topic Re: USB hardware design Query in Kinetis Microcontrollers

USB hardware design Query

Embionics — Tue, 17 Jun 2014 05:47:33 GMT

Hello,

I am working with KL25Z64VFM4 controller for USB as a CDC device.

I have attached snap shot of USB schematic.

I have given external 3.3V from J4 connector as in the schematic.

And connected USB for testing as a CDC device.

It was working very well.

But when i am testing again i got the message from USB port that "Device is consuming more current".

After that i got that USB_5V and ground signal are short.

1) Is the attached schematic is OK for USB or do i need to make any changes in it?

2) Can I connect multilink for debugging when i am giving external 3.3V and USB is also connected?

Regards,

Amreen

Re: USB hardware design Query

apanecatl — Tue, 17 Jun 2014 18:11:53 GMT

I did not find any obvious problem in your schematic regarding the power rails however that does not rule out the possibility of a hardware failure.
Yes you can connect a debugging probe even though you supply the mcu with 3.3V VDD

Re: USB hardware design Query

galadragos — Tue, 17 Jun 2014 19:18:17 GMT

Put a capacitor of at least 1uF between USB_5V and ground.

It could also be a software issue, check that you are reporting the "correct" amount of current drawn.

Re: USB hardware design Query

Embionics — Sat, 21 Jun 2014 06:05:34 GMT

Hi Dragos,

Capacitor is there. I did not understand your point regarding software issue. Could you please elaborate more on this?I am using library component for USB CDC device.

Re: USB hardware design Query

galadragos — Thu, 03 Jul 2014 18:40:57 GMT

THe USB descriptors have a way of "setting" the amount of current the host should give to the slave device. Historically this field would have two values that represented 100mA and 500mA.

However, newer USB controllers can detect the amount of current the slave is consuming and will go into current protection mode if it tries to pull too much current.

Also, some drivers instinctively disable the USB port power for devices that request more than 500mA of current, in their headers, because that is what the maximum amount of current a slave device should draw from the USB port.