SLUSA27 – MARCH 2010
Start T15 min
T 15 min Active ?
Start T32 sec
Stop T15 min
Any I 2 C Write -
T 15 min
T 32 sec Expired ?
Host Should Reset
T 32 sec Timer
Figure 27. Timer Flow Chart for bq24153/6/8
USB Friendly Boot-Up Sequence
Prior to power up if the host continus to write the TMR_RST bit to 1, to stay in 32 second mode, on power up the
charger enters normal charge mode (using the desired control bits). If not in 32 second mode at power up, the
charge will operate with default bit values, in 15 minute mode, until the host updates the control registers.
If the battery voltage is above the VLOWV threshold while in 15 minute mode, the charger will be in the high
impedance state. 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
The input current sensing circuit and control loop are integrated into the IC. When operating in 15 minute mode,
for bq24153/8, the OTG pin sets the input current limit to 100mA for a logic low and 500mA for a logic high,
whereas the bq24156 defaults to 500mA. In 32 second mode, the input current limit is set by the programmed
control bits in register 01H.
Thermal Regulation and Protection
To prevent overheat of the chip during the charging process, the IC monitors the junction temperature, TJ, of the
die and begins to taper down the charge current once TJ reaches the thermal regulation threshold, TCF. The
charge current is reduced to zero when the junction temperature increases approximately 10°C above TCF. In
any state, if TJ exceeds TSHTDWN, the IC suspends charging. In thermal shutdown mode, PWM is turned off and
all timers are frozen. Charging resumes when TJ falls below TSHTDWN by approximately 10°C.
Input Voltage Protection in Charge Mode
The IC enters the low-power sleep mode if the voltage on VBUS pin falls below sleep-mode entry threshold,
VCSOUT+VSLP, and VBUS is higher than the bad adaptor detection threshold, VIN(MIN). This feature prevents draining
the battery during the absence of VBUS. During sleep mode, both the reverse blocking switch Q1 and PWM are
Copyright © 2010, Texas Instruments Incorporated
Submit Documentation Feedback
Product Folder Link(s): bq24153 bq24156 bq24158