# Combining voltage divider, pull-down resistor and low-pass filter in analog sensor signal

I am integrating a KP236N6165 analog absolute pressure sensor from Infineon. They recommend the following circuit :

My microprocessor which receives the signal uses 3.3V logic and is not 5V tolerant on its analog pins. I have therefore decided to use a voltage divider in my circuit bellow:

I have changed Infineon's R3 value from 22kOhms to 15kOhms (R36 in my schematic) as I have considered R6 and R7 from my circuit are in parallel and therefore formed an Req of 7kOhms (15+7=22). Is this assumption correct? Is my adaptation of Infineon's circuit, with a voltage divider, correct?

> Is this assumption correct?

No. The dividers (R6 and R7 in your schematic) will not limit the sensor output to ~3V. Those resistors are there to limit the minimum and the maximum output voltage, yes, but the values are wrong.

See section 2.6 on p.15 in the datasheet:

As you can see from the diagrams above, source currents of higher than 1 mA are not shown because it's outside the limits as shown under section 3.3 on p.19. Even if we assume that higher currents are allowed for a moment, to limit the max output voltage somewhere around 3V you'll need a very low pull-down resistance which can be a potential problem because of an excessive load on the IC's output.

EDIT: Apparently, the P5V in the OP's circuit is not the 5V power rail, it's the sensor's output.

Instead of using a divider + filter (i.e. 3 resistors), you can do the same thing with a divider and a capacitor:

simulate this circuit – Schematic created using CircuitLab

OUTx is the divided output which can be calculated from voltage division. For a maximum output voltage of ~4.9 V from the IC, it'll be somewhere around 3.27 V. The R67 is the Thevenin equivalent resistance of the divider, therefore the circuit will act as a voltage source with a series resistance. This resistance and the C1 will form a low-pass filter having a cut-off frequency of ~239 Hz.

• Thanks a lot for your answer Rohat. If I understand correctly, you would recommend that I remove the 15 kΩ resistor that I placed. The cut-off frequency of the filter will not be the same as in Infineon's schematic. In addition, is there a reason for which you prefer resistor values of 12kΩ and 22kΩ over those of 10kΩ and 20kΩ that I currently use? Commented Dec 10, 2023 at 13:49
• @Tommy95 you are taking the divider's input from P5V which is, I assume, 5V supply. My suggestion is to take it from the IC's output directly. Your divider from 5V will not do anything regarldess of the values. As for the values, you can pick whatever you want as long as the load current is within ±1 mA range. Commented Dec 10, 2023 at 14:14
• What I named P5V in my schematic is the pressure analog signal that comes out from the KP236N6165 sensor's Vout pin Commented Dec 10, 2023 at 15:25
• @Tommy95 you should have indicated that because a similar config is used in a reference circuit that you attached in your question. In that circuit the divider is taken from 5V, in your circuit it's taken from P5V which sounds like "Power 5V". Commented Dec 10, 2023 at 15:29
• Thanks a lot for your confirmations Rohat! Sorry for the misleading information, it was indeed "Pressure 5V range" that I meant by P5V Commented Dec 10, 2023 at 16:08