INA200: INA200 comparator not tripping

Dave Knight

Part Number: INA200

To whom it may concern,

This is for automated test equipement.

I want to use INA200 to monitor current of DUT(device under test), and disconnect(by relay) the DUT from circuit if current draw exceeds 20mA, and also turn on a red LED as a visual indicator that an overcurrent event has occured and the DUT should be replaced. A switch is used to reset the latch on the INA200 to turn the relay on so testing can resume after a new DUT is connected.

The circuit does not work as intended. CMPOUT does not go low when CMPIN > 600mV. I've seen CMPIN go as high as 1V without CMPOUT going low. Conversely, CMPOUT does trip when COMPIN is 0V. The polarity of COMPOUT seems to be opposite of what I expect it to be. Am I missing something? How do I accomplish what I want with this circuit?

over 7 years ago

0 Jason Bridgmon over 7 years ago

TI__Genius 14825 points

Dave,

This is the basic behavior of the CMPout vs CMPin pin from the data sheet, is it not what you expected:

Also I see you have a 12V supply and a 5V reset. There is a known behavior when the voltages are different, as mentioned in 7.3.3 in the data sheet:

When Vs and RESET are different, TI recommends adding a low-pass filter (LPF) on the RESET pin to avoid comparator behavior inconsistent with the data sheet. For instance, with a 12-V supply and a 3.3-V RESET, a rise time of 400 ns is appropriate. Similarly, with an 18-V supply and a 2.7-V RESET, a 1-µs rise time is appropriate; see Figure 31.

I don't see an option for a low pass filter in your schematic on RESET, so perhaps if you are using reset with a fast rising edge, you could be creating some odd behaviors. Your thoughts?

0 Dave Knight over 7 years ago in reply to Jason Bridgmon

Intellectual 590 points

I had the output polarity backwards in my head. Thanks for clearing that up, and also for reminding me about the RC on the REST pin.

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INA200: INA200 comparator not tripping