SLUUCJ0 November 2023 BQ76907
The BQ76907 integrates two Overcurrent in Discharge Protections (OCD1, OCD2) using a comparator that monitors the differential voltage across the SRN - SRP pins and triggers an OCD1 or OCD2 alert or fault when the voltage exceeds a programmable threshold VOCD1 and VOCD2, respectively. The VOCD1/2 thresholds are programmable from 4 mV to 200 mV in 2 mV steps using the Protections:Current:Overcurrent in Discharge 1 Protection Threshold and Protections:Current:Overcurrent in Discharge 2 Protection Threshold configuration registers. These two protections operate identically, but can have independent threshold and delay settings. The OCD1 and OCD2 protections are enabled using the Settings:Protection:Enabled Protections A:[OCD1] and [OCD2] configuration bits.
The OCD1/2 circuitry triggers an alert signal when an overcurrent in discharge event is first detected, then triggers a fault if it persists for a programmable detection delay, OCD1_DLY or OCD2_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 Discharge 1 Protection Delay and Protections:Current:Overcurrent in Discharge 2 Protection Delay configuration registers.
When an OCD fault is triggered, the device turns off the DSG FET if configured for autonomous FET control in Settings:Protection:DSG FET Protections A[OCD1, OCD2]. The device recovers after a programmable delay given by Protections:Current:Recovery Time, which can be set from 1-sec to 255-sec in 1-sec steps. A recovery time setting of 0 disables autonomous recovery, in which case recovery only occurs when the PROT_RECOVERY() command is sent from the host with the appropriate [OCD1REC] or [OCD2REC] bit set. Continual retrying of time-based recovery can be avoided by using the Current Protection Latch feature.
| Status | Condition | Action |
|---|---|---|
| Normal | VSRN–VSRP ≤ setting selected by Protections:Current:Overcurrent in Discharge 1 Protection Threshold | Safety Alert A()[OCD1] = 0. Clear current latch counter if no current protection fault occurs for 5 seconds. |
| Normal | VSRN–VSRP ≤ setting selected by Protections:Current:Overcurrent in Discharge 2 Protection Threshold | Safety Alert A()[OCD2] = 0. Clear current latch counter if no current protection fault occurs for 5 seconds. |
| Alert | VSRN–VSRP > setting selected by Protections:Current:Overcurrent in Discharge 1 Protection Threshold | Safety Alert A()[OCD1] = 1 |
| Alert | VSRN–VSRP > setting selected by Protections:Current:Overcurrent in Discharge 2 Protection Threshold | Safety Alert A()[OCD2] = 1 |
| Trip | VSRP–VSRN > setting selected by Protections:Current:Overcurrent in Discharge 1 Protection Threshold for Protections:Current:Overcurrent in Discharge 1 Protection Delay duration. | Safety Alert A()[OCD1] = 0 Safety Status A()[OCD1] = 1 Increment current latch counter. |
| Trip | VSRP–VSRN > setting selected by Protections:Current:Overcurrent in Discharge 2 Protection Threshold for Protections:Current:Overcurrent in Discharge 2 Protection Delay duration. | Safety Alert A()[OCD2] = 0 Safety Status A()[OCD2] = 1 Increment current latch counter. |
| Recovery | Safety Status A()[OCD1] = 1 and VSRN–VSRP ≤ setting selected by Protections:Current:Overcurrent in Discharge 1 Protection Threshold for Protections:Current:Recovery Time duration. | Safety Status A()[OCD1] = 0 DSG FET can be re-enabled if conditions allow and it is not latched off. |
| Recovery | Safety Status A()[OCD2] = 1 and VSRN–VSRP ≤ setting selected by Protections:Current:Overcurrent in Discharge 2 Protection Threshold for Protections:Current:Recovery Time duration. | Safety Status A()[OCD2] = 0 DSG 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 DSG FET is latched off and not autonomously re-enabled. |