FUSB307BVMPX datasheet(15/57 Pages) ONSEMI

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FUSB307B

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VBUS Monitoring and Measurement

The FUSB307B can monitor the presence of VBUS and

will report it on PWRSTAT.VBUS_VAL and interrupt

ALERT.I_PORT_PWR.

VBUS_VAL is set according to VBUS thresholds in

vVBUSthr.

The FUSB307B also supports a more precise voltage

measurement via an on−board ADC. The voltage on VBUS

is measured at a rate of tVBUSsample and it is reported on

VBUS_VOLTAGE_L/H register. The precision of the

measurement is +/2% with a resolution of 25 mV LSB.

In addition to providing the

μProcessor an accurate

measurement

VBUS,

the

measurement

VBUS_VOLTAGE will be used when monitoring various

user defined thresholds:

• Voltage alarms in registers VALARMLCFG and

VALARMHCFGL

• VBUS

Disconnect

Threshold

registers

VBUS_SNK_DISCL and VBUS_SNK_DISCH

• VBUS Stop Discharge Threshold in registers

VBUS_STOP_DISCL and VBUS_STOP_DISCH

• The FUSB307B implements Low and High VBUS

Voltage

Alarms

that

can

programmable

via

VALARMLCFG and VALARMHCFG respectively. If

the High or the Low thresholds are crossed, the

FUSB307B

will

signal

interrupt

ALERTL.I_VBUS_ALRM_HI or

ALERTH.I_VBUS_ALRM_LO respectively.

These

alarms

can

disabled

writing

PWRCTRL.DIS_VALARM to one

ALERTL.I_PORT_PWR is asserted if the bit−wise AND

of PWRSTAT and PWRSTAMSK results in any bits that

have the value 1.

VBUS Discharge

Manual Discharge

There are two types of manual discharge circuits

implemented: A bleed discharge for low current and a force

discharge. The bleed discharge can be manually enabled by

writing

one

bit

PWRCTRL.EN_BLEED_DISCH. When enabled, the bleed

discharge provides a low current load on VBUS of 7 k

(max.) via RBLEED. The force discharge is used to quickly

discharge VBUS to vSafe0V by applying a dynamic load to

VBUS via RFULL_DISCH. The force discharge can be

manually enabled by writing a one to register bit

PWRCTRL.FORCE_DISCH. When RFULL_DISCH is

applied, the maximum slew rate allowed for discharging

VBUS does not exceed vSrcSlewNeg 30 mV/

μs as it is

specified in the USB−PD spec.

Automatic discharge bit PWRCTRL. AUTO_DISCH

must be disabled before enabling force discharge.

Automatic Source Discharge after a Disconnect

Automatic discharge can be enabled by setting

PWRCTRL. AUTO_DISCH register bit. When in Source

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 Source mode

when the SRC output is asserted.

The FUSB307B in Source mode will detect a Disconnect

if the CCSTAT.CCx_STAT field for the monitored CC pin

indicates SRC.Open and enable the FULL Discharge

pull−down device. The monitored CC pin is specified by

TCPC_CTRL.ORIENT.

Figure 14. VBUS Auto Discharge as Source

Cable Disconnect

(CCSTAT change)

tSafe5V

tSafe0V

vSafe0V

vSafe5V

time

VBUS

Apply R

FUSB307BVMPX Datasheet(PDF) 15 Page - ON Semiconductor

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