SLUUCA6 October 2021 BQ27Z746
The device supports trickle charging a cell at very low voltages. This is known as zero volt charging (ZVCHG). When ZVCHG is enabled, the device connects the gate of the CHG FET to the PACK pin to turn it on when the cell voltage is otherwise too low. ZVCHG is only enabled in the presence of a charger as determined by the PACK pin voltage. While ZVCHG is enabled, the FET driver to the gate of the CHG FET is disabled (reflected by OperationStatus()[CHG]). ZVCHG is disabled for the same charge disable conditions as described above, as well as for any protections that disable the CHG FET.
When the device boots up, the DSG FET is off and the CHG FET is on due to ZVCHG. The device performs very fast ADC measurements of cell and PACK voltage to determine if ZVCHG should remain enabled to prevent the device from possibly experiencing a power-on reset due to a low cell voltage. If the conditions to enable ZVCHG are not present, the CHG FET is turned off by disabling ZVCHG to ensure no current flows during the initial measurements for open-circuit voltage (OCV).
Status | Condition | Action |
---|---|---|
Activate | Voltage() < ZVCHG Exit Threshold
AND Pack Pin Voltage ≥ ZVCHG PACK Threshold |
OperationStatus()[ZVCHG] = 1 OperationStatus()[CHG] = 0 |
Exit | Voltage() ≥ ZVCHG Exit Threshold
OR Pack Pin Voltage < ZVCHG PACK Threshold |
OperationStatus()[ZVCHG] = 0 OperationStatus()[CHG] = 1 |
Class | Subclass | Name | Type | Min | Max | Default | Unit |
---|---|---|---|---|---|---|---|
Settings | AFE | ZVCHG Exit Threshold | I2 | 0 | 2000 | 2000 | mV |
Settings | AFE | ZVCHG PACK Threshold | I2 | 0 | 2000 | 1500 | mV |