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BQ77904 Datasheet(PDF) 17 Page - Texas Instruments |
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BQ77904 Datasheet(HTML) 17 Page - Texas Instruments |
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17 / 46 page  • Load removal detected only, VLD < VLDT OR • Overcurrent Recovery Timer, tCD_REC, expiration only OR • Overcurrent Recovery Timer expiration and load removal are detected. 8.3.2.7 Overcurrent Recovery Timer The timer expiration method activates an internal recovery timer as soon as the initial fault condition exceeds the OCD1/OCD2/SCD time. When the recovery timer reaches its limit, both CHG and DSG drivers are turned back on. If the combination option of timer expiration AND load removal is used, then the load removal condition is only evaluated upon expiration of the recovery timer, which can have an expiration period of tCD_REC. 8.3.2.8 Load Removal Detection The load removal detection feature is implemented with the LD pin (see Table 8-2). When no undervoltage fault and current fault conditions are present, the LD pin is held in an open-drain state. Once any UV, OCD1, OCD2, or SCD fault occurs and load removal is selected as part of the recovery conditions, a high impedance pull-down path to VSS is enabled on the LD pin. With an external load still present, the LD pin will be externally pulled high: It is internally clamped to VLDCLAMP and should also be resistor-limited through RLD externally to avoid conducting excessive current. If the LD pin exceeds VLDT, this is interpreted as a load present condition. When the load is eventually removed, the internal high-impedance path to VSS should be sufficient to pull the LD pin below VLDT for tLD_DEG. This is interpreted as a load removed condition and is one of the recovery mechanisms selectable for undervoltage and overcurrent faults. RLD LD pin Load Detect block RLD_INT VLDT bq77094/5 PACK- PACK+ LOAD When load detect is enabled, the LD pin is connected to Vss via the RLD_INT. The load, RLD and RLD_INT create a resister divider, which the load detect circuit is used to detect when the load is removed. Figure 8-3. Load Detection Circuit for Current Faults Recovery Table 8-2. Load State LD PIN LOAD STATE ≥ VLDT Load present < VLOT for tLD_DEG Load removed 8.3.2.9 Load Removal Detection in UV During a UV fault, only the DSG FET driver is turned off while the CHG FET driver remains on. When load removal is selected as part of the UV recovery condition, the active CHG FET driver would alter the resistor divider ratio of the load detection circuit. To ensure the load status can still be detected properly, it is required to increase the CHG FET external RGS value to about 3 MΩ. Refer to the Section 9.1.1.4 section for more detail. Note that if load removal is only selected for the current fault recovery (and is not used for UV recovery), it is not required to use a larger CHG FET RGS value. www.ti.com BQ77904, BQ77905 SLUSCM3K – APRIL 2020 – REVISED JULY 2020 Copyright © 2020 Texas Instruments Incorporated Submit Document Feedback 17 Product Folder Links: BQ77904 BQ77905 |
Similar Part No. - BQ77904_V04 |
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Similar Description - BQ77904_V04 |
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