SNOSCS2D November   2013  – March 2019 LM3697

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Boost Efficiency
  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 Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
      1. 7.1.1 PWM Input
      2. 7.1.2 HWEN Input
      3. 7.1.3 Thermal Shutdown
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Descriptions
      1. 7.3.1 High-Voltage LED Control
        1. 7.3.1.1 High-Voltage Boost Converter
        2. 7.3.1.2 High-Voltage Current Sinks (HVLED1, HVLED2 and HVLED3)
        3. 7.3.1.3 High-Voltage Current String Biasing
      2. 7.3.2 Boost Switching-Frequency Select
      3. 7.3.3 Automatic Switching Frequency Shift
      4. 7.3.4 Brightness Register Current Control
        1. 7.3.4.1 8-Bit Control (Preferred)
        2. 7.3.4.2 11-Bit Control
      5. 7.3.5 PWM Control
        1. 7.3.5.1 PWM Input Frequency Range
        2. 7.3.5.2 PWM Input Polarity
        3. 7.3.5.3 PWM Zero Detection
      6. 7.3.6 Start-up/Shutdown Ramp
      7. 7.3.7 Run-Time Ramp
      8. 7.3.8 High-Voltage Control A and B Ramp Select
    4. 7.4 Device Functional Modes
      1. 7.4.1 LED Current Mapping Modes
        1. 7.4.1.1 Exponential Mapping
          1. 7.4.1.1.1 8-Bit Code Calculation
          2. 7.4.1.1.2 11-Bit Code Calculation
        2. 7.4.1.2 Linear Mapping
          1. 7.4.1.2.1 8-Bit Code Calculation
          2. 7.4.1.2.2 11-Bit Code Calculation
      2. 7.4.2 Fault Flags/Protection Features
        1. 7.4.2.1 Open LED String (HVLED)
        2. 7.4.2.2 Shorted LED String (HVLED)
        3. 7.4.2.3 Overvoltage Protection (Inductive Boost)
        4. 7.4.2.4 Current Limit (Inductive Boost)
      3. 7.4.3 I2C-Compatible Interface
        1. 7.4.3.1 Start And Stop Conditions
        2. 7.4.3.2 I2C-Compatible Address
        3. 7.4.3.3 Transferring Data
        4. 7.4.3.4 High-Speed Mode
    5. 7.5 Register Maps
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Boost Converter Maximum Output Power
          1. 8.2.2.1.1 Peak Current Limited
          2. 8.2.2.1.2 Output Voltage Limited
        2. 8.2.2.2 Inductor Selection
        3. 8.2.2.3 Output Capacitor Selection
        4. 8.2.2.4 Schottky Diode Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Application Circuit Component List
      3. 8.2.3 Application Performance Plots
    3. 8.3 Initialization Set Up
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Boost Output Capacitor Placement
      2. 10.1.2 Schottky Diode Placement
      3. 10.1.3 Inductor Placement
      4. 10.1.4 Boost Input Capacitor Placement
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.3 Initialization Set Up

Table 25 illustrates the minimum number of register writes required for a two-parallel, seven-series LED configuration. This example uses the default settings for ramp times (2048 µsec), mapping mode (exponential) and full-scale current (20.2 mA). In this mode of operation the LM3697 controls the brightness LSB's to ramp between the 8-bit MSB brightness levels providing 11-bit dimming while requiring only 8-bit commands from the host controller.

Table 25. Control Bank A, 8-Bit Control, Two-String, Seven Series LED Configuration Example

REGISTER NAME ADDRESS DATA DESCRIPTION
HVLED Current Sink Output Configuration 0x10 0x04 HVLED1 & 2 assigned to Control Bank A
HVLED Current Sink Feedback Enables 0x19 0x03 Enable feedback on HVLED1 & 2, disable feedback on HVLED3
Boost Control 0x1A 0x04 OVP = 32V, ƒsw = 500 kHz
Control Bank Enables 0x24 0x01 Enable Control Bank A
Control A Brightness LSB 0x20 0x00 Control A Brightness LSB written only once
Control A Brightness MSB 0x21 User Value Control A Brightness MSB updated as required

Table 26 shows the minimum number of register writes required for a two-parallel, six-series LED configuration with PWM Enabled. This example uses the default settings for ramp times (2048 µsec), mapping mode (exponential) and full-scale current (20.2 mA). In this mode of operation the host controller must update both the brightness LSB and MSB registers whenever a brightness change is required.

Table 26. Control Bank A, 11-Bit Control, Two-String, Six Series LED Configuration Example

REGISTER NAME ADDRESS DATA DESCRIPTION
HVLED Current Sink Output Configuration 0x10 0x04 HVLED1 & 2 assigned to Control Bank A
HVLED Current Sink Feedback Enables 0x19 0x03 Enable feedback on HVLED1 & 2, disable feedback on HVLED3
Boost Control 0x1A 0x02 OVP = 24 V, ƒsw = 500 kHz
PWM Configuration 0x1C 0x0D PWM Zero Detect = Enabled, PWM Polarity = Active HIgh, Control B PWM = Disabled, Control A PWM = Enabled
Control Bank Enables 0x24 0x01 Enable Control Bank A
Control A Brightness LSB 0x20 User Value Control A Brightness LSB updated as required
(NOTE: The Brightness LSB change does not take effect until the Brightness MSB register is written.)
Control A Brightness MSB 0x21 User Value Control A Brightness MSB updated as required
(NOTE: Anytime the Brightness LSB is changed the Brightness MSB must be written for the Brightness LSB change to take effect.)