SLUS756D September   2007  – June 2026 BQ24751A

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
    1. 4.1 Terminal Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 Recommended Operating Conditions
    3. 5.3 Package Thermal Data
    4. 5.4 Electrical Characteristics
    5. 5.5 Typical Charateristics
  7. 6 Detailed Description
    1. 6.1  Functional Block Diagram
    2. 6.2  Battery Voltage Regulation
    3. 6.3  Battery Current Regulation
    4. 6.4  Input Adapter Current Regulation
    5. 6.5  Adapter Detect and Power Up
    6. 6.6  Enable and Disable Charging
    7. 6.7  System Power Selector
    8. 6.8  Battery Learn Cycles
    9. 6.9  Automatic Internal Soft-Start Charger Current
    10. 6.10 Converter Operation
    11. 6.11 Synchronous and Non-Synchronous Operation
    12. 6.12 High Accuracy IADAPT Using Current Sense Amplifier (CSA)
    13. 6.13 Input Overvoltage Protection (ACOV)
    14. 6.14 Input Undervoltage Lock Out (UVLO)
    15. 6.15 Battery Overvoltage Protection
    16. 6.16 Battery Shorted (Battery Undervoltage) Protection
    17. 6.17 Charge Overcurrent Protection
    18. 6.18 Thermal Shutdown Protection
    19. 6.19 Adapter Detected Status Register ( ACGOOD Pin)
    20. 6.20 Input Over-Power Protection (ACOP)
      1. 6.20.1 Conditions for ACOP Latch Off:
  8. 7 Application Information
    1. 7.1 Input Capacitance Calculation
    2. 7.2 PCB Layout Design Guideline
  9. 8 Device and Documentation Support
    1. 8.1 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

6.16 Battery Shorted (Battery Undervoltage) Protection

The bq24751A has a BAT SHORT comparator monitoring the output battery voltage (BAT). If the voltage falls below 2.9 V per cell (5.8 V for 2 cells, 8.7 V for 3 cells, 11.6 V for 4 cells), a battery-short status is detected. Below the BAT_SHORT threshold, the charger reduces the charge current to 1/8th of the programmed charging current (0.1×SRSET/VDAC)/8 = C/8 down to zero volts on BAT pin.. This lower current is used as a pre-charge current for over-discharged battery packs. Above the BAT_SHORT threshold (plus hysteresis, the charge current resumes at the programmed value (0.1×SRSET/VDAC).

The BAT_SHORT comparator also serves as a depleted-battery alarm during a LEARN cycle. If the selector is in a LEARN cycle, and the battery voltage falls bellow the BAT_SHORT threshold, the selector disconnects the battery from the system and connects the adapter to the system in order to protect the battery pack. If battery voltage increases, and LEARN is still logic high, then the selector disconnects the adapter from the system and reconnects the battery to the system.