USB3503 datasheet(48/73 Pages) MICROCHIP

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USB3503

DS00001584B-page 48

 2011-2015 Microchip Technology Inc.

8.0

BATTERY CHARGING

In order to detect the charger, the device applies and monitors voltages on the USBUP_DP and USBUP_DM pins. If a

voltage within the specified range is detected, the Charger Detection Register in the I2C register space shall be updated

to reflect the proper status.

8.1

Downstream Port Battery Charging Support

The USB3503 can configure any of the downstream ports to support battery charger handshake.

The Hub’s role in downstream battery charging is to provide an acknowledge to a device’s query as to if the hub system

supports USB battery charging. The hub silicon does not provide any current or power FETs or any such thing to actually

charge the device. Those components would need to be provided as external components in the final Hub board design.

If the final Hub board design provides an external supply capable of supplying current per the battery charging specifi-

cation, the hub can be configured to indicate the presence of such a supply to the device. This indication is on a per/port

basis. i.e. the board can configure two ports to support battery charging (thru high current power FET’s) and leave the

other port as a standard USB port.

8.1.1

USB BATTERY CHARGING

In the terminology of the USB battery charging specification, if the port is configured to support battery charging, the

downstream port is a “Charging Host Port”. All AC/DC characteristics will comply with only this type. If the port is not

configured to support battery charging, the port is a “Standard Host Port”. AC/DC characteristics comply with the USB

2.0 specification.

A downstream port will only behave as a “Charging Host Port” or a “Standard Host Port”. The port will not switch between

“Charging Host Port” or Standard Host Port” at any time after initial power-up and configuration.

8.1.2

SPECIAL BEHAVIOR OF PRTPWR REGISTER

The USB Battery charging specification does not address system issues. It only defines a low level protocol for a device

and host (or hub) to communicate a simple question and optional answer.

Device queries if the host to which it is connected supports battery charging.

The host will respond that it does support battery charging or does not respond at all. There is no negative response.

(A lack of response is taken as a negative response)

When ports are configured for downstream battery charging, the corresponding PRTPWR setting will be controlled by

downstream battery charging logic instead of the normal hub logic.

PRTPWR setting will assert after initial hub customer configuration (Internal default/Serial register writes). PRTPWR will

remain asserted and under the control of the battery charge logic until one of two events.

An overcurrent is detected on the corresponding OCS_N pin. In this case, PRTPWR setting will negate. The only

way to re-enable the PRTPWR setting from this state is to RESET the USB3503.

The hub enters Hub.Communication stage, connects on its upstream port and is enumerated by a USB host. In

this case, control over the PRTPWR setting reverts back to the hub logic inside the USB3503 and the normal

USB behavior applies. In this case, the host must enable PRTPWR.

FIGURE 8-1:

BATTERY CHARGING EXTERNAL POWER SUPPLY

SOC

VBUS

PRTPWR

USB3503

(Serial Mapped

INT

SCL

SDA

DC Power

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