USB Embedded Master: requirement on power supply?

I'm going to design a board with an embedded USB Host connector (managed 
by Atmel SAM D21 MCU).

I will use that connection only for data communication with a smartphone 
or a pendrive. I don't need to recharge the battery of the smartphone. 
Of course, I need to supply the pendrive.

On my board I have to generate a +5V rail only for the USB, but I don't 
know what is its requirement. Could I use a 100mA regulator? Should I 
have a 500mA positive +5V rail?

pozz wrote:
> I'm going to design a board with an embedded USB Host connector (managed
> by Atmel SAM D21 MCU).
>
> I will use that connection only for data communication with a smartphone
> or a pendrive. I don't need to recharge the battery of the smartphone.

I'm not 100% sure you have a choice. Anybody know for sure?

> Of course, I need to supply the pendrive.
>
> On my board I have to generate a +5V rail only for the USB, but I don't
> know what is its requirement. Could I use a 100mA regulator? Should I
> have a 500mA positive +5V rail?


That rather depends on what will be plugged into it, doesn't it? You
should be able to configure the USB host/OTG hardware to negotiate only
for whatever current you choose.

-- 
Les Cargill

Il 27/07/2016 18:31, Les Cargill ha scritto:
> pozz wrote:
>> I'm going to design a board with an embedded USB Host connector (managed
>> by Atmel SAM D21 MCU).
>>
>> I will use that connection only for data communication with a smartphone
>> or a pendrive. I don't need to recharge the battery of the smartphone.
>
> I'm not 100% sure you have a choice. Anybody know for sure?

For sure the smartphone will detect a USB Host and will use it for 
battery recharge.  Howevere I don't know if this could work with 100mA 
only (I think 500mA must be negotiated between device and host... and my 
host could negate the 500mA requirement to the smartphone).


>> Of course, I need to supply the pendrive.
>>
>> On my board I have to generate a +5V rail only for the USB, but I don't
>> know what is its requirement. Could I use a 100mA regulator? Should I
>> have a 500mA positive +5V rail?
>
> That rather depends on what will be plugged into it, doesn't it?

Indeed I specified it: smartphone and pendrives.


> You
> should be able to configure the USB host/OTG hardware to negotiate only
> for whatever current you choose.

So I could live with 100mA only... if my host doesn't let the connected 
device to require more current... but I'm not sure.

pozz wrote:
> Il 27/07/2016 18:31, Les Cargill ha scritto:
>> pozz wrote:
>>> I'm going to design a board with an embedded USB Host connector (managed
>>> by Atmel SAM D21 MCU).
>>>
>>> I will use that connection only for data communication with a smartphone
>>> or a pendrive. I don't need to recharge the battery of the smartphone.
>>
>> I'm not 100% sure you have a choice. Anybody know for sure?
>
> For sure the smartphone will detect a USB Host and will use it for
> battery recharge.  Howevere I don't know if this could work with 100mA
> only (I think 500mA must be negotiated between device and host... and my
> host could negate the 500mA requirement to the smartphone).
>
>

Right. That's the theory.

>>> Of course, I need to supply the pendrive.
>>>
>>> On my board I have to generate a +5V rail only for the USB, but I don't
>>> know what is its requirement. Could I use a 100mA regulator? Should I
>>> have a 500mA positive +5V rail?
>>
>> That rather depends on what will be plugged into it, doesn't it?
>
> Indeed I specified it: smartphone and pendrives.
>

That just narrows the field. Pendrives can ask for quite a bit; they're
getting to be 64 GB and up. Had I not run into pendrives asking for
more than 100 mA , I would not have commented :)

>
>> You
>> should be able to configure the USB host/OTG hardware to negotiate only
>> for whatever current you choose.
>
> So I could live with 100mA only... if my host doesn't let the connected
> device to require more current... but I'm not sure.
>

Nor am I.

-- 
Les Cargill