INA200: INA200 comparator not tripping

Dave Knight

Part Number: INA200

Regarding section 7.3.3 of datasheet:

What rise time is appropriate for a 5V reset?

The datasheet didn't specify, so I chose 1ms(seems wrong now). The CMPOUT pin floats at 2V on power up. Is this due to a bad rise time choice?

over 5 years ago

0 Patrick Simmons over 5 years ago

TI__Mastermind 21835 points

Hello Dave,

Thanks for considering TI in your design. The rise time should be some value within a few hundred nano-seconds to a few micro-seconds depending on your operating conditions. Is your supply also 5V? Do you have a pull-up resistor on the CMPOUT pin? If so, what resistance value are you using? If not, you need to put one on your CMPOUT pin and tie it to the supply.

0 Dave Knight over 5 years ago in reply to Patrick Simmons

Intellectual 590 points

Patrick,

10k pull on on CMPOUT and RESET pins to 5V.

I want the CMPIN to move slowly. Are there requirements for rise time of CMPIN as well?

Regards,

Dave

0 kai klaas69 over 5 years ago in reply to Dave Knight

Guru 140200 points

Hi Dave,

I don't think that it's wise to have such a high filter time constant at the comparator input. Datasheet has no cap at all at the comparator input.

The /RESET time constant is also massively too high.

Kai

0 Patrick Simmons over 5 years ago in reply to kai klaas69

TI__Mastermind 21835 points

As Kai pointed out, your RC constants could be the culprit. Below I did some calculations based off of the values I see in your schematic and I chose arbitrary initial and final voltage values across your caps. Could you by chance verify with oscilloscope shots that you are getting similar rise times on your RESET, CMPOUT, CMPIN pins?

Hello Dave

0 Patrick Simmons over 5 years ago in reply to Patrick Simmons

TI__Mastermind 21835 points

Hello Dave,

I ran some tests on my end to see if I could get any peculiar behavior on the CMPOUT pin. Below are the setups I used. Although they do not match your exact setup they may help guide you to what is happening with your device. For each of these I actually slowly dialed up the Vin voltage (0.1V increments to 12V over the course of 30 seconds). From that I found that for cases 2-4 the CMPOUT trails roughly 0.2V behind Vin. However for case 1, CMPOUT trailed Vin up to 1.1V and thereupon it dropped to about 65mV which then more slowly increased with Vin. Please let me know if you have any further questions or if you have made any progress in your debug.