SLUUCH2 March 2021 BQ40Z50-R2
During normal operation, the battery-impedance profile compensation of the Impedance Track algorithm can provide more accurate full-charge and remaining state-of-charge information if the typical load type is known. The two selectable options are constant current (Load Mode = 0) and constant power (Load Mode = 1).
To compensate for the I × R drop near the end of discharge, the BQ40Z50-R4 must be configured for the current (or power) that will flow in the future. While it cannot be exactly known, the BQ40Z50-R4 can use load history, such as the average current of the present discharge, to make a sufficiently accurate prediction.
The BQ40Z50-R4 can be configured to use several methods of this prediction by setting the Load Select value. Because this estimate has only a second-order effect on remaining capacity accuracy, different measurement-based methods (methods 0–3 and method 7) result in only minor differences in accuracy. However, methods 4–6, where an estimate is arbitrarily user-assigned, can result in a significant error if a fixed estimate is far from the actual load. For highly variable loads, selection 7 provides the most conservative estimate and is preferable.
| Constant Current (Load Mode = 0) | Constant Power (Load Mode = 1) | |
| 0 = | Avg I Last Run | Avg P Last Run |
| 1 = | Present average discharge current | Present average discharge power |
| 2 = | Current() | Current() × Voltage() |
| 3 = | AverageCurrent() | AverageCurrent() × average Voltage() |
| 4 = | Design Capacity/5 | Design Capacity cWh/5 |
| 5 = | AtRate() (mA) | AtRate() (cW) |
| 6 = | User Rate-mA | User Rate-mW |
| 7 = | Max Avg I Last Run (default) | Max Avg P Last Run |
To take into account pulsed loads while calculating remaining capacity until Term Voltage threshold is reached, the BQ40Z50-R4 monitors not only the average load but also the short load spikes. The maximum voltage deviation during a load spike is continuously updated during discharge and stored in Delta Voltage.
The BQ40Z50-R4 allows an amount of capacity to be reserved in either mAh (Reserve Cap-mAh, Load Mode = 0) or cWh (Reserve Cap-cWh, Load Mode = 1) units between the point where the RemainingCapacity() function reports zero capacity and the absolute minimum battery stack voltage, Term Voltage. This enables a system to report zero energy, but still have enough reserve energy to perform a controlled shutdown or provide an extended sleep period for the host system.
The reserve capacity is compensated at the present discharge rate as selected by Load Select.
The PS No Load Res Cap threshold is programmed to a value in mAh based on how much capacity to reserve for powering the RTC for a period of time after RSOC is 0%.
| Class | Subclass | Name | Format | Size in Bytes | Min | Max | Default | Unit |
|---|---|---|---|---|---|---|---|---|
| Power | Shutdown | PS No Load Res Cap | Unsigned Int | 2 | 0 | 32767 | 0 | mAh |
There is no requirement to change Term Voltage, and this can remain set to the minimum system operation voltage.
The BQ40Z50-R4 forces RemainingCapacity() to 0 mAh when the battery stack voltage reaches the Term Voltagefor a period of Term V Hold Time. If IT Gauging Configuration[CELL_TERM] = 1, the battery can terminate based on cell voltage or battery stack voltage. When the cell-based termination is used, the Term Min Cell V threshold is checked for the termination condition. The cell-based termination can provide an option to enable the gauge to reach 0% before the device triggers CUV for a pack imbalance.
| Class | Subclass | Name | Format | Size in Bytes | Min Value | Max Value | Default Value | Unit |
|---|---|---|---|---|---|---|---|---|
| Gas Gauging | IT Cfg | Term V Hold Time | Unsigned Int | 1 | 0 | 255 | 1 | s |