STW4811MBRATSLASHHF datasheet(52/85 Pages) STMICROELECTRONICS

52 / 85 page

Functional description

STw4811M/STw4811N

52/85

CD00131784

●

Session Request Protocol (SRP)

If the B-device is in correct condition to start a new session, it first performs data line

pulsing, followed by VBUS pulsing. When VBUS next crosses the SESSION VALID

threshold, the B- device considers a session to be in progress and asserts the DP or DN

data line within 100 ms. After SRP initialization, the B- device is set up to wait for at least 5

seconds for the A-device to respond before informing the user that the consumption attempt

has failed.

●

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 sequence of events for this

exchange of host role is described in the “On the Go Supplement to the USB 2.0

Specification” (rev 1.0) as follow:

–

The A-device puts the bus in the suspend state

–

The B-device simulates a disconnect by de-asserting its DP pull-up

–

The A-device detects SE0 on the bus and asserts its DP pull-up

–

The B-device detects that DP line is high and takes the role of the host.

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 (

Figure 13).

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 car kit interrupt threshold

‘cr_int’, (see

USB interrupt register in Table 13 and 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.

If VBUS is “ON” before going to sleep mode, it remains “ON” in sleep mode.

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 and the transceiver.

STW4811MBRAT/HF 数据表(PDF) 52 Page - STMicroelectronics

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