SLUSAL0C September   2011  – January 2020 BQ24725A

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 SMBus Interface
    4. 8.4 Device Functional Modes
      1. 8.4.1  Adapter Detect and ACOK Output
      2. 8.4.2  Adapter Over Voltage (ACOVP)
      3. 8.4.3  System Power Selection
      4. 8.4.4  Battery LEARN Cycle
      5. 8.4.5  Enable and Disable Charging
      6. 8.4.6  Automatic Internal Soft-Start Charger Current
      7. 8.4.7  High Accuracy Current Sense Amplifier
      8. 8.4.8  Charge Timeout
      9. 8.4.9  Converter Operation
      10. 8.4.10 Continuous Conduction Mode (CCM)
      11. 8.4.11 Discontinuous Conduction Mode (DCM)
      12. 8.4.12 Input Over Current Protection (ACOC)
      13. 8.4.13 Charge Over Current Protection (CHGOCP)
      14. 8.4.14 Battery Over Voltage Protection (BATOVP)
      15. 8.4.15 Battery Shorted to Ground (BATLOWV)
      16. 8.4.16 Thermal Shutdown Protection (TSHUT)
      17. 8.4.17 EMI Switching Frequency Adjust
      18. 8.4.18 Inductor Short, MOSFET Short Protection
    5. 8.5 Register Maps
      1. 8.5.1 Battery-Charger Commands
      2. 8.5.2 Setting Charger Options
        1. Table 3. Charge Options Register (0x12H)
      3. 8.5.3 Setting the Charge Current
        1. Table 4. Charge Current Register (0x14H), Using 10mΩ Sense Resistor
      4. 8.5.4 Setting the Charge Voltage
        1. Table 5. Charge Voltage Register (0x15H)
      5. 8.5.5 Setting Input Current
        1. Table 6. Input Current Register (0x3FH), Using 10mΩ Sense Resistor
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Applications
      1. 9.2.1 Typical System with Two NMOS Selector
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Negative Output Voltage Protection
          2. 9.2.1.2.2 Reverse Input Voltage Protection
          3. 9.2.1.2.3 Reduce Battery Quiescent Current
          4. 9.2.1.2.4 Inductor Selection
          5. 9.2.1.2.5 Input Capacitor
          6. 9.2.1.2.6 Output Capacitor
          7. 9.2.1.2.7 Power MOSFETs Selection
          8. 9.2.1.2.8 Input Filter Design
          9. 9.2.1.2.9 BQ24725A Design Guideline
        3. 9.2.1.3 Application Curves
      2. 9.2.2 Simplified System without Power Path
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
        3. 9.2.2.3 Application Curves
    3. 9.3 System Examples
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Third-Party Products Disclaimer
    2. 12.2 Receiving Notification of Documentation Updates
    3. 12.3 Support Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.5.5 Setting Input Current

System current normally fluctuates as portions of the system are powered up or put to sleep. With the input current limit, the output current requirement of the AC wall adapter can be lowered, reducing system cost.

The total input current, from a wall cube or other DC source, is the sum of the system supply current and the current required by the charger. When the input current exceeds the set input current limit, the BQ24725A decreases the charge current to provide priority to system load current. As the system current rises, the available charge current drops linearly to zero. Thereafter, all input current goes to system load and input current increases.

During DPM regulation, the total input current is the sum of the device supply current IBIAS, the charger input current, and the system load current ILOAD, and can be estimated as follows:

Equation 3. BQ24725A eq2_lusa79.gif

where η is the efficiency of the charger buck converter (typically 85% to 95%).

To set the input current limit, write a 16-bit InputCurrent() command (0x3FH or 0b00111111) using the data format listed in Table 6. When using a 10mΩ sense resistor, the BQ24725A provides an input-current limit range of 128mA to 8.064A, with 128mA resolution. The suggested input current limit is set to no less than 512mA. Sending InputCurrent() below 128mA or above 8.064A clears the register and terminates charging. Upon POR, the default input current limit is 4096mA.

The ACP and ACN pins are used to sense RAC with default value of 10mΩ. However, resistors of other values can also be used. For a larger sense resistor, larger sense voltage is given, and a higher regulation accuracy; but, at the expense of higher conduction loss.

If input current rises above FAST_DPM threshold, the charger will reduce charging current to allow the input current drop. After a typical 260-µs delay time, if input current is still above FAST_DPM threshold, the charger will shut down. The charger will soft restart to charge the battery if the adapter still has power to charge the battery. This prevents a crash if the adapter is overloaded when the system has a high and fast loading transient. The waiting time between shut down and restart charging is a natural response time of the input current limit loop.

Figure 17. Input Current Register (0x3FH), Using 10mΩ Sense Resistor
15 14 13 12 11 10 9 8
Not in use Not in use Not in use Input Current, DACIIN 5 Input Current, DACIIN 4 Input Current, DACIIN 3 Input Current, DACIIN 2 Input Current, DACIIN 1
R/W R/W R/W R/W R/W R/W R/W
7 6 5 4 3 2 1 0
Input Current, DACIIN 0 Not in use Not in use Not in use Not in use Not in use Not in use Not in use
R/W R/W R/W R/W R/W R/W R/W R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset

Table 6. Input Current Register (0x3FH), Using 10mΩ Sense Resistor

Bit Field Type Reset Description
[15] Not in use R/W Not used.
[14] Not in use R/W Not used.
[13] Not in use R/W Not used.
[12] Input Current, DACIIN 5 R/W 0 = Adds 0mA of input current.
1 = Adds 4096mA of input current.
[11] Input Current, DACIIN 4 R/W 0 = Adds 0mA of input current.
1 = Adds 2048mA of input current.
[10] Input Current, DACIIN 3 R/W 0 = Adds 0mA of input current.
1 = Adds 1024mA of input current.
[9] Input Current, DACIIN 2 R/W 0 = Adds 0mA of input current.
1 = Adds 512mA of input current.
[8] Input Current, DACIIN 1 R/W 0 = Adds 0mA of input current.
1 = Adds 256mA of input current.
[7] Input Current, DACIIN 0 R/W 0 = Adds 0mA of input current.
1 = Adds 128mA of input current.
[6] Not in use R/W Not used.
[5] Not in use R/w Not used.
[4] Not in use R/W Not used.
[3] Not in use R/W Not used.
[2] Not in use R/W Not used.
[1] Not in use R/W Not used.
[0] Not in use R/W Not used.