LPC5528 USB1_VBUS 5V tolerant?

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LPC5528 USB1_VBUS 5V tolerant?

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microcris
Contributor III

Hello

The LPC5528 datasheet states that this pin (pin 25 for LPC5528JBD64K) is 5V tolerant, but if I connect it directly to 5V, the LPC5528 gets really really hot and the USB connection gets lost. 
If I put a voltage divider in the USB1_VBUS, the connection is stable and there is no heat in the LPC5528.

 

I was connecting it like this:

microcris_1-1614793665774.png

microcris_3-1614793730519.png

So, is it really 5V tolerant?

Thank you for seeing this

1 Solution
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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Hello

If the USB_VBUS function is connected to the USB connector and the device is self-powered, the USB_VBUS pin must be protected for situations when VDD = 0 V.
If this is not the case with your application then I suggest you check the current supplied to the VBUS, a current that exceeds the ratings may be the cause of this heating.

If you have more questions do not hesitate to ask me.
Best regards,
Omar

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5 Replies
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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Hello

The pin is 5V tolerant only when VDD is applied at operating voltage level. I suggest you check the current of the pin, that current may be the cause of this heating.

Let me know if this is helpful, if you have more questions do not hesitate to ask me.
Best regards,
Omar

460 Views
frank_meyer
Senior Contributor II

> The pin is 5V tolerant only when VDD is applied at operating voltage level.

I am not sure if that is clear enough.

All operation conditions (like voltage) apply only in a powered state, i.e. VDD applied. In power-off state, any voltage on other pins beyond (usually) 0.3V will be harmful.

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microcris
Contributor III

It took me a little bit to get there but eventually I understood that @Omar_Anguiano  was saying the device needs to be fully operational (fully power supplied) in order to get the 5V tolerance in the mentioned pin.

I case the MCU power supply is not coming from the USB port (which is my case), I understand now that it is not possible to have a direct connection between the USB connector 5V pin and the USB1_VBUS pin without power supplying the entire MCU. I suppose that a 10kOhm resistor between those 2 pins will solve the problem.

Regarding the situation where the MCU is fully power supplied, I ordered more LPC5528 microcontrollers and I cannot confirm anything else until I receive them...
...BUT I'm almost certain that I had the device power supplied, I was seeing the "dmesg -w" output in the linux terminal and I was checking the mcu temperature with my finger. At some point the MCU got really hot and the USB connection got lost.

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Omar_Anguiano
NXP TechSupport
NXP TechSupport

Hello

If the USB_VBUS function is connected to the USB connector and the device is self-powered, the USB_VBUS pin must be protected for situations when VDD = 0 V.
If this is not the case with your application then I suggest you check the current supplied to the VBUS, a current that exceeds the ratings may be the cause of this heating.

If you have more questions do not hesitate to ask me.
Best regards,
Omar

View solution in original post

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microcris
Contributor III

"If the USB_VBUS function is connected to the USB connector and the device is self-powered, the USB_VBUS pin must be protected for situations when VDD = 0 V."

It is exactly the case. A self powered device and it gets really hot when VDD=0 and USB_VBUS is present. 

Thank you

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