BQ24157 Datasheet, PDF (16/39 Pages) Texas Instruments – Fully Integrated Switch-Mode Charger With USB Compliance and USB-OTG Support

bq24157
SLUSB80 – SEPTEMBER 2012
www.ti.com
DETAILED FUNCTIONAL DESCRIPTION
For a current restricted power source, such as a USB host or hub, a high efficiency converter is critical to fully
use the input power capacity for quickly charging the battery. Due to the high efficiency for a wide range of input
voltages and battery voltages, the switch mode charger is a good choice for high speed charging with less power
loss and better thermal management than a linear charger.
The bq24157 are highly integrated synchronous switch-mode chargers, featuring integrated FETs and small
external components, targeted at extremely space-limited portable applications powered by 1-cell Li-Ion or Li-
polymer battery pack. Furthermore, bq24157 also has bi-directional operation to achieve boost function for USB
OTG support.
The bq24157 have three operation modes: charge mode, boost mode, and high impedance mode. In charge
mode, the IC supports a precision Li-ion or Li-polymer charging system for single-cell applications. In boost
mode, the IC boosts the battery voltage to VBUS for powering attached OTG devices. In high impedance mode,
the IC stops charging or boosting and operates in a mode with very low current from VBUS or battery, to
effectively reduce the power consumption when the portable device is in standby mode. Through I²C
communication with a host, referred to as "HOST" control/mode, the IC achieves smooth transition among the
different operation modes. Even when no I²C communication is available, the IC starts in default mode. During
default mode operation, the charger will still charge the battery but using each register's default values.
Input Voltage Protection
Input Overvoltage Protection
The IC provides a built-in input overvoltage protection to protect the device and other components against
damage if the input voltage (Voltage from VBUS to PGND) goes too high. When an input overvoltage condition is
detected, the IC turns off the PWM converter, sets fault status bits, and sends out a fault pulse from the STAT
pin. Once V_BUS drops below the input overvoltage exit threshold, the fault is cleared and charge process
resumes.
Bad Adaptor Detection/Rejection
Although not shown in Figure 24, at power-on-reset (POR) of VBUS, the IC performs the bad adaptor detection
by applying a current sink to VBUS. If the VBUS is higher than V_IN(MIN) for 30ms, the adaptor is good and the
charge process begins. Otherwise, if the VBUS drops below V_IN(MIN), a bad adaptor is detected. Then, the IC
disables the current sink, sends a send fault pulse in FAULT pin and sets the bad adaptor flag (B2 - B0 = 011 for
Register 00H). After a delay of T_INT, the IC repeats the adaptor detection process, as shown in Figure 25 and
Figure 26.
Adpator
VBUS
VBUS
I_SHORT
(30 mA)
Adaptor Detection Control
GND
PGND
V_IN
V_IN(MIN)
V_{IN_GOOD}
Deglitch
30ms
V_{IN_POOR}
START
Delay
T_INT
Figure 25. Bad Adaptor Detection Circuit
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