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I am trying to get a MAX809S IC to work with a 24 V supply. The MAX should trigger at around 2.93 V at its VCC pin and turn the RESET pin high. Because the MAX is only rated at max. 6 V at the VCC pin I created a voltage divider with a 2k and 510Ω resistor. Sadly the MAX is not switching the RESET pin. It is working perfectly fine if i provide a 0-5 V supply directly to the VCC pin. The voltage divider is capable of delivering almost 10 mA. This should be more than enough to power it. What am I doing wrong? The MAX should turn on/off at around 15V but it does nothing. I can not lower the resistor values anymore because they will overheat then. enter image description here

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  • \$\begingroup\$ Please add a link to the device's data sheet. \$\endgroup\$
    – Andy aka
    Commented Oct 6, 2023 at 13:12
  • \$\begingroup\$ I found a datasheet MAX803-MAX810Z.pdf. Maximum supply current is shown as 100 µA. \$\endgroup\$ Commented Oct 6, 2023 at 13:17
  • \$\begingroup\$ I am referring to this datasheet: onsemi.com/pdf/datasheet/max809s-d.pdf There it says maximum input current 20mA and supply current max 2.5µA \$\endgroup\$ Commented Oct 6, 2023 at 13:20
  • \$\begingroup\$ Remove C2 and R3 and just measure the voltage on pin 2. \$\endgroup\$ Commented Oct 6, 2023 at 13:33
  • \$\begingroup\$ Which MAX809S are you using? These are available in a number of reset thresholds \$\endgroup\$
    – user28910
    Commented Oct 6, 2023 at 13:39

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Thx @Spehro Pefhany. It was in fact the 47nF (C2) capacitor that caused the problem. I dont know exactly why but at least it is working now. C1 or R3 did not cause any problems.

EDIT: I also changed R1 and R2 to a 50k potentiometer which also works. With a 100k potentiometer it stopped working though.

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    \$\begingroup\$ FullMetalJack - Hi, Just a bit of feedback: While you can write (and, after 48 hrs, áccept) your own answer, you found the solution through a comment from someone else, so it would be polite to first reply in a comment to that person, inviting them to write an answer. || You seem to have tried to reply in an answer using @username but that only triggers a notification from a comment since answers are not supposed to address people, but just to be the solution. || I will add a comment and invite that user to write an answer (it's their choice whether or not to do so). Thanks. \$\endgroup\$
    – SamGibson
    Commented Oct 6, 2023 at 14:04

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