BQ24295 Datasheet, PDF (24/45 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

bq24295
SLUSBC1 – SEPTEMBER 2013
www.ti.com
Non-Standard
Adapter
Divider 1
Divider 2
Divider 3
Table 3. bq24295 Non-Standard Adapter Detection
D+ Threshold
D- Threshold
V_{adpt1_lo} < V_D+ < V_{adpt1_hi}
For VBUS=5V, typical range 2.4V < V_D+ < 3.1V
V_{adpt2_lo} < V_D+ < V_{adpt2_hi}
For VBUS=5V, typical range 0.85V < V_D+ < 1.5V
V_{adpt3_lo} < V_D+ < V_{adpt3_hi}
For VBUS=5V, typical range 2.4V > V_D+ or V_D+ >
3.1V
V_{adpt1_lo} > V_D- or V_D- < V_{adpt1_hi}
For VBUS=5V, typical range 2.4V > V_D- or V_D- > 3.1V
NA
V_{adpt3_lo} < V_D- < V_{adpt3_hi}
For VBUS=5V, typical range 2.4V < V_D- < 3.1V
Input
Current
Limit
2A
2A
1A
Force Input Current Limit Detection
While adapter is plugged-in, the host can force the charger device to run input current limit detection by setting
REG07[7]=1 or when watchdog timeout. During the forced detection, the input current limit is set to 100mA. After
the detection is completed, REG07[7] will return to 0 by itself and new input current limit is set based on D+/D-.
Converter Power-Up
After the input current limit is set, the converter is enabled and the HSFET and LSFET start switching. If battery
charging is disabled, BATFET turns off. Otherwise, BATFET stays on to charge the battery.
The device provides soft-start when ramp up the system rail. When the system rail is below 2.2V, the input
current limit is forced to 100mA. After the system rises above 2.2V, 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 1.5MHz 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.
Low Power HIZ State
The host can configure the converter to go into HIZ State by setting EN_HIZ (REG00[7]) to 0. The device is in
the lowest quiescent state with REGN LDO and the bias circuits off, the VBUS current during HIZ state will be
less than 30µA while the system is supplied by the battery. Once the charger device enters HIZ state in host
mode, it stays in HIZ until the host writes REG00[7]=0. When the processor host wakes up, it is recommended to
first check if the charger is in HIZ state.
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.
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 3.5V).
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode),
and the system is 150mV 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.
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