STW4810 datasheet(46/78 Pages) STMICROELECTRONICS

46 / 78 page

Functional description

STw4810

46/78

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Host Negotiation Protocol (HNP)

At the start of a session, the A-device has the role of host as default. During a session, the

host role can be transferred back and forth between the A-device and the B-device any

number of times using the Host Negotiation Protocol (HNP). The process for this exchange

of host role is described in the “On the Go Supplement to the USB 2.0 Specification” (rev

1.0).

ID detector

In either active or suspended power mode, the ID detector detects the condition of the ID

line and differentiates between the following three conditions:

–

ID ball floating: (e.g. with USB B-device connected)

–

ID ball shorted to ground: (e.g. with USB A-device connected)

–

ID ball connected to ground through resistor RACC_ID: (e.g.with an accessory).

The transceiver pulls the ID ball to VID_HI (VBAT) through a resistance of RID_PU when an

accessory is plugged in. In this case, the ID ball is externally connected to ground via

Racc_ID resistor.

Two comparators are used to detect the ID voltage: VID_GND and VID_FLOAT.

The ID detector also has a switch that can be used to ground the ID ball. This switch is

controlled by id_gnd bit of USB control register 2 (

Table 12); This pull-down is used for

CEA_KARKIT purposes.

Car kit interrupt detector

The transceiver is able to detect when the DP line is below the Carkit Interrupt threshold

‘cr_int’, (see USB interrupt register) (refer to OTG specifications, Rev 0.92, §2.7, p13).

Charge pump

From VBAT_USB, the charge pump supplies VBUS, ‘vbus_drv’ bit of USB control register 2

(

Table 12) is used to enable/disable the charge pump.

LDO USB

From VBAT_USB, a LDO provides VUSB supply, ‘usb_en’ bit of USB_EN register (

Table 17)

is used to enable/disable the VUSB LDO.

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