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I have a high-side MOSFET driver (MAX1614) that is used to power a device on and off. The /ON and /OFF pins of MAX1614 are connected to PCA9536 I2C-GPIO expander. The goal is to use a physical button connected between the ON and GND to power on the device and then use uC to power the device off when required.

MAX1614 contains weak pull-up current sources connected to /ON and /OFF pins internally. If I power PCA9536 via an external source, things work like a charm. However, when PCA9536 is left unpowered (as it should be when device is not working), it loads the ON and OFF pins in a way that they both are at 0.28V. This is read as low on both /ON and /OFF and the device does not power on when pulling /ON low via the push button.

At the moment I'm thinking about just using two resistive dividers (47K/10K, Vbatt=22V) to pull the /ON and /OFF to logic high. This seems to work and I can tolerate the power loss in the divider. Are there any smarter options (Resistor + Zener)?

Edit: Schematics, External button to GND is connected between Pins 4 and 5 in the right-most connector. High-side MOSFET control

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  • \$\begingroup\$ Please add a clear circuit diagram for your particular application. It would help us a lot to understand your problem \$\endgroup\$
    – Daniel Melendrez
    Oct 1, 2022 at 21:27
  • \$\begingroup\$ What about just a weak pull down resistor? Is that OK for your application? \$\endgroup\$
    – winny
    Oct 3, 2022 at 10:24
  • \$\begingroup\$ I need /ON and /OFF to be logic high with nothing but the BATT connected. The weak pull-ups in MAX1614 are not strong enough and unpowered IO expander is pulling them down to undefined state. \$\endgroup\$
    – jpou
    Oct 3, 2022 at 11:42

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