FUSB307BVMPX datasheet(16/57 Pages) ONSEMI

16 / 57 page

FUSB307B

www.onsemi.com

Automatic Sink Discharge after a Disconnect

Automatic discharge can be enabled by setting

PWRCTRL. AUTO_DISCH register bit. When in Sink

mode the FUSB307B will fully discharge VBUS to vSafe5V

(max.) within tSafe5V and to vSafe0V within tSafe0V when

a disconnect occurs. The FUSB307B is in Sink mode any

time MSGHEADR.POWER_ROLE = 0.

Whenever the system is sinking voltages greater than

vSafe5V, a disconnect will be detected based on

VBUS_SNK_DISC registers.

If the system is only sinking vSafe5V, a disconnect will be

detected when VBUS_VAL goes low.

Due to the high capacitance on VBUS (up to 100 F) the

FUSB307B may not immediately know if VBUS has been

removed. The FUSB307B with Automatic Discharge on

will apply RBLEED discharge load to VBUS until it crosses

below VBUS_SNK_DISC.

The FUSB307B has to detect a disconnect within

tDisconnectDetect

ms)

from

VBUS

crossing

VBUS_SNK_DISCL. Once the FUSB307B has detected a

Disconnect, RFULL_DISCH will be enabled bringing the

VBUS voltage down to vSafe0V.

Whenever the FUSB307B detects a Disconnect, it will not

present Rd (or Rp) until VBUS reaches vSafe0V.

When the VBUS voltage goes below vSafe0V, the

auto−discharge circuit will disable.

If the discharge of VBUS to below vSafe0V is not

accomplished by tSafe0V (650 ms), the FUSB307B will set

the interrupt

NOTE:

ALERTL.I_PORT_PWR is asserted if the

bit−wise AND of PWRSTAT and

PWRSTAMSK results in any bits that have the

value 1.

ALERTH.

I_FAULT

bit

and

the

status

FAULTSTAT.DISCH_FAIL. The discharge circuit is not

turned off when this happens.

In tSinkDischargeBleed + tSinkDischargeFull have to be

less than tSafe5V to comply with USB−PD spec.

Figure 15. VBUS Auto Discharge as SinkSource

Cable Disconnect

tSafe5V

tSafe0V

vSafe0V

vSafe5V

time

VBUS

VBUS_SNK_DISC

tSinkDischargeBleed

tSinkDischarge Full

tDisconnectDetect

Apply RFULL_DISCH

RBLEED

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