MX283 PMU USB without 5V power supply

[rajtantajtan]

Hello,

I have a little problem understanding the MX283 PMU. Our design does not include a 5V power supply at the moment, only a 4.2V and a 3.8V power supply, these two could be seen as li-ion batteries and one of them connected to DCDC_BATT on MX283.

However I read on freescale community that to use USB you must supply  5V on VDD5V-pin. Re: USB with 3.3V (no VDD5V)

MX28 Technical Data pdf says this:

PMU:

• Generates USB-Host 5-V from Li-Ion battery (using PWM).

However I cant find anything in MX28 PMU about this amazing feature.

So is it possible to use USB without having to supply 5V to VDD5V or do I have to use some kind of voltage booster to get 5V and connect it to VDD5V?

[rajtantajtan]

And another very related question. If we supply VDD5V with 5V, is it possible to configure CPU so it only uses power from DCDC_BATT and BATTERY?

If this is possible we could  implement a small cheap  low current DCDC booster to provide 5V but still use our power supply (3.8V) to provide power to CPU and all other components.

[AnsonHuang]

Hi, Rajtantajtan

     Sorry that I can NOT answer your first question, as I am only a SW guy and we didn't implement this boost feature before, I think maybe a hardware design guy can help.

     For your second question, the answer is yes. When there is 5V connected, you will receive a interrupt, then you can decide whether to switch the power source from battery to DCDC4P2, you can refer to our BSP. We have implemented the feature of USB current limit, when a device connect to PC USB port, we can only get < 100mA from VBUS before USB device is enumerated. The basic method is that, if you want to use battery power, don't enable DCDC4P2.

[Yuri]

> If we supply VDD5V with 5V, is it possible to configure CPU so it only uses power from DCDC_BATT and BATTERY?ssible.

This is possible. Please use section 4.1.1.2 (DCDC_BATT source only: software configuration) of app note

AN4199, Rev. 1, 03/2013 ("Using the i.MX28 Power Management Unit and Battery Charger

Getting Started with Power Supply").

[rajtantajtan]

And I will have reliable USB ports even if not using power from VDD5V?

[arthur_lai]

The i.MX28 does not have a boost converter to provide a 5V output from lower voltage like 3.8 or 4.2V. You will need an external booster as you mentioned.

For USB operations, you do not need to supply VDD5V. The USB block is using the internal supplies generated from DCDC_BATT, not VDD5V.

Thanks,

Arthur

[Yuri]

It depends on ...

If the i.MX28 USB OTG will be used in host USB mode, and some VBUS current will be requested by a USB device, connected
to the host - we will get problems.

[rajtantajtan]

I'm planning to use my USB ports as host all the time and I will provide USB devices with 5V from my booster, what kind of problems can I expect if I disable VDD5V?