UCS1002-3 datasheet(39/114 Pages) MICROCHIP

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DS20006852A-page 39

UCS1002-3

8.0

DETECT STATE

8.1

Device Attach/Removal Detection

The UCS1002-3 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 UCS1002-3 contains circuitry to provide VBUS

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

VDD is the voltage source, whereas 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 is limited to IBUS_BYP, and

the Attach Detection feature is active.

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,

Attach Detection event occurs. This causes 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 is limited to that used to

detect device attachment (IDET_QUAL). Once an Attach

Detection event occurs, the UCS1002-3 waits for the

PWR_EN control to be enabled. When PWR_EN is

enabled and VS is above the threshold, the device

activates the USB port power switch and operates in

the selected Active mode (see Section 9.0 “Active

State”).

8.4

Removal Detection

The Removal Detection feature is 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 the Removal Detection event is flagged, the

following are performed:

Disable the port power switch and the bypass

switch.

Deassert the A_DET# pin and set the REM

status register bit.

Enable an internal discharging device that

discharges the VBUS line within tDISCHARGE.

Once the VBUS pin is discharged, the device

returns to the Detect state regardless of the

PWR_EN control state.

FIGURE 8-1:

Detect State VBUS Biasing.

Port Power

Switch

VDD

VBUS

Bypass

Switch

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