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Data Lines
VBUS and
Ground
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BQ24392 Implementation Guidelines
3.2 Slow Plug-in Event
As you insert a charger into the USB receptacle, the pins are configured so that the VBUS and GND pins
make contact first. This presents a problem as the BQ24392 (or any other charger detection IC) requires
access to the D+ D– lines to run detection. This is why the BQ24392 has a standard 130 ms de-bounce
time after VBUS valid to run the detection algorithm. This delay helps minimize the effects of the D+ D–
lines making contact after VBUS and GND.
Figure 2 is from the datasheet of a standard male micro-USB connector and shows how the data
connections (red line) are slightly recessed from the power connections (blue line).
Figure 2. Data Connections Recessed from Power Connections
However, in some cases the charger is inserted very slowly, causing the VBUS and GND to make contact
long before D+ D–. Due to this effect, there is no guaranteed detection time as the detection time can vary
based on how long it takes to insert the charger. If longer than 600 ms is taken to insert the charger into
the USB receptacle, the detection algorithm of the BQ24392 will timeout and instead of the charger being
detected as a DCP, it is now detected as a nonstandard charger (D+ and D– floating).
3.3 DBP Timer
The BQ24392 features a dead battery provision timer per the BC1.2 specification. Once a charger has
been detected and the GOOD_BAT pin is low, a dead battery timer is initiated. If the GOOD_BAT
continues to be LOW for 30 minutes (maximum of 45 minutes), charging is disabled and CHG_AL_N goes
into the High-Z state to indicate this. Toggling GOOD_BAT high after the DBP timer expires re-starts
detection and the DBP timer.
3.4 Using the BQ24932 GPIOS
3.4.1 CHG_AL and CHG_DET
The BQ24392 has 2 outputs, CHG_AL_N and CHG_DET, that the host can used to determine whether it
can charge and if it can charge at a low or high current.
Table 2 demonstrates how these outputs should
be interpreted. CHG_AL_N is an open drain output and is active when the output of the pin is low.
CHG_DET is a push-pull output and is high in the active state.
Table 2. BQ24392 Outputs
CHG_AL_N CHG_DET
High-Z X Charging is not allowed
Low Low Low-current charging is allowed
Low High High-current charging is allowed
5 SLVUA61 – April 2014 BQ24392EVM User's Guide
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