TUSB3410 - getting bMaxPower

thierry Didi

Other Parts Discussed in Thread: TUSB3410

Hello,

We are designing an application using an MSP430F5438 and a TUSB3410. Our application ca be charged over usb, for instance when it is connected to a PC.

We would like to draw as much current as authorized from the usb port for charging our battery. We could set bMaxPower in the configuration descriptor to 500mA, for instance. But what if the PC does not allow to draw more than 100mA ? I think that some negociation will take place between the TUSB3410 and the PC to fallback to 100mA.

So my question is: is there a way to retrieve, from the MSP430 (connected through I2C to the MSP430F5438) what is the maximum current that can be drawn from the usb port to which the TUSB3410 is currently connected ?

Thanks,

Thierry

over 14 years ago

0 JMMN over 14 years ago

TI__Guru 60870 points

Hello Theirry,

The TUSB3410 does not have the ability to connect as a 100 mA device and then disconnect and reconnect as a 500 mA based on the power budget of the USB host. In general, the TUSB3410 does not have the ability to support two configurations and swap between the two. Using a power management device that supports the USB battery charging may be the best solution.

Julie

0 thierry Didi over 14 years ago in reply to JMMN

Intellectual 410 points

Hello Julie,

Thanks for your answer, but I am not sure to understand your point: we are using an STW4102 component for the battery charging. This component can be configured by SW to draw either 100mA or 500mA or 1A from the USB port. The point is that we don't know which value to configure, as it depends on the capability of the other end of the link.

Then, I wanted to know if the TUSB3410 was able to notify the host processor of the of capabilities of the other end of the USB port ? For instance, what would happen if the TUSB3410 is configured as a 500mA device but the usb port of the PC cannot provide more than 100mA ? Will there be some error notified ?

(sorry if I missed something in your answer)

Thanks,

Thierry

0 JMMN over 14 years ago in reply to thierry Didi

TI__Guru 60870 points

Hello Thierry,

A USB host does not notify downstream devices of its power budget, so the TUSB3410 cannot configure the battery charging component. If the TUSB3410 is set up with bMaxPower set to 500 mA and the USB host can only provide 100 mA, the host will not configure the TUSB3410 after reading in the initial descriptors. Any unconfigured USB device is limited to power consumption of 100 mA, this state does not generate errors since it is the expected behavior per the USB 2.0 spec.

Regards,

Julie Nirchi

0 thierry Didi over 14 years ago in reply to JMMN

Intellectual 410 points

Hi Julie,

Thanks for your answer. It's clear to me now,

Best regards,

Thierry

0 DHarmon over 14 years ago in reply to thierry Didi

TI__Genius 16430 points

Just one additional comment - a USB 2.00 host MUST provide 500mA of power. An embedded host or OTG device may supply less, but a standard PC host must supply the full 500mA. However, if you are connected downstream from a bus-powered hub, they are only required to provie 100mA - these are not very common, and as Julie points out, if you plug a 500mA device into a bus-powered hub, the host will not configure it.

0 thierry Didi over 14 years ago in reply to DHarmon

Intellectual 410 points

Thanks,

I think that I know how I will proceed for drawing as much current as possible from the PC (in order to charge the battery of my embedded system as fast as possible):

- I will configure TUSB3410 at 500mA by default, but I will only authorize the STW4102 to draw 100mA

- When I will connect my board to a PC,

If the PC is OK, the USB port will be configured and my application running on the PC will send a message to my application running in the board through the COM port to allow the STW4102 to draw 500mA.
If the PC is not OK, the USB port won't come up: after a given timeout, I would reset the TUSB3410, provide it with a new device descriptor asking only 100mA, and work at this current.

What do you think ?

Best Regards,

Thierry

0 JMMN over 14 years ago in reply to thierry Didi

TI__Guru 60870 points

Thierry,

Your implementation is sound except there is no way to provide the TUSB3410 with a new device descriptor and have it re-enumerate as a 100 mA device. The TUSB3410 loads in the device descriptors from EEPROM or from a driver residing on the USB host and it is not possible to change descriptors after the initial download.

Regards,

Julie Nirchi

0 thierry Didi over 14 years ago in reply to JMMN

Intellectual 410 points

Thanks Julie,

In our case, we "emulate" the E2PROM with an MSP430 connected on the I2C (this is an implementation proposed in a TI application Note). So I think that we can manage to reset to TUSB3410 and provide it with a new E2PROM image through the MSP430

Thanks for all your detailed answers and for your support. It was very helpful,

Best Regards

Thierry

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TUSB3410 - getting bMaxPower