INA280: Device Operation when Reverse Current Flows

Shinichi Inoue

Guru 20671 points

Part Number: INA280

Dear Specialists,

My customer is considering INA280 and has a question.

I would be grateful if you could advise.

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This is a question regarding the TI device INA280A series.

I understand that the INA280 is a unidirectional current sense amplifier.

Could you please let me know what happens to the output when reverse current flows.

For example,
・0V (0A) output
・Undefined output

There was no plan to have the current flow in the opposite direction.

It is found a slight reverse current flows due to the capacitor and inductor on the load side.

At this time, I would like to confirm whether the detection circuit (control circuit) does not malfunction.

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I appreciate your great help in advance.

Best regards,

Shinichi

over 1 year ago

0 Peter Iliya over 1 year ago

TI__Mastermind 31735 points

Hello Appreciated Engineer Shinichi,

I am looking this over and will respond shortly.

Best,

Peter

+1 Peter Iliya over 1 year ago in reply to Peter Iliya

TI__Mastermind 31735 points

Hey Shinichi,

The output will just saturate into the ground rail. There is no phase and polarity reversal from negative overdrive.

The only thing that will change is device delay time coming out of 0V. The more negative the shunt voltage is, the longer it will take Vout to get out of saturation and into linear operation.

Sincerely,

Peter

0 Shinichi Inoue over 1 year ago in reply to Peter Iliya

Guru 20671 points

Hi Peter,

Thank you for your reply.

I understand the output will saturate into ground rail.

Could you please advise one more question?

Are there any timing spec of recovery time from saturation.

I appreciate your great help and cooperation.

Best regards,

Shinichi

+1 Peter Iliya over 1 year ago in reply to Shinichi Inoue

TI__Mastermind 31735 points

Hey Shinichi,

Since this behavior is not tightly controlled there is no specification. However, based upon testing we have done, it seems like the overload recovery delay may only last up to 80 µs assuming a -70mV input. I would say that you would need to allow for about 100µs of delay time, but it should be tested with several devices in your system and adding +20% margin to the max value.

Here are some ways to avoid this delay:

1. Use a bidirectional device (e.g., INA296) and supply a ~100mV input reference voltage. Use ADC to read the VREF to obtain differential output measurement or use precise VREF source.

2. With the INA280, insert a small resistor at IN- pin which will generate a small input offset voltage (Rin-*IB) that will bias Vout into linear region when lood <=0 A. Doing this will probably require a one-point calibration to negate variation in IB and Rin.