ZHCSGN9D February   2016  – March 2018 LM36274

PRODUCTION DATA.  

  1. 1 特性
  2. 2 应用
    1.     简化原理图
  3. 3 说明
    1.     背光效率，4P6S
  4. 4 修订历史记录
  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 I2C Timing Requirements (Fast Mode)
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Features Description
      1. 7.3.1 Enabling the LM36274
      2. 7.3.2 Backlight
        1. 7.3.2.1 Current Sink Enable
        2. 7.3.2.2 Brightness Mapping
          1. 7.3.2.2.1 Linear Mapping
          2. 7.3.2.2.2 Exponential Mapping
        3. 7.3.2.3 Backlight Brightness Control Modes
          1. 7.3.2.3.1 I2C Brightness Control (PWM Pin Disabled)
          2. 7.3.2.3.2 I2C × PWM Brightness Control (PWM Pin Enabled)
            1. 7.3.2.3.2.1 PWM Ramper
        4. 7.3.2.4 Boost Switching Frequency
          1. 7.3.2.4.1 Minimum Inductor Select
        5. 7.3.2.5 Boost Feedback Gain Select
        6. 7.3.2.6 Auto Switching Frequency
        7. 7.3.2.7 PWM Input
          1. 7.3.2.7.1 PWM Sample Frequency
            1. 7.3.2.7.1.1 PWM Resolution and Input Frequency Range
            2. 7.3.2.7.1.2 PWM Sample Rate and Efficiency
              1. 7.3.2.7.1.2.1 PWM Sample Rate Example
          2. 7.3.2.7.2 PWM Hysteresis
          3. 7.3.2.7.3 PWM Step Response
          4. 7.3.2.7.4 PWM Timeout
          5. 7.3.2.7.5 PWM-to-Digital Code Readback
        8. 7.3.2.8 Regulated Headroom Voltage
        9. 7.3.2.9 Backlight Fault Protection and Faults
          1. 7.3.2.9.1 Backlight Overvoltage Protection (OVP)
          2. 7.3.2.9.2 Backlight Overcurrent Protection (OCP)
      3. 7.3.3 LCM Bias
        1. 7.3.3.1 Display Bias Boost Converter (VVPOS, VVNEG)
        2. 7.3.3.2 Auto Sequence Mode
        3. 7.3.3.3 Wake-up Mode
          1. 7.3.3.3.1 Wake1 Mode
          2. 7.3.3.3.2 Wake2 Mode
        4. 7.3.3.4 Active Discharge
        5. 7.3.3.5 LCM Bias Protection and Faults
          1. 7.3.3.5.1 LCM Overvoltage (OVP) Protection
          2. 7.3.3.5.2 VPOS Short-Circuit Protection
          3. 7.3.3.5.3 VNEG Short-Circuit Protection
      4. 7.3.4 Software Reset
      5. 7.3.5 HWEN Input
      6. 7.3.6 Thermal Shutdown (TSD)
    4. 7.4 Device Functional Modes
      1. 7.4.1 Modes of Operation
    5. 7.5 Programming
      1. 7.5.1 I2C-Compatible Serial Bus Interface
        1. 7.5.1.1 Interface Bus Overview
        2. 7.5.1.2 Data Transactions
        3. 7.5.1.3 Acknowledge Cycle
        4. 7.5.1.4 Acknowledge After Every Byte Rule
        5. 7.5.1.5 Addressing Transfer Formats
        6. 7.5.1.6 Register Programming
    6. 7.6 Register Maps
      1. 7.6.1  Revision Register (Address = 0x01)[Reset = 0x01]
        1. Table 11. Revision Register Field Descriptions
      2. 7.6.2  Backlight Configuration1 Register (Address = 0x02)[Reset = 0x28]
        1. Table 12. Backlight Configuration 1 Register Field Descriptions
      3. 7.6.3  Backlight Configuration 2 Register (Address = 0x03)[Reset = 0x8D]
        1. Table 13. Backlight Configuration 2 Register Field Descriptions
      4. 7.6.4  Backlight Brightness LSB Register (Address = 0x04)[Reset = 0x07]
        1. Table 14. Backlight Brightness LSB Register Field Descriptions
      5. 7.6.5  Backlight Brightness MSB Register (Address = 0x05)[Reset = 0xFF]
        1. Table 15. Backlight Brightness MSB Register Field Descriptions
      6. 7.6.6  Backlight Auto-Frequency Low Threshold Register (Address = 0x06)[Reset = 0x00]
        1. Table 16. Backlight Auto-Frequency Low Threshold Field Descriptions
      7. 7.6.7  Backlight Auto-Frequency High Threshold Register (Address = 0x07)[Reset = 0x00]
        1. Table 17. Backlight Auto-Frequency High Threshold Field Descriptions
      8. 7.6.8  Backlight Enable Register (Address = 0x08)[Reset = 0x00]
        1. Table 18. Backlight Enable Register Field Descriptions
      9. 7.6.9  Bias Configuration 1 Register (Address = 0x09)[Reset = 0x18]
        1. Table 19. Bias Configuration 1 Register Field Descriptions
      10. 7.6.10 Bias Configuration 2 register (Address = 0x0A)[Reset = 0x11]
        1. Table 20. Bias Configuration 2 Register Field Descriptions
      11. 7.6.11 Bias Configuration 3 Register (Address = 0x0B)[Reset = 0x00]
        1. Table 21. Bias Configuration 3 Register Field Descriptions
      12. 7.6.12 LCM Boost Bias Register (Address = 0x0C)[Reset = 0x28]
        1. Table 22. LCM Boost Bias Register Field Descriptions
      13. 7.6.13 VPOS Bias Register (Address = 0x0D)[Reset = 0x1E]
        1. Table 23. VPOS Bias Register Field Descriptions
      14. 7.6.14 VNEG Bias Register (Address = 0x0E)[Reset = 0x1C]
        1. Table 24. VNEG Bias Register Field Descriptions
      15. 7.6.15 Flags Register (Address = 0x0F)[Reset = 0x00]
        1. Table 25. Flags Register Field Descriptions
      16. 7.6.16 Option 1 Register (Address = 0x10)[Reset = 0x06]
        1. Table 26. Option 1 Register Field Descriptions
      17. 7.6.17 Option 2 Register (Address = 0x11)[Reset = 0x35]
        1. Table 27. Option 2 Register Field Descriptions
      18. 7.6.18 PWM-to-Digital Code Readback LSB Register (Address = 0x12)[Reset = 0x00]
        1. Table 28. PWM-to-Digital Code Readback LSB Register Field Descriptions
      19. 7.6.19 PWM-to-Digital Code Readback MSB Register (Address = 0x13)[Reset = 0x00]
        1. Table 29. PWM-to-Digital Code Readback MSB Register Field Descriptions
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Component Selection
          1. 8.2.2.1.1 Inductor Selection
          2. 8.2.2.1.2 Boost Output Capacitor Selection
          3. 8.2.2.1.3 Input Capacitor Selection
      3. 8.2.3 Application Curves
        1. 8.2.3.1 Backlight Curves
          1. 8.2.3.1.1 Two LED Strings
          2. 8.2.3.1.2 Three LED Strings
          3. 8.2.3.1.3 Four LED Strings
        2. 8.2.3.2 LCM Bias Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11器件和文档支持
    1. 11.1 器件支持
      1. 11.1.1 第三方产品免责声明
      2. 11.1.2 开发支持
    2. 11.2 文档支持
      1. 11.2.1 相关文档
    3. 11.3 接收文档更新通知
    4. 11.4 社区资源
    5. 11.5 商标
    6. 11.6 静电放电警告
    7. 11.7 Glossary
  12. 12机械、封装和可订购信息

