I am working on the motor controller interface board with a 48 V battery connected (58 V max), the board should remain OFF (no 12V should be generated) when battery is plugged-in, until the user taps a momentary pushbutton (SW1 to GND). A short press should enable the buck (LM5164) by pulling EN_BUCK line. This EN_BUCK line should remain high even after the pushbutton is released.

When idle, the MCU pulls BUCK_SHUTDOWN low to turn the buck off and minimize standby drain i.e 12V OFF -> 5V OFF -> 3.3V OFF (MCU and other peripherals off). To Turn on the supply again, User will have to press the pushbutton again. After boot, the EN_BUCK line should remain High(buck enabled) even after the button is released.

SW1 is a momentary to GND that nudges EN_BUCK > EN/UVLO threshold. A diode/zener network clamps EN below 6 V. There is no alternate power source.

The Circuit isn't working as expected. Am I doing anything wrong? When I plug-in the battery, the Buck converter is immediately turned ON no matter if I press the switch or not. My intent was a simple “OR” of two sources into the buck’s EN pin:

1. a momentary button pulse to start.
2. an MCU HOLD to keep EN high.

Also, I have some questions-

1. What type and rating of fuse would you recommend here (fast vs slow-blow, current value)?
2. Do I need to add bulk capacitor (electrolytic) at input and output of buck converter?
3. Standby / control-network current - Is my EN clamp/divider likely drawing unnecessary current at 58 V (e.g., zener sink through a low-value divider)? What’s a sensible target for standby draw (µA–mA) for this kind of design, and how should I bias EN to achieve it?

I want the board OFF at battery plug-in to avoid standby drain and MCU can shutdown the whole board to avoid battery drain when idle.

I’m open to moving the eFuse or Hot swap controller if that's the right approach. BOM cost is not an issue reliability is important.