BQ24392 Implementation Guidelines
The system must define what is meant by low- 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 back down on how much current it is trying to draw until it finds a stable state with VBUS not
dropping.
3.4.2
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.
3.4.3
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 DBP timer as discussed in the
.
3.5
EVM Overview
The EVM for the BQ24392 is designed to be self-contained so no use of lab equipment is required to
evaluate the functionality of the battery charging detection or the USB communication capabilities.
However, there are test points available for more detailed analysis of the detection timings.
3.5.1
Board Power
The EVM is fully supplied by VBUS from the charger or PC connected to the board with test points for
monitoring VBUS as a device is attached. The EVM also has an LED output indicating when VBUS is
present as depicted in the following figure:
The EVM contains a 3.3-V output LDO for the SW_OPEN output and GOOD_BAT input as these pins
must not be connected to VBUS.
is the schematic for this portion of the design.
Figure 3. Schematic for 3.3-V Output LDO
6
BQ24392EVM User's Guide
SLVUA61 – April 2014
Copyright © 2014, Texas Instruments Incorporated