USB disconnect detection: VREGIN staying high

[vincentg_]

Hi all,

i ran into a problem to detect the disconnect of USB on a MK22FN512. 

VREGIN is connected to the output of an external 3.3V voltage regulator (NCP502SQ33T2G). I'm checking the state of that connection over a voltage divider to stay under my 1.8V Supply. The measuring pin is configured as input, no pull.

The reason for not taking the enable pin of the external regulator is that the voltage on this pin may be alot higher.

If I disable the voltage regulator the output goes down to about 2.3 volt and stays there instead of going to 0. If i short it the signal goes low and stays low.

I tried adding a pulldown to empty the output capacitor of the regulator but it doesn't help, so there must be some kind of leakage somewhere.

Could there be any feedback from the VREGIN pin? 

Any hints would be great.

Happy Holidays

Vincent

[xiangjun_rong]

Hi, Vincent,

Regarding your issue, I am not very clear about your issue. I see that you connect the external regulator NCP502SQ33T2G output to VREGIN pin, and connect the VOUT33 with a 2.2uF cap. I suppose you have connected a capacitor to the VREGIN pin for example 10uF cap. If you test the voltage of the VREGIN pin and VOUT33 after you enable the internal regulator or disable the internal regulator by controlling the SIM_SOPT1 reg, what is the result? which pin is 1.8V as you said?

BR

Xiangjun Rong

[yinni]

Hi Xiangjun,

I have the same problem as Vincent. 

I tried to use a GPIO of MK50 to detect the logic level at VBUS which is connected to VREGIN, my thought was:

• GPIO reads LOW if no USB connection, and my system operates under data collection mode (data saved to SD card)
• GPIO reads HIGH with USB connection, and my system operates as a USB device so that data can be transferred to a USB host

But my GPIO always reads HIGH because VREGIN stays always stays HIGH:

• No USB connection and USB voltage regulator disabled, 2.9V measured at VREGIN
• No USB connection and USB voltage regulator enabled, 3.28V measured at VREGIN
• With USB connection and USB voltage regulator enabled, 5V measured at VREGIN

How can I solve this problem?

Many thanks in advance!