STCC2540 datasheet(13/32 Pages) STMICROELECTRONICS

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STCC2540

Application information

5.2

Remote wakeup in S3

For more information refer to Section 5.4: State machine.

If the CTLx pins are controlled by hardware signals (such as SLP_Sx# or SUSPEND), the

CTLx combination changes when host transitions from S0 to S3 and back. In this case, the

STCC2540 device can support remote wakeup of portable devices for the following

transitions (i.e. no VBUS discharge pulse and data switch ON):

•

SDP S0 (CTLx = 110) to and from SDP S3 (CTLx = 010) for all USB devices

•

SDP (CTLx = x10) and CDP S0 (CTLx = 111) to and from CDP S3 (CLx = 011) for low-

speed USB devices only.

If the host system is in S3 mode (CTLx = 011), the system automatically turns into DCP auto

mode for already attached full-speed / high-speed USB devices or after any USB device is

detached. Thus, already attached full-speed / high-speed devices or newly attached devices

are charged without the need of CTLx transition.

If the S0 to S3 transition is managed by GPIO from the embedded controller, the easiest

solution is to keep the same levels on the CTLx pins (SDP or CDP modes). Therefore,

remote wakeup in S3 is supported for all USB devices but the system does not

automatically turn into DCP auto mode.

5.3

VBUS discharge

The VBUS discharge pulse lasts for 350 ms typ. (tVBUS_REAPP) and is performed for any

transitions between the modes listed in Table 5, except the modes allowing remote wakeup

in S3 [transitions (x10) and (111) to/from (011)] (see Section 5.4).

Permanent output discharge is provided in following modes:

•

EN = 0, CTLx = xxx (ignored)

•

EN = 1, CTLx = 000.

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