SCLS715A March   2009  – November 2015 TLC59208F

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 I2C Interface Timing Requirements
    7. 7.7 Typical Characteristics
  8. 8 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Power-On Reset
      2. 9.3.2 External Reset
      3. 9.3.3 Software Reset
      4. 9.3.4 Individual Brightness Control With Group Dimming/Blinking
    4. 9.4 Device Functional Modes
    5. 9.5 Programming
      1. 9.5.1 Characteristics of the I2C Bus
        1. 9.5.1.1 Bit Transfer
        2. 9.5.1.2 Start and Stop Conditions
      2. 9.5.2 System Configuration
      3. 9.5.3 Acknowledge
      4. 9.5.4 Device Address
      5. 9.5.5 Regular I2C Bus Slave Address
        1. 9.5.5.1 Regular I2C Bus Slave Address
      6. 9.5.6 LED All Call I2C Bus Address
      7. 9.5.7 LED Sub Call I2C Bus Address
      8. 9.5.8 Software Reset I2C Bus Address
      9. 9.5.9 Control Register
    6. 9.6 Register Maps
      1. 9.6.1 Register Descriptions
        1. 9.6.1.1 Mode Register 1 (MODE1)
        2. 9.6.1.2 Mode Register 2 (MODE2)
        3. 9.6.1.3 Individual Brightness Control Registers (PWM0-PWM7)
        4. 9.6.1.4 Group Duty Cycle Control Register (GRPPWM)
        5. 9.6.1.5 Group Frequency Register (GRPFREQ)
        6. 9.6.1.6 LED Driver Output State Registers (LEDOUT0, LEDOUT1)
        7. 9.6.1.7 I2C Bus Sub-Address Registers 1 to 3 (SUBADR1-SUBADR3)
        8. 9.6.1.8 LED All Call I2C Bus Address Register (ALLCALLADR)
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Setting LED Current
      2. 10.1.2 PWM Brightness Dimming
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
      3. 10.2.3 Application Curve
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Trademarks
    2. 13.2 Community Resources
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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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

10.1.1 Setting LED Current

The LED current is primarily dependent on the supply voltage, the forward voltage of the LED, and the series resistor (RSET). In many applications the supply voltage and LED forward voltage cannot be adjusted. Hence, RSET is utilized to adjust the LED current. This calculation is discussed in detail in the typical application example.

10.1.2 PWM Brightness Dimming

The perceived brightness of the LEDs can be adjusted by use of PWM dimming. For example, an LED driven at 50% duty cycle will appear less bright than it would at 100% duty cycle. The TLC59208F offers duty cycle control for each individual channel and also offers group duty cycle control. Refer to the Register Map for details regarding programmable duty cycle.

10.2 Typical Application

This application example provides guidance on how to set the LED current using the TLC59208F.

TLC59208F app_drawing_scls715.gif Figure 20. Typical Application

10.2.1 Design Requirements

For this design example, use Table 12 the following as the input parameters.

Table 12. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
VLED Supply voltage that powers the LED 5-V
VF Forward voltage across the LED 3-V
ILED Current flowing through the LED 6-mA
RON Resistance across open-drain output 1.5-Ω

10.2.2 Detailed Design Procedure

In the LED current path, there are three voltage drops that must be considered:

  • Drop across the series resistor (VRSET)
  • Drop across the LED (VF)
  • Drop across the open-drain output channel (VO)

The drop across the LED is defined above as VF = 3 V. The drop across the open-drain output is calculated as RON × ILED (1.5 × 0.006 = 0.009 V). The remaining voltage must be across the series resistor:

Equation 1. 5 V = 3 V + 0.009 V + VRSET
Equation 2. VRSET = 1.991 V

After calculating VRSET, we can calculate RSET:

Equation 3. VRSET = ILED × RSET
Equation 4. 1.991 V = 0.006 mA × RSET
Equation 5. RSET = 332 Ω

10.2.3 Application Curve

The following graph shows the typical LED Current as a function of RSET and VF. The graph assumes that VLED = 5 V.

TLC59208F C001_SLDS162.png Figure 21. LED Current vs RSET