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BQ24152 Datasheet(PDF) 20 Page - Texas Instruments

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Part No. BQ24152
Description  Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support
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Maker  TI [Texas Instruments]
Homepage  http://www.ti.com
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BQ24152 Datasheet(HTML) 20 Page - Texas Instruments

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STAT Pin Boost Mode
bq24152
SLUS847 – JUNE 2008 ...................................................................................................................................................................................................... www.ti.com
In boost mode, the input N-MOSFET (Q1) prevents battery discharge when VBUS pin is overloaded.
Cycle-by-cycle current limit is sensed through the internal sense MOSFET for Q3. The threshold for Q3 is set to
a nominal 1-A peak current. The upper-side MOSFET (Q2) also has a current limit that decides if the PWM
Controller will operate in synchronous or non-synchronous mode. This threshold is set to 75 mA and it turns off
the high-side N-channel MOSFET (Q2) before the current reverses, preventing the battery from charging.
Synchronous operation is used when the current of the high-side MOSFET is greater than 75 mA to minimize
power losses.
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 bq24152 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 once the
inductor current is less than 75 mA; and the PWM is turned back on only when the voltage at PMID pin drops to
about 99.5% of the 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 bq24152 starts a 32-second timer that can be reset by host through I2C
interface. Writing "1" to reset bit of TMR_RST in the control register resets the 32-second timer and TMR_RST is
automatically set to "0" after the 32-second timer is reset. To keep in boost mode, the host must reset the
32-second timer repeatedly. Once the 32-second timer expires, the bq24152 turns off the boost converter,
enunciate the fault pulse in STAT pin and set fault status bits in status register. Fault condition is cleared by POR
or host control.
Protection in Boost Mode
Output Overvoltage Protection
The bq24152 provides a built-in overvoltage protection to protect the device and other components against
damage if the VBUS voltage goes too high. When an overvoltage condition is detected, the bq24152 turns off the
PWM converter, reset OPA_MODE bit to 0, sets fault status bits, and sends out fault pulse in STAT pin. Once
VBUS drops to the normal level, the boost starts after host sets OPA_MODE to "1", or the OTG pin remains in
active status.
Output Overload Protection
The bq24152 provides a built-in overload protection to prevent the device and battery from damage when VBUS
is over loaded. Once over load condition is detected, Q1 operates in linear mode to limit the output current while
VPMID keeps in voltage regulation. If the overload condition lasts for more than 30ms, the overload fault is
detected. When an overload condition is detected, the bq24152 turns off the PWM converter, reset OPA_MODE
bit to 0, sets fault status bits, and sends out fault pulse in STAT pin. The boost will not start until the host clears
the fault register.
Battery Voltage Protection
During boosting, when battery voltage is above the battery overvoltage threshold, V(BATMX), or below the minimum
battery voltage threshold, V(BAT)min, the bq24152 turns off the PWM converter, reset OPA_MODE bit to 0, sets
fault status bits, and sends out fault pulse in STAT pin. Once battery voltage goes back to the normal level, the
boost starts after host sets OPA_MODE to "1", or the OTG pin remains in active status.
During normal boosting process, the STAT pin behaves as a high impedance (open-drain) output. Under fault
conditions, a 128-
µs pulse is sent out to notify the host.
20
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Copyright © 2008, Texas Instruments Incorporated
Product Folder Link(s): bq24152


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