SLUUCY8 December 2023 BQ77307
The BQ77307 integrates Overcurrent in Charge Protection (OCC) using a comparator that monitors the differential voltage across the SRP - SRN pins and triggers an OCC alert or fault when the voltage exceeds a programmable threshold VOCC. The VOCC threshold is programmable from 3 mV to 123 mV in 2-mV steps using the Protections:Current:Overcurrent in Charge Protection Threshold configuration register (threshold = 2 mV × register value - 1 mV). The OCC protection is enabled using the Settings:Protection:Enabled Protections A:[OCC] configuration bit.
The OCC circuitry triggers an alert signal when an overcurrent in charge event is first detected, then triggers a fault if it persists for a programmable detection delay, OCC_DLY, which can be set as shown below.
| Setting | Nominal Delay (ms) |
|---|---|
| 0 | Fastest (approximately 0.46 ms) |
| 1 to 64 | 1.22 ms to 20.435 ms in steps of 0.305 ms |
| 65 to 128 | 22.875 ms to 176.595 ms in steps of 2.44 ms |
| 129 to 192 | 181.475 ms to 488.915 ms in steps of 4.88 ms |
| 193 to 255 | 498.675 ms to 1103.795 ms in steps of 9.77 ms |
The delay is set by the Protections:Current:Overcurrent in Charge Protection Delay configuration register.
When an OCC fault is triggered, the device turns off the CHG FET if configured for autonomous FET control when Settings:Protection:CHG FET Protections A[OCC] is set. The device recovers after a programmable delay given by Protections:Current:Recovery Time , which can be set from 1 to 255 seconds in 1-second steps. A recovery time setting of 0 disables autonomous recovery, in which case recovery only occurs when the PROT_RECOVERY() subcommand is sent from the host with the [OCCREC] bit set. Continual retrying of time-based recovery can be avoided by using the Current Protection Latch feature.
| Status | Condition | Action |
|---|---|---|
| Normal | VSRP–VSRN ≤ setting selected by Protections:Current:Overcurrent in Charge Protection Threshold | Safety Alert A()[OCC] = 0. Clear current latch counter if no current protection fault occurs for 5 seconds. |
| Alert | VSRP–VSRN > setting selected by Protections:Current:Overcurrent in Charge Protection Threshold | Safety Alert A()[OCC] = 1 |
| Trip | VSRP–VSRN > setting selected by Protections:Current:Overcurrent in Charge Protection Threshold for Protections:Current:Overcurrent in Charge Protection Delay duration. | Safety Alert A()[OCC] = 0 Safety Status A()[OCC] = 1 Increment current latch counter. |
| Recovery | Safety Status A()[OCC] = 1 and VSRP–VSRN ≤ setting selected by Protections:Current:Overcurrent in Charge Protection Threshold for Protections:Current:Recovery Time duration. |
Safety Status A()[OCC] = 0 CHG FET can be re-enabled if conditions allow and it is not latched off. |
| Latch Limit | Current latch counter ≥ Protections:Current:Latch Limit | Safety Status A()[CURLATCH] = 1 CHG FET is latched off and not autonomously re-enabled. |