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I’m using two AP2301B MOSFETs in a back-to-back config to switch between battery (BATT+) and USB 5V. The gate is controlled via a 100k pull-up and 100k to GND.
Attached: Oscilloscope capture



Schematic


Issue: When battery voltage is around 3.7V, I see a voltage dip (~2.2V drop) on VCC during switching. This resets my MCU. But when battery voltage is above 4V, the dip is gone or negligible.

Questions:

Why does the drop only happen at lower battery voltages?

Is it due to MOSFET body diode or slow gate transition?

How can I make switching smoother and prevent MCU reset?

 

Try removing Q5; BATT goes directly to Q6.

 

Try removing Q5; BATT goes directly to Q6.

Why removing Q5 why not Q6?
How does this affect reverse current and control logic?

https://electronics.stackexchange.c...on-switching-between-battery-and-power-supply
https://ww1.microchip.com/downloads/en/AppNotes/01149c.pdf

In this post they have used q5. So whhy to use q6 over q5?

 

If you are going to remove a FET, I would thing Q6 is the one to go. Otherwise, with Q5 gone, the +5V will feed the battery via the Q6 body diode.

 

These are enhancement-mode MOSFETs. They are turned on when G is applied a negative bias wrt S. The current flows from S to D. Q6 is on when +5V supply becomes 0v, as its G is negatively biased wrt S. For Q5, mainly the internal diode passes the current, which explains the drop of the output voltage.

 

These are enhancement-mode MOSFETs. They are turned on when G is applied a negative bias wrt S. The current flows from S to D. Q6 is on when +5V supply becomes 0v, as its G is negatively biased wrt S. For Q5, mainly the internal diode passes the current, which explains the drop of the output voltage.

If you are going to remove a FET, I would thing Q6 is the one to go. Otherwise, with Q5 gone, the +5V will feed the battery via the Q6 body diode.

These are enhancement-mode MOSFETs. They are turned on when G is applied a negative bias wrt S. The current flows from S to D. Q6 is on when +5V supply becomes 0v, as its G is negatively biased wrt S. For Q5, mainly the internal diode passes the current, which explains the drop of the output voltage.

These are enhancement-mode MOSFETs. They are turned on when G is applied a negative bias wrt S. The current flows from S to D. Q6 is on when +5V supply becomes 0v, as its G is negatively biased wrt S. For Q5, mainly the internal diode passes the current, which explains the drop of the output voltage.

i tried removing both the q5 and q6 ,

the result i found:
when i removed the q6 it worked without being reset but the switching time is much higher.

and when i removed the q5 it wont ,the mpu gets reset again the same problem.

 

If you are going to remove a FET, I would thing Q6 is the one to go. Otherwise, with Q5 gone, the +5V will feed the battery via the Q6 body diode.

i tried removing both the q5 and q6 ,

the result i found:
when i removed the q6 it worked without being reset but the switching time is much higher.

and when i removed the q5 it wont ,the mpu gets reset again the same problem.