BQ24298_15 Datasheet, PDF (17/51 Pages) Texas Instruments – bq24298 I2C Controlled 3A Single Cell USB Charger With Narrow VDC Power Path Management and Adjustable Voltage USB OTG

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bq24298
SLUSC59 – APRIL 2015
The device provides soft-start when ramp up the system rail. When the system rail is below 2.2 V, the input
current limit is forced to 100mA. After the system rises above 2.2 V, the charger device sets the input current
limit set by the lower value between register and ILIM pin.
As a battery charger, the charger deploys a 1.5-MHz step-down switching regulator. The fixed frequency
oscillator keeps tight control of the switching frequency under all conditions of input voltage, battery voltage,
charge current and temperature, simplifying output filter design.
A type III compensation network allows using ceramic capacitors at the output of the converter. An internal saw-
tooth ramp is compared to the internal error control signal to vary the duty cycle of the converter. The ramp
height is proportional to the PMID voltage to cancel out any loop gain variation due to a change in input voltage.
In order to improve light-load efficiency, the device switches to PFM control at light load when battery is below
minimum system voltage setting or charging is disabled. During the PFM operation, the switching duty cycle is
set by the ratio of SYS and VBUS.
8.3.1.5 Boost Mode Operation from Battery
The device supports boost converter operation to deliver power from the battery to other portable devices
through USB port. The boost mode output current rating meets the USB On-The-Go 1-A output requirement. The
maximum output current is 1.5 A. The boost operation can be enabled if the following conditions are valid:
1. BAT above BATLOWV threshold (V_BATLOWV set by REG04[1])
2. VBUS less than V_BAT + V_SLEEP (in sleep mode)
3. Boost mode operation is enabled (OTG pin HIGH and REG01[5:4] = 10)
4. Thermistor Temperature is within boost mode temperature monitor threshold unless BHOT[1:0] is set to 11
(REG06[1:0]) to disable this monitor function
5. After 30ms delay from boost mode enable
In boost mode, the device employs a 1.5-MHz step-up switching regulator. Similar to buck operation, the device
switches from PWM operation to PFM operation at light load to improve efficiency.
During boost mode, the status register REG08[7:6] is set to 11, the VBUS output is 5 V and the output current
can reach up to 1 A or 1.5 A, selected via I²C (REG01[0]). In addition, the device provides adjustable boost
voltage from 4.55 V to 5.5 V by changing BOOSTV bits in REG06[7:4]
Any fault during boost operation, including VBUS over-voltage or over-current, sets the fault register REG09[6] to
1 and an INT is asserted.
8.3.2 Power Path Management
The device accommodates a wide range of input sources from USB, wall adapter, to car battery. The device
provides automatic power path selection to supply the system (SYS) from input source (VBUS), battery (BAT), or
both.
8.3.2.1 Narrow VDC Architecture
The device deploys Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by REG01[3:1]. Even with a fully depleted battery, the system is regulated above
the minimum system voltage (default 3.5 V).
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode),
and the system is 150 mV above the minimum system voltage setting. As the battery voltage rises above the
minimum system voltage, BATFET is fully on and the voltage difference between the system and battery is the
V_DS of BATFET. The status register REG08[0] goes high when the system is in minimum system voltage
regulation.
When the battery charging is disabled or terminated, and the battery voltage is above the minimum system
voltage setting, the system is always regulated at 70 mV above the battery voltage.
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