BQ25890H Datasheet, PDF (21/66 Pages) Texas Instruments – I2C Controlled Single Cell 5-A Fast Charger

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BQ25890H
SLUSCC5 – SEPTEMBER 2016
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 USB port. The boost mode output current rating meets the USB On-The-Go 500 mA (BOOST_LIM bits =
000) output requirement. The maximum output current is up to 2.4 A. 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) and the output current can reach up to 2.4 A, selected via I²C
(BOOST_LIM 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)
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