Question Regarding Pull down on Load Switch Enable

[jayalt]

I have an MCU GPIO acting as the control pin to a load switch enable. The load switch enable is active-high, and therefore majority of the time I have the GPIO pulled low on the MCU side, and will enable the GPIO when I want to turn on the rail.

I seem to have omitted a pull-down resistor on this particular rail. I’m a relative beginner, and I understand pull down/up resistors can help a pin always be in a defined state - I’m not so much concerned about this as my device is always on, and the MCU will always be controlling the pin.

However, I’m a bit confused on the current path now that the pull down resistor is gone. Am I at risk of damaging my load switch if I drive the enable pin directly at VDD with no external resistor? How can I figure this out if so?

[ataradov]

By drive directly to VDD you mean output high from the MCU? In this case there is no risk of damage. If you are driving a strong level from the MCU, then pull-up/down resistors are not doing anything. The goal of the resistor is to set a defined level while MCU is not actively driving the output.

But overall details may depend on the switch. The switch may not like to have intermediate/undefined level and you will have that while MCU is starting up, for example.

[joelaguirre92]

Hi jayalt

It s a good question because every time is important be carefully how we are using our MCU GPIO.

Almost MCU have pull-up outputs. I mean every time the outputs are ON. I would need know what kind of MCU are you using to confirm that. In addition you can configurate by software the kind of pin outs using a register bits.

If you are pulling up the MCU outputs you can connect this way.(MCU with pull up )
I have seen many circuits controlling MOCs circuits that way, but you need be carefully what is the max current your MCU can    R2 as looks in the picture, you should calculated. While MCU output is HIGH and EQUAL to V1 there are not current.

It would be nice if you share us some diagram or schematic about how are you plugin.


Hope you are well

 mcu with pull up.png (7.8 kB. 529x426 - viewed 44 times.) mcu with pull up.png