ZHCS036C February   2011  – April 2015 BQ24171

PRODUCTION DATA.  

  1. 特性
  2. 应用
  3. 说明
  4. 修订历史记录
  5. 说明(续)
  6. Device Comparison Table
  7. Pin Configuration and Functions
  8. Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Typical Characteristics
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1  Battery Voltage Regulation
      2. 9.3.2  Battery Current Regulation
      3. 9.3.3  Battery Precharge Current Regulation
      4. 9.3.4  Input Current Regulation
      5. 9.3.5  Charge Termination, Recharge, and Safety Timers
      6. 9.3.6  Power Up
      7. 9.3.7  Input Undervoltage Lockout (UVLO)
      8. 9.3.8  Input Overvoltage/Undervoltage Protection
      9. 9.3.9  Enable and Disable Charging
      10. 9.3.10 System Power Selector
      11. 9.3.11 Converter Operation
      12. 9.3.12 Automatic Internal Soft-Start Charger Current
      13. 9.3.13 Charge Overcurrent Protection
      14. 9.3.14 Charge Undercurrent Protection
      15. 9.3.15 Battery Detection
        1. 9.3.15.1 Example
      16. 9.3.16 Battery Short Protection
      17. 9.3.17 Battery Overvoltage Protection
      18. 9.3.18 Temperature Qualification and JEITA Guideline
      19. 9.3.19 MOSFET Short Circuit and Inductor Short Circuit Protection
      20. 9.3.20 Thermal Regulation and Shutdown Protection
      21. 9.3.21 Timer Fault Recovery
      22. 9.3.22 Inductor, Capacitor, and Sense Resistor Selection Guidelines
      23. 9.3.23 Charge Status Outputs
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Inductor Selection
        2. 10.2.2.2 Input Capacitor
        3. 10.2.2.3 Output Capacitor
        4. 10.2.2.4 Input Filter Design
        5. 10.2.2.5 Input ACFET and RBFET Selection
      3. 10.2.3 Application Curves
    3. 10.3 System Examples
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13器件和文档支持
    1. 13.1 器件支持
    2. 13.2 文档支持
      1. 13.2.1 相关文档
    3. 13.3 商标
    4. 13.4 静电放电警告
    5. 13.5 术语表
  14. 14机械、封装和可订购信息

10 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

10.1 Application Information

A typical application consists of a bq24171 with power path management and from 1- to 3-cell series Li-ion or Li-polymer battery in a wide variety of portable applications where JEITA-compatible charging limits are desired.

10.2 Typical Application

bq24171 typ_app1_lusaf2.gif
12-V input, 2-cell battery 8.4 V, 2-A charge current, 0.2-A precharge/termination current, 3-A DPM current, 18-V input OVP
Figure 19. Typical Application Schematic

10.2.1 Design Requirements

For this design example, use the parameters listed in Table 4 as the input parameters.

Table 4. Design Parameters

PARAMETER EXAMPLE VALUE
Input Voltage Range 4.5 V - 17 V
Input Current DPM Limit 600 mA min
Battery Voltage 13.5 V max
Charge Current 4 A max

10.2.2 Detailed Design Procedure

10.2.2.1 Inductor Selection

The bq24171 has a 1600-kHz switching frequency to allow the use of small inductor and capacitor values. Inductor saturation current should be higher than the charging current (ICHG) plus half the ripple current (IRIPPLE):

Equation 12. bq24171 EQ11_Isat_lusa75.gif

Inductor ripple current depends on input voltage (VIN), duty cycle (D = VOUT/VIN), switching frequency (fs), and inductance (L):

Equation 13. bq24171 EQ12_IRIPPLE_lusa75.gif

The maximum inductor ripple current happens with D = 0.5 or close to 0.5. Usually inductor ripple is designed in the range of 20% to 40% of the maximum charging current as a trade-off between inductor size and efficiency for a practical design.

