STW4811MBRASLASHLF datasheet(51/85 Pages) STMICROELECTRONICS

51 / 85 page

STw4811M/STw4811N

Functional description

CD00131784

51/85

Data line pull-up resistance

The two bits of

USB control register dp_pullup and dn_pullup (Table 12) are used to

connect/disconnect pull-up resistors.

Full-speed and low-speed devices are differentiated by the position of the pull-up resistor

from the peripheral device. A pull-up resistor is connected to DP line for a full-speed device

and a pull-up resistor is connected to DN line for a low-speed device. The pull-up resistor

value is in the range of 900

Ω to 1600 Ω when the bus is idle and 1425 Ω to 3100 Ω when

the upstream device is transmitting.

Session Request Protocol (SRP)

To save power, the OTG supplement allows an A-device to leave the VBUS turned off when

the bus is not being used. If the B-device wants to use the bus when VBUS is turned off,

then it requires the A-device to supply power on VBUS using the Session Request Protocol

(SRP).

●

Initial conditions

The B-device does not attempt to start a new session until it has determined if the A-device

has detected the end of the previous session. The B-device must ensure that VBUS is

below VBUS_SESSION_END before requesting a new session.

Additionally, the B-device switches a pull-down resistor (R_VBUS_PD) from VBUS to

ground in order to quicken the discharge process as long as the B-device does not draw

more than 8 mA from VBUS. R_VBUS_PD is activated by bit ‘vbus_dischrg’ of

USB control

When the B-device detects that VBUS is below the VBUS_SESSION_END and that both

DP and DN have been low (SEO) for at least 2 ms, then any previous session on the A-

device is over and a new session can start.

●

Data-line pulsing

To indicate a request for a new session using the data line pulsing, the B-device turns on the

DP pull-up resistor for 5 ms to 10 ms (only at full speed, no DN pulsing). The DP pull-up

resistor is connected to VUSB (regulator output voltage). Timing is controlled by the USB

digital control.

●

VBUS pulsing

To indicate a request for a new session using the VBUS pulsing method, the B-device waits

for the initial conditions and then drives VBUS. VBUS is driven for a long enough period for

a capacitance on VBUS that is smaller than 2x6.5 µF to be charged to 2.1 V while a

capacitance on VBUS higher than 97 µF is not charged above 2.0 V. In this USB block, the

VBUS_SESSION_VALID threshold is used to determine if an A-device is DRD (dual role

device) or a standard host.

The B-device VBUS pulsing block is designed so that the maximum drawn current does not

exceed 8 mA. In this USB block, the pull-up is 600

Ω +/- 30%.

If a B-device is attached to a standard device, the pull-up must be disconnected after the

defined timing to prevent damage of standard hosts not designed to withstand a voltage

externally applied to VBUS.

STW4811MBRA/LF 数据表(PDF) 51 Page - STMicroelectronics

STW4811MBRA/LF 数据表(HTML) 51 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85

数据表下载