240 points

Hi Mallika,

The 3V3 is tied to 24V to get the GND floating below 3V3 from 24V. As you can see from the image, the GND is floating in this design. This way we can get the Vm requirements satisfied. Also I use the 3V3 to power the MCU which direct drive the TRIACs. By tying 3V3 rail to 24V rail, I can operate the TRIACs gate drive in most efficient quadrants.

Cheers,

Kaushalya

0 Mallika Senthil 9 months ago in reply to Kaushalya Satharasinghe

TI__Expert 7880 points

Hi Kaushalya,

What is the voltage at the following nodes highlighted in the imager below and how do you ensure the voltage to INA180 (-) sense line doesn't go below GND?

Best,
Mallika Senthil

0 Kaushalya Satharasinghe 9 months ago in reply to Mallika Senthil

Prodigy 240 points

Hi Mallika, Since GND is floating below 24V by 3V3, both V+ and V- are at 3V3 with respect to GND. The 'C' node is below 24Vac from GND. I measured it and confirmed as well. There is no other precautions other than the 3V3 regulator. May be add some diode clamp may be better. What do you think?

Thanks,

Kaushalya

+1 Mallika Senthil 9 months ago in reply to Kaushalya Satharasinghe

TI__Expert 7880 points

Hi Kaushalya,

Yes a schottky diode would help keep the voltage at (Vin -) above GND. As long as the voltage at the input pins don't exceed abs max ratings, this solution should work.

Best,
Mallika Senthil

0 Kaushalya Satharasinghe 9 months ago in reply to Mallika Senthil

Prodigy 240 points

Hi Mallika,

Your help much appreciated.

Cheers,

Kaushalya

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INA180: Using for bidirectional current sensing