STCC5021 datasheet(19/37 Pages) STMICROELECTRONICS

19 / 37 page

DocID024660 Rev 6

19/37

STCC5011, STCC5021

Application information

Use case 1: device charging in CDP, notebook is then turned off

If a device is charging while the system is turned off and the battery supplied, the risk is that

the charging process stops before the end of charge due to the system power-off. To avoid

this, the flag CHARGING/ATTACH can be used by the host to prevent the switching-off of

the high power DC-DC converter when the host goes to S5 state, even if battery supplied. In

this case the 3-h timer is not started.

Use case 2: charging in S5, battery supplied

Once device attachment has been detected and the host has woken up, supplying VBUS

voltage to the portable device allows the charging process to start in DCP mode. The flag

CHARGING/ATTACH stays asserted for the tATTACH period (25 s typ.) after attach. During

this period, the charging must be established (charging current above the IOUT_TH

threshold) to keep the CHARGING/ATTACH output asserted. The 3-h safety timer is started

if ATTACH_EN is kept high.

If, for whatever reason, there is no charging current (or if it is below 20 mA),

CHARGING/ATTACH is deasserted (while ATTACH_EN is still high). The host can return to

its previous state by switching off the high power supply and switching on the low-power LDO, to

reduce consumption, and setting the EN pin to 0. Therefore, the attach detector is ON. At

this stage, the STCC5011-STCC5021 devices can detect if the device is still attached or has

been removed (see Figure 9).

•

If the device is still attached, the attach detector circuit waits for device removal.

•

If the device is removed, the circuit goes back into attach detection mode till the next

attachment.

Figure 9. Attach detection

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