BQ25895_16 Datasheet, PDF (20/67 Pages) Texas Instruments – Adjustable Voltage 3.1-A Boost Operation

bq25895
SLUSC88A – MARCH 2015 – REVISED MAY 2016
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8.2.5 Boost Mode Operation from Battery
The device supports boost converter operation to deliver power from the battery to other portable devices
through PMID pin. The boost mode output current rating supports maximum output current up to 3.1 A to charge
smartphone and tablet at fast charging rate. The boost operation can be enabled if the conditions are valid:
1. BAT above BAT_LOWV
2. VBUS less than BAT+V_SLEEP (in sleep mode)
3. Boost mode operation is enabled (OTG pin HIGH and OTG_CONFIG bit =1)
4. Voltage at TS (thermistor) pin is within range configured by Boost Mode Temperature Monitor as configured
by BHOT and BCOLD bits
5. After 30 ms delay from boost mode enable
In boost mode, the device employs a 500 KHz or 1.5 MHz (selectable using BOOST_FREQ bit) step-up
switching regulator based on system requirements. To avoid frequency change during boost mode operations,
write to boost frequency configuration bit (BOOST_FREQ) is ignored when OTG_CONFIG is set.
During boost mode, the status register VBUS_STAT bits is set to 111, the VBUS output is 5V by default
(selectable via BOOSTV register bits). The boost output is maintained when BAT is above V_{OTG_BAT} threshold
8.2.6 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.
8.2.6.1 Narrow VDC Architecture
The device deploys Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by SYS_MIN bits. 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 regulated 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 VSYS_STAT bit goes high when the system is in minimum system voltage
regulation.
4.4
Minimum System Voltage
SYS (Charge Disabled)
4.2
SYS (Charge Enabled)
4
3.8
3.6
3.4
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3
BAT (V)
D011
Figure 10. V(SYS) vs V(BAT)
8.2.6.2 Dynamic Power Management
To meet maximum current limit in USB spec and avoid over loading the adapter, the device features Dynamic
Power Management (DPM), which continuously monitors the input current and input voltage. When input source
is over-loaded, either the current exceeds the input current limit (IINLIM or IDPM_LIM) or the voltage falls below
the input voltage limit (VINDPM). The device then reduces the charge current until the input current falls below
the input current limit and the input voltage rises above the input voltage limit.
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