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I am using an Infineon ITS4200S-SJ-D highside switch to control power to a resistive load. Internally the part is basically a PFET with some additional features.

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I have a 10k pulldown on pin 2, +12V on pin 5, and a 100ohm resistive load on pin 3.

Everything works great except I notice that if I connect the load and the +12V before I connect the GND I get a leakage current to the load.

I know that the simple answer is "always connect the GND cable first." But I'm wondering if someone can give me an idea for a simple circuit that I can add to prevent this leakage and keep the load totally un-powered until both of the power supply cables are connected correctly and I activate the input at pin 2.

Here is the schematic. for troubleshooting I have disconnected the microcontroller activation line as indicated by the little red X. The problem I'm trying to solve is when the +12V cable is connected and the GND cable is unconnected I see about 15mA through the load.

enter image description here

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  • \$\begingroup\$ Pretty hard to do that. From what I understand the command ground is not the same as load ground. You should give more details about the circuit. A pull up/down on the IN and some supply to IC gnd from load gnd might work but you need to be more specific. \$\endgroup\$ – Dorian Apr 26 '18 at 8:18
  • \$\begingroup\$ Why is everyone calling it a PFET? The datasheet (and the internal schematic) clearly show it as an NMOS device. \$\endgroup\$ – Dave Tweed Apr 28 '18 at 0:06
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If you cannot fix the proper connection sequence, then the dual Pfet solution used on common battery management designs is needed.

Because of ESD protection diodes on some protected switches, leakage current will exist.

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Usually Low side switching is preferred, but here is an unprotected high side series complementary switch.

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Vgs must be protected in automotive applications for 40V (?) Joule load dumps and reverse 24V so Low side switches are often preferred.

We do not know your other requirements besides leakage.

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  • \$\begingroup\$ This answer is not helpful at all. Thus, downvoting. Maybe elabarote on the "dual Pfet solution used on common battery management designs"? \$\endgroup\$ – user94729 Apr 26 '18 at 4:25
  • \$\begingroup\$ Thanks for your feedback. google.com/… It is really common to use 2 FETS as a bidirectional switch to stop the flow of current \$\endgroup\$ – Sunnyskyguy EE75 Apr 26 '18 at 7:12
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    \$\begingroup\$ I always try to put in more effort in my answers than the OP does with the question. Hence such a short answer to lead you to a better question. \$\endgroup\$ – Sunnyskyguy EE75 Apr 26 '18 at 15:53
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    \$\begingroup\$ Basically a series switch disables the load until the output is active .i.e. Vdd and Vss are connected but you need to specify all our requirements to find the best solution... surge dump, reverse voltage, power sequence, current etc. Hot Swap etc. i.e. not just describe this problem but what the solution needs to be protected against. and function for. (purpose) Otherwise the IC cannot be used in this instance. \$\endgroup\$ – Sunnyskyguy EE75 Apr 26 '18 at 16:02
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    \$\begingroup\$ Removed -1 after the edit. \$\endgroup\$ – user94729 Apr 27 '18 at 4:49
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This is an Integrated Circuit, meaning that a lot of smart components are integrated within, including logic and ESD protective rings etc. etc. When dealing with integrated circuits, you don't arbitrary connect pins to live voltage, so simple rules of electricians do not apply. You connect the IC in accord with manufacturer's specifications, to your cables, and then apply power. Otherwise anything can happen, like unwanted triac-latch effect that shorts everything and smokes your circuit.

If you really need a "hot plug" capability, your connectors must be designed/selected to connect ground first, power next, and the rest after.

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  • \$\begingroup\$ Thanks for the reply. I have considered a connector solution but unfortunately the connectors are part of an existing system and cannot be changed. I understand that without intimate knowledge of the internal working of the IC I cannot predict how different power connections will affect the circuit. What I'm looking for is an external circuit that I can add in that will handle improper power connections actually reach the IC. \$\endgroup\$ – Sidearm Apr 26 '18 at 15:52
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You can try a resistor from output pin to GND pin. Since the current consumption in stand by is 15uA this will bring the IC into the normal working voltage where it can completly turn off the pfet. When active the resistor will add to the load. Try something above 1kohm.

schematic

simulate this circuit – Schematic created using CircuitLab

All voltages are relative to bat1 GND

R3 is added to fix the floating chip GND

If the leakage current is 15mA then Vout is RL x 0.015 = 1.5V

If U1 is sinking the max current of 2mA then chip GND will be at 1.5V + R3 x 0.002 = 3.5V

That leaves 12 - 3.5 = 8.5V VS to chip GND enough for the chip logic to work in parameters and close the PFET properly.

After the PFET is closed the leakage current through the load will go down to the standby current of the chip, 15uA, OUT voltage to 0.1mV, chip GND voltage to 0.1mV + R3 x 15uA = 15.1mV

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