ZHCS692C October 2010 – October 2015
PRODUCTION DATA.
The bq3055 device measures the voltage, temperature, and current to determine battery capacity and state-of-charge (SOC). The bq3050 monitors charge and discharge activity by sensing the voltage across a small value resistor (5 mΩ to 20 mΩ, typical) between the SRP and SRN pins and in series with the battery. By integrating charge passing through the battery, the battery’s SOC is adjusted during battery charge or discharge. Measurements of OCV and charge integration determine chemical SOC.
The Qmax values are taken from a cell manufacturers' data sheet multiplied by the number of parallel cells, and is also used for the value in Design Capacity. It uses the OCV and Qmax value to determine StateOfCharge() on battery insertion, device reset, or on command. The FullChargeCapacity() is reported as the learned capacity available from full charge until Voltage() reaches the EDV0 threshold. As Voltage() falls below the Shutdown Voltage for Shutdown Time and has been out of SHUTDOWN mode for at least Shutdown Time, the PF Flags1 () [VSHUT] bit is set. For additional details, see bq3055 Technical Reference Manual (SLUU440).
Fuel gauging is derived from the Compensated End of Discharge Voltage (CEDV) method, which uses a mathematical model to correlate remaining state of charge (RSOC) and voltage near to the end of discharge state. This requires a full-discharge cycle for a single-point FCC update. The implementation models cell voltage (OCV) as a function of battery SOC, temperature, and current. The impedance is also a function of SOC and temperature, which can be satisfied by using seven parameters: EMF, C0, R0, T0, R1, TC, and C1.
The bq3055 fully integrates the system oscillators and does not require any external components to support this feature.
The bq3055 checks the PRES pin periodically (1 s). If PRES input is pulled to ground by the external system, the bq3055 detects this as system present.
In a 2-cell configuration, VC1 is shorted to VC2 and VC3. In a 3-cell configuration, VC1 is shorted to VC2.
The device supports cell balancing by bypassing the current of each cell during charging or at rest. If the device's internal bypass is used, up to 10 mA can be bypassed and multiple cells can be bypassed at the same time. Higher cell balance current can be achieved by using an external cell balancing circuit. In external cell balancing mode, only one cell at a time can be balanced.
The cell balancing algorithm determines the amount of charge needed to be bypassed to balance the capacity of all cells.
When internal cell balancing is configured, the cell balance current is defined by the external resistor RVC at the VCx input. See Figure 4.
When external cell balancing is configured, the cell balance current is defined by RB. See Figure 5. Only one cell at a time can be balanced.
The bq3055 supports a wide range of battery and system protection features that can easily be configured. The primary safety features include:
The secondary safety features of the bq3055 can be used to indicate more serious faults through the FUSE pin. This pin can be used to blow an in-line fuse to permanently disable the battery pack from charging or discharging. The secondary safety protection features include:
The bq3055 charge control features include:
The bq3055 uses the CEDV algorithm to measure and calculate the available capacity in battery cells. The bq3055 accumulates a measure of charge and discharge currents and compensates the charge current measurement for the temperature and state-of-charge of the battery. The bq3055 estimates self-discharge of the battery and also adjusts the self-discharge estimation based on temperature. See the bq3055 Technical Reference Manual (SLUU440) for further details.
The bq3055 offers limited lifetime data logging for the following critical battery parameters:
The bq3055 supports three power modes to reduce power consumption: