FUSB251 datasheet(9/19 Pages) ONSEMI

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FUSB251

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FUNCTIONAL SPECIFICATIONS

POR and Reset

The FUSB251 closes both CC and SBU switches with a

valid VDD supply after Power On reset. Until valid VDD is

supplied, FUSB251 presents Rd on both CC1 and CC2 so

that a source device can provide Vbus and Type−C controller

can present Rd continuously after POR so VBUS will be

consistent. At UVLO condition which is 2.4 volt (falling),

CC and SBU switches get open again and Rd will be

presented on both CC.

There is device reset register, bit0 in 0x0B register. If the

so momentarily both switches will be open and closed back.

CC and SBU Switch Characteristics

The FUSB251 has 2x SPST switches on both CCx and

SBUx with OVP feature. Both CC and SBU switch paths are

closed automatically with valid Vdd supply. CC switch is

used for Type−C / PD communication channel. Also Vconn

can be provided through the switch from CCx_H to CCx. Up

to 1A Vconn current can be provided over the low Ron(0.3

W) path. Both CCx and SBUx pins are 24 volt DC−tolerant.

SBU switch can be used for DisplayPort Aux channels

following USB PD Alternative mode or UART.

Dead Battery Mode

Upon dead battery condition, the both CC1/2 ports present

Rd(5.1 k

W) pull down to allow a Type−C source device to

attach and provide Vbus to the sink which is under dead

battery mode. Once system power comes back and valid

VDD supplied to FUSB251, the dead battery Rd is removed

and both CC switches are closed. Then, Type−C / PD

controller can detect the attached Type−C source device.

Over Voltage Protection

When an over−voltage event is detected on either CCx or

SBUx, the FUSB251 will activate OVP circuit to open the

switch within tOVP. The OVP event is independent between

CC and SBU. Any CC channel OVP opens the CC1 and CC2

switch path only, and SBU switch is keep closed. OVP on

SBU opens the SBU switch only. Upon the detection of an

over−voltage event, the INTB pin is asserted low to notify

processor with register update.

When OVP condition is removed from the port, the switch

path is closed automatically and OVP recovery interrupt is

generated to notify processor. Getting interrupt service is not

required to close the switch back. OVP function is only

working on the connector face ports, CCx and SBUx.

FM Pin

FM pin is for Factory test Mode (FM) purpose. When

Factory test mode is used over Type−C connector and if host

device needs to detect Factory Test fixtures by using ID with

ADC function, the FM can be used by connecting FM to

ADC input port in the processor. Without any external pull

down on FM PIN, FM can be switched to one of SBU pins,

default is SBU1 and it can be manually switched over to

SBU2 if needed. The other SBU2 or SBU1 pin will be open.

If Factory test mode is not needed, pull down(less than

10 k

W) or direct connecting to GND makes switch close

between SBUx_H and SBUx after POR or reset.

Manual Mode Control

For switch, there is manual mode switch control for CC

and SBU switches. Processor can manually open or close the

switch paths in the FUSB251 even though both switches are

closed in default with valid VDD. Manual mode switch

configuration overrides the auto switch control. However,

there are exceptions, such as during moisture detection

process and OVP event because switch has to be open in

these cases. The switch configuration has to be set in the

switch control register and then, bit 0 of control register has

to be set.

Surge and ESD Protection

The FUSB251 connector facing ports, CCx and SBUx, are

designed to endure up to

±35volt surge protection. The

voltage can occur when 20 volt DC voltage from VBUS

touches the CC and SBU pins with the inductance inside

cable. Also, system ESD protection, IEC61000−4−2, is

supported with the external capacitor on CAP pin.

Capacitor Recommendation

The CAP pin needs an external capacitor ranges 0.1

mF to

1.0

mF. Recommended capacitor type is X7R which has low

capacitance variation with temperature change and 0603 or

larger size. Also the capacitor rated voltage is important

because the voltage on the CAP could be greater than 35 volt

with Surge or hot plug in the Type−C cable so 50 volt or

larger rated capacitor is recommended.

Interrupt Service

FUSB251 has INTB pin to notify processor the status

change in the device. Any change in the Interrupt register

will trigger the INTB pin which is open drain output.

INTB is ready after POR or reset without any register set.

Once INTB pin is triggered to low, the pin stays low until the

interrupt register is read by processor. The interrupt mask

registers are default disabled. If any interrupt mask bit is set,

the corresponding interrupt register bit won’t set, so INTB

pin won’t be triggered.

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