BQ24295 Datasheet, PDF (22/45 Pages) Texas Instruments – I2C Controlled 3A Single Cell USB Charger

bq24295
SLUSBC1 – SEPTEMBER 2013
www.ti.com
Integrated Control to Switch Between USB Charge Mode and Boost Mode
The device features integrated control to switch between charge mode and boost mode by monitoring VBUS
voltage. When VBUS is higher than VBAT+V_SLEEP , the RBFET is enabled and charge mode is enabled. When
VBUS power source is removed, the RBFET is automatically turn off to isolate VBUS from PMID. The boost
mode is started when the conditions described above are met.
Power Up from DC Source
When the DC source plugs in, the charger device checks the input source voltage to turn on REGN LDO and all
the bias circuits. It also checks the input current limit before starts the buck converter.
REGN LDO
The REGN LDO supplies internal bias circuits as well as the HSFET and LSFET gate drive. The LDO also
provides bias rail to TS external resistors. The pull-up rail of STAT can be connected to REGN as well.
The REGN is enabled when all the conditions are valid.
1. VBUS above V_{VBUS_UVLOZ}
2. VBUS above V_BAT + V_SLEEPZ in buck mode or VBUS below V_BAT + V_SLEEP in boost mode
3. After typical 220ms delay (100ms minimum) is complete
If one of the above conditions is not valid, the device is in high impedance mode (HIZ) with REGN LDO off. The
device draws less than I_VBUS (15µA typical) from VBUS during HIZ state. The battery powers up the system when
the device is in HIZ.
Input Source Qualification
After REGN LDO powers up, the device checks the current capability of the input source. The input source has
to meet the following requirements to start the buck converter.
1. VBUS voltage below V_ACOV (not in VBUS over-voltage)
2. VBUS voltage above V_BADSRC (3.8V typical) when pulling I_BADSRC (30mA typical) (poor source detection)
Once the input source passes all the conditions above, the status register REG08[2] goes high and the PG pin
goes low. An INT is asserted to the host.
If the device fails the poor source detection, it will repeat the detection every 2 seconds.
Input Current Limit Detection
The USB ports on personal computers are convenient charging source for portable devices (PDs). If the portable
device is attached to a USB host, the USB specification requires the portable device to draw limited current
(500mA in USB 2.0, and 150mA/900mA in USB 3.0). If the portable device is attached to a charging port, it is
allowed to draw up to 3A.
After the REG08[2] goes HIGH, the charger device always runs input current limit detection when a DC source
plugs in unless the charger is in HIZ during host mode.
The bq24295 follows Battery Charging Specification 1.2 (BC1.2) to detect input source through USB D+/D- lines.
After the input current limit detection is done, the detection result is reported in VBUS_STAT registers
(REG08[7:6]) and input current limit is updated in IINLIM register (REG00[2:0]). In additon, host can write to
REG00[2:0] to change the input current limit.
D+/D– Detection Sets Input Current Limit
The bq24295 contains a D+/D– based input source detection to program the input current limit. The D+/D-
detection has three steps: data contact detect (DCD), primary detection, and non-standard adapter detection.
When the charging source passes data contact detect, the device would proceed to run primary detection.
Otherwise the charger would proceed to run non-standard adapter detection.
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