Kinetis K60 - USBDCD module query

[kaitav]

Hi,

We are using Kinetis K60 MCU in on of our designs and we have implemented USB FS device functionality. The USB port is intended for both powering the product as well communicating with PC. We also intend to power the product using a USB battery pack/ USB power bank. However, our system does NOT use any kind of re-chargeable/non-chargeable battery, hence does NOT have any external battery charging IC/module. It does NOT have any separate communication module as indicated in the USBDCD section of K60's reference manual.

Can we still use the USBDCD module for the following:

- To detect with what is our product connected: PC/Laptop OR USB power bank

- If connected to PC/Laptop, facilitate enumeration and drawing up to 500mA from the USB host

- If connected to USB power bank, no need for enumeration BUT inform the device firmware that it is connected to a USB power bank and hence can draw power higher than 100mA without enumeration

Would it be possible?

Please let me know if anything is unclear in my description.

Thank you so much in advance for any suggestions/help.

Message was edited by: Kaitav Sapre Made the question explanation simpler.

[kaitav]

Anyone please?

[kaitav]

Could anyone please help me with this question?

Thanks!

[Jorge_Gonzalez]

Hello Kaitav Sapre:

From your description it sounds like you do not have any kind of current limiting IC to control the current drawn from the USB port. If that is the case then the current will entirely depend on your board's circuit (hardware).

The only difference with connecting to a PC or to the battery pack is that according to USB specification the USB device descriptor needs to report that the device is "Bus powered" and how much current it needs from the bus (Max 500 mA, unless it is a charging Host port); while in the battery pack case your product will simply draw power without reporting anything. I don't think you need the USBDCD module in your case.

Please let me know if I misunderstood your question.

Regards!,
Jorge Gonzalez

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[kaitav]

Hi Jorge,

Thanks for your reply.

Yes, we do not have any current limiting element in our board. Is it really recommended for a USB device port?

Yes, but the issue is we are deciding on the "enumeration" right now, whether 100mA or up to 500mA current is available and accordingly power on the product. Since with USB power bank enumeration won't happen, we won't be able to detect if the product has been connected to a USB power bank and power the entire product. Our design is such that we enable the power to other boards after the first board housing USB port gets the power and enumerates.

That is why we need some detection mechanism that can help us identify the type of host (PC or Power bank) with which our product is connected and accordingly inform the firmware so that the entire product can be powered in any situation. And I thought USBDCD module could be helpful for this.

I hope this makes it clear.

Looking forward to your help.

Thanks,

Kaitav

[kaitav]

Hi Jorge,

I am awaiting your reply.

Thanks,

Kaitav Sapre

[Jorge_Gonzalez · Accepted solution]

Hello Kaitav Sapre

Sorry for the delay.

The USBDCD is intended to be used with rechargeable battery powered systems and your case does not match the target application. Since you do not have a dedicated battery charging IC to regulate the power drawn from VBUS, then your system will not meet the maximum 2.5 mA initial condition:

This condition should also be maintained during charging port detection:

I am sorry for this inconvenience.

Regards!

Jorge Gonzalez

[kaitav]

Hi Jorge,

No worries, I understand.

Thanks for your concise reply. That's unfortunate to know that we cannot make use of USBDCD module for our application. Just a few last questions before closing this topic:

1. Could you please suggest some battery charging ICs that can work with the K60 USBDCD module? Is something like this good? - http://www.ti.com/lit/ds/symlink/bq24230.pdf

2. If we manage to design in the battery charging IC on our board, we would still need the "rechargeable batter" for the USBDCD module to work, right?

Thanks again for your support.

[Jorge_Gonzalez]

Hi Kaitav:

1) Yes, that IC should work. Actually any battery charging IC supporting a USB input and controllable current should work, with the condition of having a matching communication interface with the Kinetis part (typically I2C, UART or simple digital pins).

2) That is correct.

Regards!

Jorge Gonzalez

[kaitav]

Hi Jorge,

Okay, I got it now. Thanks so much for your answers and time. Much appreciated.

Have a great weekend ahead!