I am trying to monitor a 12 volt power rail and need a reset signal to be asserted when the system loses power. I need the reset singal to be asserted at no lower than 9.7 volts in all corner cases (assuming 1% accurate exernal resistors).
What is the recommended resistor values in the voltage divider to scale down the 12 volt rail to have a balance between accuracy and low current?
What is the maxium voltage a reset signal could be asserted at, given the reistor values determined above?
Can you please help me determine the above for both a TLV809 and a TPS3808
Below is an application note that discusses the design considerations for the resistor divider. Basically, the current through the divider should be at least be 100x the leakage current into the device. This will yield the optimum accuracy for the least amount of current through the divider. This app note also discusses the accuracy of the SVS when the tolerance of the resistors is included.
For the pull-up resistor at the RESET output of the SVS, if there is no design requirements in the datasheet, the RESET voltage can be pulled up as high as the abs max rating of the RESET pin. However, it should be pulled up less than this so as to prevent damage to the device.
Please let me know if this helps.
Thank you for the help. I wanted to add some of the offline help you provided me to benefit others.
Sources of inaccuracy
The team identified three sources of inaccuracy for circuit there are as follows:
Proposed circuit and accuracy
Using the app note highlighted above as a guide we formulated a voltage divider that should draw 100 times the leakage current of the device to optimize the power vs. accuracy curve. Assuming a requirement to use E96 1% accurate resistors, below are the recommended resistor values to use:
Using the above resistors the team calculated the minimum voltage a reset would happen, maximum voltage, and nominal voltage that would trigger a reset considering all three sources of inaccuracy above. These are highlighted in the table below.
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