UCS81003 datasheet(39/108 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS20005334A-page 39

UCS81003

8.0

DETECT STATE

8.1

Device Attach/Removal Detection

The UCS81003 can detect the attachment and removal

of a portable device on the USB port. Attach and

Removal Detection does not perform any charger

emulation or qualification of the device. The high-speed

switch is “off” (by default) during the Detect power state.

8.2

VBUS Bypass Switch

The UCS81003 contains circuitry to provide VBUS

current as shown in Figure 8-1. In the Detect state, VDD

is the voltage source; in the Active state, VS is the

voltage source. The bypass switch and the port power

switch are never both on at the same time.

While the VBUS bypass switch is active, the current

available to a portable device will be limited to

IBUS_BYP, and the Attach Detection feature is active.

FIGURE 8-1:

Detect State VBUS Biasing.

8.3

Attach Detection

The primary Attach Detection feature is only active in

the Detect power state. When active, this feature

constantly monitors the current load on the VBUS pin. If

the current drawn by a portable device is greater than

IDET_QUAL for longer than tDET_QUAL, an Attach

Detection event occurs. This will cause the A_DET# pin

to assert low and the ADET_PIN and ATT status bits to

be set.

Until the port power switch is enabled, the current

available to a portable device will be limited to that used

to detect device attachment (IDET_QUAL). Once an

Attach Detection event occurs, the UCS81003 will wait

for the PWR_EN control to be enabled (if not already).

When PWR_EN is enabled and VS is above the

threshold, the UCS81003 will activate the USB port

power switch and operate in the selected Active mode

(see Section 9.0 “Active State”).

8.4

Removal Detection

The Removal Detection feature will be active in the

Active and Detect power states if S0 = ‘1’. This feature

monitors the current load on the VBUS pin. If this load

drops to less than IREM_QUAL_DET for longer than

tREM_QUAL, a Removal Detection event is flagged.

When this event occurs, the following will be performed:

Disable the port power switch and the bypass

switch.

De-assert the A_DET# pin and set the REM

status register bit.

Enable an internal discharging device that will

discharge the VBUS line within tDISCHARGE.

Once the VBUS pin has been discharged, the

device will return to the Detect state regardless

of the PWR_EN control state.

Port Power

Switch

VDD

VBUS

Bypass

Switch

VBUS

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