STCC5021 datasheet(16/37 Pages) STMICROELECTRONICS

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Application information

STCC5011, STCC5021

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DocID024660 Rev 6

5.5

Attach detection

The STCC5011-STCC5021 can detect peripheral device attachments when the host system

is in S4/S5 deep sleep states or in G3 shutdown state.

In these states, when no peripheral device is attached, the host system can save power by

switching off the high-power DC-DC converter and switching on a low-power LDO on the IN pin of

the device. When an attach event is detected, the device asserts the CHARGING/ATTACH

output allowing the host system to turn off the low power LDO and turn on the high power DC-

DC converter and start charging.

The attach detection feature is enabled with the combination of logic low level on EN and

logic high on ATTACH_EN (see Table 6). The devices already attached when activating the

attach detection circuit (EN = 0, ATTACH_EN = 1) are ignored and their current consumption is

limited to 500 μA. Only devices attached after activation of the attach detection circuit are

detected.

The attach detection block is supplied by the VDD power supply pin. It has a very low

consumption (12 µA typ.) and accepts a wide supply voltage range (1.7 V up to 5.5 V). The

VDD power supply must be provided by a dedicated low power LDO.

The attach detector monitors voltage drop across a bypass switch between VDD and the

OUT pin. The bypass switch is enabled only when the attach detector is turned on. This

voltage drop is caused either by the supply current of the attached device or by inrush

current for charging device internal capacitors.

The open drain active low output CHARGING/ATTACH is asserted upon device detection,

alerting the host system of device attachment. It stays asserted for the tATTACH delay

(25 s typically). During this time, the host system may switch the IN pin from low power LDO

to 5 V high-power supply and set proper CTLx configuration (see Figure 6).

The attached device can start charging keeping CHARGING/ATTACH asserted. If charging

does not occur, the flag is deasserted after the tATTACH (the attached device removed or

charging current drops below threshold or safety timer expires - see Section 5.6).

The supply voltage of the low-power LDO connected to the IN pin, when the system is in

power saving mode, must not be lower than the VDD power supply voltage level and must

not be greater than 5.5 V.

Table 6. Attach detector truth table

ATTACH_EN

Attach detector

OFF

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