BQ24157 Datasheet, PDF (18/39 Pages) Texas Instruments – Fully Integrated Switch-Mode Charger With USB Compliance and USB-OTG Support

bq24157
SLUSB80 – SEPTEMBER 2012
www.ti.com
Battery Short Protection
During the normal charging process, if the battery voltage is lower than the short-circuit threshold, V_SHORT, the
charger operates in short circuit mode with a lower charge rate of I_SHORT.
Battery Detection in Host Mode
For applications with removable battery packs, the IC provides a battery absent detection scheme to reliably
detect insertion or removal of battery packs.
During the normal charging process with host control, once the voltage at the CSOUT pin is above the battery
recharge threshold, V_OREG- V_RCH, and the termination charge current is detected, the IC turns off the PWM
charge and enables a discharge current, I_DETECT, for a period of t_DETECT, (262 ms typical) then checks the battery
voltage. If the battery voltage is still above the recharge threshold after t_DETECT, the battery is present. On the
other hand, if the battery voltage is below the battery recharge threshold, the battery is absent. Under this
condition, the charge parameters (such as input current limit) are reset to the default values and charge resumes
after a delay of T_INT. This function ensures that the charge parameters are reset whenever the battery is
replaced.
15-MINUTE SAFETY TIMER
The bq24157 stays in 15-minute (default) mode indefinitely until I²C communication begins. When I²C
communication begins, the host processor does not need to reset this 15 minutes timer while charging the
battery.
USB FRIENDLY POWER UP
The default control bits set the charging current and regulation voltage low as a safety feature to avoid violating
USB spec and over-charging any of the Li-Ion chemistries, while the host has lost communication. The input
current limiting is described below.
INPUT CURRENT LIMITING AT POWER UP
The input current sensing circuit and control loop are integrated into the IC. When operating in default mode, the
OTG pin logic level sets the input current limit to 100mA for a logic low and 500mA for a logic high. In host mode,
the input current limit is set by the programmed control bits in register 01H.
CHARGE MODE OPERATION
Charge Profile
Once a good battery with voltage below the recharge threshold has been inserted and a good adapter is
attached, the bq2415x enters charge mode. In charge mode, the IC has five control loops to regulate input
voltage, input current, charge current, charge voltage and device junction temperature. During the charging
process, all five loops are enabled and the one that is dominant takes control. The IC supports a precision Li-ion
or Li-polymer charging system for single-cell applications. Figure 27 (a) indicates a typical charge profile without
input current regulation loop. It is the traditional CC/CV charge curve, while Figure 27(b) shows a typical charge
profile when input current limiting loop is dominant during the constant current mode. In this case, the charge
current is higher than the input current so the charge process is faster than the linear chargers. The input voltage
threshold for DPM loop, input current limits, charge current, termination current, and charge voltage are all
programmable using I²C interface.
18
Submit Documentation Feedback
Product Folder Links :bq24157
Copyright © 2012, Texas Instruments Incorporated