No power button needed

Hello all

we have a product which will not need a power button.

What is a bare minimal design approach for this?

Looking at the timing diagram there is no need for delays on setting EN high

image

Can POWER_EN just be tied to the VDD_IN supply and then use the SYS_RESET output signal to enable the carrier board supplies?

This would eliminate a lot of complexity and reduce build cost.

can anybody comment?

Hi, the POWER_EN should be high after VDD_IN is stable. The timing is about ~80ms. You can refer to the Power ON/OFF Logic design of P3449 schematic as below for auto-power-on design.

are you simply using the 412k and 2.2uF to create a very slow RC combination, (with time constant 0.9seconds) ?

I wont have a reset or power button on the product, so can i omit these?

The RC is also necessary for auto-power-on to let VDD_IN in stable first and then pull power_en high.

hi Trumany

yes I understansd that part…

I dont need a reset or power button, so can i completely eliminate this part?

And just tie the left side of the 412k resistor to VDD_IN ?

It should be ok in theory, but has not been validated yet.

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