10.2.2.2 Input Capacitor

The input capacitor should have enough ripple current rating to absorb input switching ripple current. The worst case RMS ripple current is half of the charging current when duty cycle is 0.5. If the converter does not operate at 50% duty cycle, then the worst case capacitor RMS current ICIN occurs where the duty cycle is closest to 50% and can be estimated by the following equation:

Equation 14. bq24171 EQ13_ICIN_lusa75.gif

A low ESR ceramic capacitor such as X7R or X5R is preferred for the input decoupling capacitor and should be placed as close as possible to the drain of the high-side MOSFET and source of the low-side MOSFET. The voltage rating of the capacitor must be higher than the normal input voltage level. A 25-V rating or higher capacitor is preferred for a 15-V input voltage. A 20-μF capacitance is suggested for a typical 3-A to 4-A charging current.

10.2.2.3 Output Capacitor

The output capacitor also should have enough ripple current rating to absorb output switching ripple current. The output capacitor RMS current ICOUT is given as:

Equation 15. bq24171 EQ14_ICOUT_lusa75.gif

The output capacitor voltage ripple can be calculated as follows:

Equation 16. bq24171 EQ15_DVO_lusa75.gif

At certain input/output voltages and switching frequencies, the voltage ripple can be reduced by increasing the output filter LC.

The bq24171 has an internal loop compensator. To achieve good loop stability, the resonant frequency of the output inductor and output capacitor should be designed from 15 kHz to 25 kHz. The preferred ceramic capacitor has a 25-V or higher rating, X7R or X5R.

10.2.2.4 Input Filter Design

During adapter hot plug-in, the parasitic inductance and the input capacitor from the adapter cable form a second-order system. The voltage spike at the AVCC pin may be beyond the IC maximum voltage rating and damage the IC. The input filter must be carefully designed and tested to prevent an overvoltage event on the AVCC pin.

There are several methods to damping or limiting the overvoltage spike during adapter hot plug-in. An electrolytic capacitor with high ESR as an input capacitor can damp the overvoltage spike well below the IC maximum pin voltage rating. A high current capability TVS Zener diode can also limit the overvoltage level to an IC safe level. However, these two solutions may not be lowest cost or smallest size.

A cost-effective and small-size solution is shown in Figure 20. R1 and C1 are composed of a damping RC network to damp the hot plug-in oscillation. As a result, the overvoltage spike is limited to a safe level. D1 is used for reverse voltage protection for the AVCC pin. C2 is the AVCC pin decoupling capacitor and it should be placed as close as possible to the AVCC pin. R2 and C2 form a damping RC network to further protect the IC from high dv/dt and high voltage spikes. The C2 value should be less than the C1 value so R1 can dominant the equivalent ESR value to provide enough damping effect for hot plug-in. R1 and R2 must be sized to handle in-rush current power loss according to the resistor manufacturer’s data sheet. Verify the filter component values with a real application and make any minor adjustments needed to fit in the real application circuit.

If the input is 5 V (USB host or USB adapter), diode D1 can be omitted. R2 must be 5 Ω or higher to limit the current if the input is reversely inserted.

bq24171 input_flt_lusad2.gif Figure 20. Input Filter

10.2.2.5 Input ACFET and RBFET Selection

N-type MOSFETs are used as input ACFET(Q1) and RBFET(Q2) for better cost-effective and small-size solution, as shown in Figure 23. Normally, there is a total capacitance of 50 µF connected at PVCC node; 10-µF capacitor for buck converter of bq24171 and 40-µF capacitor for system side. There is a surge current during Q1 turnon period when a valid adapter is inserted. Decreasing the turnon speed of Q1 can limit this surge current in desirable range by selecting a MOSFET with relative bigger CGD and/or CGS. If Q1 turns on too fast, we must add external CGD and/or CGS. For example, 4.7-nF CGD and 47-nF CGS are adopted on EVM while using NexFET CSD17313 as Q1.

bq24171 In_ACFET_RBFET_lusaf2.gif Figure 21. Input ACFET and RBFET

10.2.3 Application Curves

bq24171 D001_SLUSAF7.gif Figure 22. Charge Efficiency

10.3 System Examples

bq24171 typ_app2_lusaf2.gif
USB with input OVP 8 V, selectable charge current limit of 900 mA or 500 mA, system connected after sense resistor
Figure 23. Typical Application Schematic With Single-Cell Unremovable Battery