Narrow-VDC (NVDC) Power Path Management – Instant-On With No Battery or Deeply Discharged Battery – Battery Supplements System When Adapter is Fully-Loaded
8.4.1.1 System Voltage Regulation with Narrow VDC Architecture The bq25703A employs Narrow VDC architecture (NVDC) with BATFET separating system from battery. The minimum system voltage is set by MinSystemVoltage(). Even with a deeply depleted battery, the system is regulated above the minimum system voltage. When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode). As the battery voltage rises above the minimum system voltage, BATFET is fully on when charging or in supplement mode and the voltage difference between the system and battery is the VDS of BATFET. System voltage is regulated 160 mV above battery voltage when BATFET is off (no charging or no supplement current).
This figure shows the Narrow VDC (NVDC) topology. Here, the system bus (Vsys) is not connected directly to the adapter. It is connected to the output of the buck converter. Hence, NVDC operates only as a buck converter, both when NVDC charges the battery and when the battery supplements the adapter and provides power to the system. NVDC implementation reduces the switch-over period between the charging mode and the hybrid power mode. NVDC implementation allows the system to minimize the period of overloading the input power source when CPU is in Turbo Boost mode.
The advantage of using the NVDC system is that the overall system efficiency is better compared to the Hybrid Power Boost (HPB) charger. The system can be designed for a smaller voltage rating since the system has a lower Vin. The disadvantage is that the charger components’ size and power dissipation increases.
셀 갯수에 맞게 05/04h 에 전압을 설정한다. 다르게 보면 전압은 굳이 설정할 필요가 없어 보이고
CHRG_OK 이후에 03/02에 쓰면 충전이 시작 되는듯.
Upon POR, REG0x05/04() is by default set as 4192 mV for 1 s, 8400 mV for 2 s, 12592 mV for 3 s or 16800 mV for 4 s. After CHRG_OK, if host writes REG0x03/02() before REG0x05/04(), the charge will start after the write to REG0x03/02().If the battery is different from 4.2 V/cell, the host has to write to REG0x05/04() before REG0x03/02() for correct battery voltage setting. Writing REG0x05/04() to 0 will set REG0x05/04() to default value on CELL_BATPRESZ pin, and force REG0x03/02() to zero to disable charge.