封装选项

机械数据 (封装 | 引脚)
散热焊盘机械数据 (封装 | 引脚)
订购信息

7.3.2.6 Auto Switching Frequency

To take advantage of frequency vs load dependent losses, the LM36274 can automatically change the boost switching frequency based on the programmed brightness code. In addition to the register programmable switching frequencies of 500 kHz and 1 MHz, the auto-frequency mode also incorporates a low-frequency selection of 250 kHz. It is important to note that the 250-kHz frequency is only accessible in auto-frequency mode and has a maximum boost duty cycle (DMAX) of 50%.

Auto-frequency mode operates by using two programmable registers (Backlight Auto Frequency Low Threshold (register 0x06) and Backlight Auto Frequency High Threshold (register 0x07)). The high threshold determines the switchover from 1 MHz to 500 kHz. The low threshold determines the switchover from 500 kHz to 250 kHz. Both the High and Low Threshold registers take an 8-bit code which is compared against the 8 MSB of the brightness register (register 0x05). Table 2 details the boundaries for this mode.

Table 2. Auto Switching Frequency Operation

BRIGHTNESS CODE MSBs (Register 0x05 bits[7:0]) BOOST SWITCHING FREQUENCY
< Auto Frequency Low Threshold (register 06 Bits[7:0]) 250 kHz (DMAX = 50%)
> Auto Frequency Low Threshold (Register 06 Bits[7:0]) and < Auto Frequency High Threshold (Register 07 Bits[7:0]) 500 kHz
≥ Auto Frequency High Threshold (register 07 Bits[7:0]) 1 MHz

Automatic-frequency mode is enabled whenever there is a non-zero code in either the Auto-Frequency High or Auto-Frequency Low registers. To disable the auto-frequency shift mode, set both registers to 0x00. When automatic-frequency select mode is disabled, the switching frequency operates at the programmed frequency (Register 0x03 bit[7]) across the entire LED current range. Table 3 provides a guideline for selecting the auto frequency threshold settings at VIN = 3.7 V. The actual setting must be verified in the application and optimized for the desired input voltage range.

Table 3. Auto Frequency Threshold Settings Examples, VIN = 3.7 V

CONDITION
(Vf = 3.35 V at ILED = 30 mA)		 INDUCTOR
(µH)		 RECOMMENDED AUTO FREQUENCY
HIGH THRESHOLD		 RECOMMENDED AUTO FREQUENCY
LOW THRESHOLD
2 × 4 LEDs 10 0x65 (12 mA) 0x43 (8 mA)
2 × 5 LEDs 10 0x5C (11 mA) 0x42 (7.9 mA)
2 × 6 LEDs 10 0x54 (10 mA) 0x3F (7.5 mA)
2 × 7 LEDs 10 0x4F (9.4 mA) 0x36 (6.5 mA)
2 × 8 LEDs 10 0x65 (12 mA) 0x3F (7.5 mA)
3 × 4 LEDs 10 0x4C (9 mA) 0x2A (5.1 mA)
3 × 5 LEDs 10 0x43 (8mA) 0x28 (4.8 mA)
3 × 6 LEDs 10 0x3B (7 mA) 0x27 (4.7 mA)
3 × 7 LEDs 10 0x35 (6.4 mA) 0x26 (4.6 mA)
3 × 8 LEDs 10 0x43 (8 mA) 0x25 (4.5 mA)
4 × 4 LEDs 10 0x5C (11 mA) 0x2B (5.2 mA)
4 × 5 LEDs 10 0x50 (9.5 mA) 0x28 (4.8 mA)
4 × 6 LEDs 10 0x50 (9.5 mA) 0x28 (4.8 mA)