BQ24298_15 Datasheet, PDF (16/51 Pages) Texas Instruments – bq24298 I2C Controlled 3A Single Cell USB Charger With Narrow VDC Power Path Management and Adjustable Voltage USB OTG

bq24298
SLUSC59 – APRIL 2015
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Feature Description (continued)
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 (15 µA typical) from VBUS during HIZ state. The battery powers up the system
when the device is in HIZ.
8.3.1.3.2 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 (3.8 V typical) when pulling I_BADSRC (30 mA typical) (poor source detection)
Once the input source passes all the conditions above, the status register REG08[2] goes high and the PG pin
(bq24298) 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.
8.3.1.3.3 Input Current Limit Detection
After the PG is LOW (bq24298)or 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 bq24298 sets input current limit through PSEL and OTG pins. 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 addition, host can write to REG00[2:0] to change the input current limit.
8.3.1.3.4 PSEL/OTG Pins Set Input Current Limit
The bq24298 has PSEL pin which directly takes the USB PHY device output to decide whether the input is USB
host or charging port.
Table 2. bq24298 Input Current Limit Detection
PSEL
HIGH
HIGH
LOW
OTG
LOW
HIGH
—
INPUT CURRENT LIMIT
100 mA
500 mA
3A
REG08[7:6]
01
01
10
8.3.1.3.5 HIZ State with 100mA USB Host
In battery charging spec, the good battery threshold is the minimum charge level of a battery to power up the
portable device successfully. When the input source is 100-mA USB host, and the battery is above bat-good
threshold (V_BATGD), the device follows battery charging spec and enters high impedance state (HIZ). In HIZ state,
the device is in the lowest quiescent state with REGN LDO and the bias circuits off. The charger device sets
REG00[7] to 1, and the VBUS current during HIZ state will be less than 30 µA. 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.
In default mode, the charger IC will reset REG00[7] back to 0 when input source is removed. When another
source plugs in, the charger IC will run detection again, and update the input current limit.
8.3.1.3.6 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 100 mA.
After the detection is completed, REG07[7] will return to 0 by itself and new input current limit is set based on
PSEL/OTG (bq24298).
8.3.1.4 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.
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