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Part Number: INA301-Q1
The customer is using INA301A3-Q1.Gain=100. His load current is 5mA. And he use 3.3V power supply. His Rsense is set to 200 mohm.
Please check his schematic in the fig 1. His issue is the ALERT pin always outputs the low level.
I also do a TINA circuit and do a transient with the zero initial values condition. Please check the fig 2 and fig 3.
For the customer's issue, would you provide some suggestions and send me a correct TINA circuit?
Best Wishes, Mickey Zhang Asia Customer Support Center Texas Instruments
Interestingly my model with your conditions does not pull the ALERT low until IG3 crosses ~10mA. On that note, there seems to be a discrepancy between your graph and your TINA schematic. Why is your graph value approaching 6 and not 6m? Below is a screen shot of my circuit and outputs. Is your DC Level on the current generator set to 0?
Patrick Simmons, TI Sensing Products Applications Support
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In reply to Patrick Simmons:
Hi Patrick, Thanks for your help. I ignore the DC level for the IG3. Q1: Would you upload your TINA circuit model? And I would like to get the setting of your IG1, include the DC level, the amplitude and the frequency of the signal waveform. I also would like to get if you use a transient with the zero initial values condition. Q2: The customer's load current is 5mA. So I have changed my TINA circuit. I use a square wave from 0 to 5mA for the IG1. But the Alert pin is the low level only from 0 to 50us in the simulation result, it is always the high level in other time. I use the transient with the zero initial values condition. Please check the attach. If the input current is reached to 5mA while the Alert is the high level, I know this is incorrect. I would like to get why the Alert waveform is not the square wave, that is the Alert waveform should be changed with the input current waveform. Would you send me a correct circuit for the square wave input current that the amplitude is from 0 to 5mA，like my IG1 setting?
In reply to Mickey Zhang:
Below should be my TINA file. When I do transient analysis using “initial conditions” or “zero initial conditions,” I get a graph similar to yours in which the alert pin starts low and then goes high after 50us. This appears to be a startup condition for the device model. In reality startup for the internal comparator could potentially complete sooner, however this is something I would need to verify in the lab. As for the alert pin remaining high, this could be a combination of model characteristics including voltage offset, comparator voltage offset, and noise. It also could be that the model was not properly set up for the lower current measurements where we actually expect to see the greatest amount of error in accuracy. So far I have noticed in the model that if the RLimit resistor is too small the alert function completely breaks. So, I will need to test this in lab. Since we do not currently have in stock at our location the A3, 100 gain option, this may take a few days. I will let you know when I am able to measure this in the lab.
I did some tests in the lab and I do believe you can get the device to have the ALERT trip around 5mA through the shunt resistor as long as you do not need high accuracy. For my setup, I had a 200mohm 1% shunt and 1238.8 ohm (measured) limit resistor. For this setup my common mode was 0V. (I do plan on repeating with 5V common mode later.)
What I observed from this was the device triggered at a Vout of 0.0924V. Ideally the value should have been 0.099104V. This discrepency although large, is in agreement with the datasheet. As just the max contribution of error from the amplifier Vos and the comparator Vos can be as high as 8mV. Ultimately other sources of error such as gain error and resistor tolerance can also contribute to the overall error.
Another thing you will need to consider if you decide to proceed with this option is that the comparator has hysteresis. Therefore, resetting the alert at such a low threshold may be difficult, even when the device is in transparent mode. However, one possible solution you could try if it is available to you is to temporarily bump up the limit pin voltage. This will help reset the ALERT status.
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