BQ24392_15 Datasheet, PDF (9/22 Pages) Texas Instruments – bq24392 Dual SPST USB 2.0 High Speed Switch with USB Battery Charging Specification Revision 1.2 Detection

www.ti.com
8 Application and Implementation
bq24392
SLIS146C – JUNE 2012 – REVISED JANUARY 2015
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
8.1.1 Using the BQ24932 GPIOs
8.1.1.1 CHG_AL and CHG_DET
The BQ24392 has 2 charger indicators, CHG_AL_N and CHG_DET, that the host can use 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
High-Z
Low
Low
CHG_DET
X
Low
High
Charging is not allowed
Low-current charging is allowed
High-current charging is allowed
The system must define what is meant by low-current and high-current charging. If CHG_DET is high, a system
could try to draw 2 A, 1.5 A, or 1.0 A. If the system is trying to support > 1.5-A chargers, then the system has to
use a charger IC that is capable of monitoring the VBUS voltage as it tries to pull the higher current values. If the
voltage on VBUS starts to drop because that high of a current is supported then the system has to reduce the
amount of current it is trying to draw until it finds a stable state with VBUS not dropping.
8.1.1.2 SW_OPEN
SW_OPEN is an open drain output that indicates whether the USB switches are opened or closed. In the High-Z
state the switches are open and in the active, or low state, the switches are closed. The host should monitor this
pin to know when the switches are closed or open.
8.1.1.3 GOOD_BAT
GOOD_BAT is used by the host controller to indicate the status of the battery to the BQ24392. This pin affects
the switch status for a SDP or CDP, and it also affects the Dead Battery Provision (DBP) timer as discussed in
the Charger Detection section.
8.1.1.4 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+ and D– lines to run detection. This is why the BQ24392 has a standard 130-ms debounce time after VBUS
valid to run the detection algorithm. This delay helps minimize the effects of the D+ and D– lines making contact
after VBUS and GND.
Figure 4 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).
Copyright © 2012–2015, Texas Instruments Incorporated
Submit Documentation Feedback
9