Identify 3 states at the input - Automotive circuit 24V system [duplicate]

Question

I have a requirement to build a circuit which can identify 3 states at the input and the output is given to ADC of uC. I have the below circuit for 12 V systems:

The input can be connected to gnd, battery(T87) or left open. I am trying to use the same circuit for 24V system but since the ISO pulses(have to consider ISO pulses since input can be connected to battery) would go up to +- 600V in the 24V system, what are the changes that I will have to make. I have to probably change the resistor values and packages. What about the diode ? what are the parameters that I have to consider for diode selection ? and what would be the worst case for the diode, for example like Jump start, load dump , ISO pulses, reverse polarity ? the switching diode BAW56W was chosen for 12V system because it was already available in the BOM of our product.

Here is the link to my other related question, I was not too clear while asking that question. My main requirement is that my circuit differentiate between 3 states Automotive electronic circuit design, Voltage divider to uC ADC pin

Answer 1

I suggest a circuit like this: R46 limits the current into Zener D5. For 24V, that current would be (24-5.6)/1000=18.4mA. Adjust values as desired.

R44 limits current into the ADC to protect against any transients.

I forgot the diode for reverse polarity protection. R46 in series with the diode should protect it from excess current.

R121B1 and R121B2 can be higher, eg 100K. Higher impedances will be more susceptible to EMI.

Please remember to mark as answer if this solves your issue.

Values are only guesses. You'll need to do the math to make sure it hits the voltages you want. Specifically R46 forms a voltage divider with R121B2 when pulling to ground, and R121B1 when pulling to 12/24V. Make sure to set D5 to a voltage range your ADC can handle.