BQ24152 Datasheet, PDF(20/38 Page) Texas Instruments – Fully Integrated Switch-Mode One-Cell Li-Ion Charger with Full USB Compliance and USB-OTG Support

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bq24152

SLUS847 â 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.

STAT Pin Boost Mode

During normal boosting process, the STAT pin behaves as a high impedance (open-drain) output. Under fault

conditions, a 128-Âµs pulse is sent out to notify the host.

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