BQ24140_14 Datasheet, PDF (22/39 Pages) Texas Instruments – Integrated Dual-Input Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

bq24140
SLUSAO5 – OCTOBER 2011
www.ti.com
Battery detection during power-up
The bq24140 also has a unique battery detection scheme during the start up of the charger. At power up, if the
timer is in 15-minute mode, bq24140 will start a 262ms timer when exiting from short circuit mode to PWM
charge mode. If the battery voltage is charged to recharge threshold (V_OREG–V_RCH) and the 262ms timer has not
expired yet, or battery voltage is above output OVP threshold during short-circuit mode, bq24140 will consider
the battery is not present; then stop charging and go to high impedance mode immediately. However, if the
262ms timer has expired before the recharge threshold is reached, the charging process will continue as normal.
HIGH-SIDE LED DRIVER
The LED pin is a high-side LED driver. This LED function needs to run from the battery and the expected output
current can be programmed through I²C. There are 2 bits for programming the output current from the LED pin.
In addition, there is extra programmability for the LED function. Since there is only one LED driver used by both
the VIN and VBUS charger cores, there is only one LED register that can be accessed through the addresses
6AH and 6BH. When one of the two addresses is written, the settings for both cores will be set. Refer to the
Register Description Section for details on the LED programmable timings and current options.
BOOST CONVERTER OPERATION
The bq24140 support USB-OTG for the VBUS pin when OTG mode is enabled. In this configuration, the battery
voltage is boosted to 5.05V (±3%). The maximum output current for the boost converted is increased to 650mA
minimum current.
Boost Start Up
To prevent the inductor saturation and limit the inrush current, a soft-start control is applied during the boost start
up.
PFM Mode at Light Load
In boost mode, the IC operates in pulse skipping mode (PFM mode) to reduce the power loss and improve the
converter efficiency at light load condition. During boosting, the PWM converter is turned off if the inductor
current falls below than 200mA. The PWM is turned back on only when the voltage at PMID pin drops to 99.5%
of the typical rated output voltage. A unique pre-set circuit is used to make the smooth transition between PWM
and PFM mode.
Safety Timer in Boost Mode
At the beginning of boost operation, the IC starts a 32-second timer that is reset by the host using the I²C
interface. Writing “1” to reset bit of TMR_RST in control register will reset the 32-second timer and TMR_RST is
automatically set to “0” after the 32-second timer is reset. Once the 32-second timer expires, the IC turns off the
boost converter, enunciates the fault pulse from the STAT pin and sets fault status bits in the status register. The
fault condition is cleared by POR or host control.
Charge Status Output, STAT Pin
The STAT pin is used to indicate operation conditions for bq24140. STAT is pulled low during charging when
EN_STAT bit in control register (00H) is set to “1”. Under other conditions, STAT pin behaves as a high
impedance (open-drain) output. Under fault conditions, a 128-μs pulse will be sent out to notify the host. The
status of STAT pin at different operation conditions is summarized in Table 1. The STAT pin can be used to drive
an LED or communicate to the host processor.
Table 1. STAT Pin Summary
CHARGE STATE
Charge in progress and EN_STAT = 1
Other normal conditions
Charge mode faults and input not in HiZ
Boost mode faults and input not in HiZ
VIN Present bit change (H→L or L→H) regardless of HiZ status
VBUS Present bit change (H→L or L→H) regardless of HiZ status
STAT
Low
Open-Drain
128 µs pulse, then open-drain
128 µs pulse, then open-drain
128 µs pulse, then normal per above cases
128 µs pulse, then normal per above cases
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