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a friend of mine developed this Schematic and Circuit.

The Problem is, on LIN_BUS (please ignore the Name) should be KL15 Volage (13.8V) if the FET switches.

enter image description here

But if FET1_CNTRL is LOW (0.0V) the Output Voltage @ LIN_BUS is 800mV

If FET1_CNTRL is HIGH (3.3V) the Output Voltage @ LIN_BUS is 800mV

Here is my MCU Config:

enter image description here

Here is my Code and the Voltage on the BSS123.

 HAL_GPIO_WritePin(FET1_CNTL_GPIO_Port, FET1_CNTL_Pin, RESET); // = 13.6V 0V @ D-BSS123
    //HAL_GPIO_WritePin(FET1_CNTL_GPIO_Port, FET1_CNTL_Pin, SET); // = 13.6V 3.3V @ D-BSS123

Very strange. Does anybody have a suggest what is faulty here?

If 3.3V on BSS123 the Gate on IRF9362PBF is 0.0V If 0.0V on BSS123 the Gate on IRF9362PBF is 13.2V

Edit:

Added some Load. Got a meassurment fail yesterday. So Drain on IRF9362PbF is allways 800mV. Anyway in which state BSS123 is.

I added 5V / 12V / GND directly to the Gate from IRF9362PbF, but still no changes on Drain side. Tested with different hardware but same result.

I reversed the Tips from the Measurement Tool and connected the GND Cable to the Drain. and the Plus Cable to Vss.

Now I measure +13.8V But in both BSS123 States.

Checked with different Hardware. But same result.

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    \$\begingroup\$ Have you measured the gate voltage on the P-FETs in both states? \$\endgroup\$
    – user16324
    Commented Sep 21, 2020 at 16:16
  • \$\begingroup\$ Are you sure all the connections are correct? \$\endgroup\$
    – Pangus
    Commented Sep 21, 2020 at 16:27
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    \$\begingroup\$ Is there any sort of load on LIN_BUS? \$\endgroup\$
    – marcelm
    Commented Sep 21, 2020 at 16:42
  • 1
    \$\begingroup\$ No, no other stuff. \$\endgroup\$
    – vt1111
    Commented Sep 21, 2020 at 16:43
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    \$\begingroup\$ You shouldn't expect it to do much of anything without some sort of load. Toss a resistor to ground on there to draw some current for test purposes. \$\endgroup\$
    – Chris Stratton
    Commented Sep 21, 2020 at 16:51

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