STWBC2-HP datasheet(19/96 Pages) STMICROELECTRONICS

19 / 96 page

The detection circuit integrates two independent 20k pull-down resistor that can be enabled on DP and DM.

The detection circuit integrates a 100 µA current sink that can be applied either on DP or on DM.

Finally, the voltage on DP and DM are scaled down and filtered and then sent to the ADC mux (see

Section 2.1.4.7 ).

Figure 24. USB detection

The detection of USB source type is done by FW. It configures the USB detection circuit and uses ADC

measurements to check the response of source.

The first step of detection consists in checking the battery charging capability as per the USB BC 1.2

specification:

Primary detection: DP is driven at 0.6 V and DM is biased with 100 µA current sink. DM voltage is

measured.

Secondary detection: DM is driven at 0.6 V and DP is biased with 100 µA current sink. DP voltage is

measured.

Based on table below and DM/DP voltage measures, the FW can deduce the BC1.2 compatible type of

source.

Table 14. USB source type detection

Mode

USB source type

DP BIAS

DM BIAS

Check

Primary Detection

Dedicated charger

0.6 V

100 µA sink

DM > 0.4 V

USB host with charging cap

0.6 V

100 µA sink

DM > 0.4 V

Simple USB host

0.6 V

100 µA sink

DM ~ 0.0 V

Secondary Detection

Dedicated charger

100 µA sink

0.6 V

DP > 0.4 V

USB host with charging cap

100 µA sink

0.6 V

DP ~ 0.0 V

In case of dedicated charger detected, the FW proceeds in detection of high voltage charger. To do so:

Drive DP to 0.6 V and enable 100 µA sink on DM.

STWBC2-HP

Analog AFE functions

DS13825 - Rev 1.0

page 19/96

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