Analog Input Current

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Doughty
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Last seen: 2 years 2 months ago
Joined: 2020-07-09 18:22
Analog Input Current

Hello,

I am trying to monitor a 5V signal with a comparator on my SLG46826G which is powered at 3.3V.  I have a series 10k to keep the input current below the 1mA-max spec. and had initially used an internal, 10k pulldown on the SLG to bring the voltage to ~2.5V.  However, the measured voltage at the pin is ~1.0V and only rises to 1.5V when I changed the external resistor to 5.1k.  Subsequently, I tried configuring the input pin to 'floating' but didn't notice much change.  The voltage is where I would expect it to be in the simulation, but on actual hardware, it's much lower.  Input currents should be negligable per my read of the datasheet.  Any idea what could be going on here?  Screen grabs of the configuration are attached.

Thanks!

Chris

Attachment: 
Device: 
Device Number: 
SLG46826G
olehs
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Last seen: 1 year 7 months ago
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Joined: 2018-02-07 11:40
Doughty, 

Doughty, 

Thank you for your question!

I've made the testing and found the voltage divider works as it should work when using the internal 10k pull-down resistor. Please see the schematic I used during the testing there also is the waveform attached.  I believe this issue could have a few reasons:

1. There are additional resistors in the circuits, which influence on the divider's coefficient.

2. Please check the resistor value

3. The voltage source has a huge voltage drop. Could you check the input voltage, which goes to the divider? It should be 5V.

4. There could be some variation in the internal pull-down resistor. Typically it is 10k, but the variation is from 6.32k to 13.5k. So the worst-case 6.32k can show similar behavior. 

Please let me know if you found the problem or my advice helped you to fix it. 

 

Best regards, 

olehs

 

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Doughty
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Last seen: 2 years 2 months ago
Joined: 2020-07-09 18:22
Olehs,

Olehs,

Thank you for checking this so quickly, confirming operation, and the thorough documentation!  After additional review, I have found the problem on my target PCB.

Chris

olehs
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Last seen: 1 year 7 months ago
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Joined: 2018-02-07 11:40
Doughty,

Doughty,

It's great to hear that you found where the issue was.

Please let me know if you have any further questions about the GreenPAK and I will help you to answer.

Best regards,

Oleh Sapiha