SLVS814A January   2008  – May 2015 TLC5916-Q1 , TLC5917-Q1

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  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: VDD = 3 V
    6. 7.6  Electrical Characteristics: VDD = 5.5 V
    7. 7.7  Timing Requirements
    8. 7.8  Switching Characteristics: VDD = 3 V
    9. 7.9  Switching Characteristics: VDD = 5.5 V
    10. 7.10 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 Open-Circuit Detection Principle
      2. 9.3.2 Short-Circuit Detection Principle (TLC5917-Q1 Only)
      3. 9.3.3 Overtemperature Detection and Shutdown
    4. 9.4 Device Functional Modes
      1. 9.4.1 Operation Mode Switching
        1. 9.4.1.1 Normal Mode Phase
        2. 9.4.1.2 Special Mode Phase
    5. 9.5 Programming
      1. 9.5.1 Reading Error Status Code in Special Mode
      2. 9.5.2 Writing Configuration Code in Special Mode
      3. 9.5.3 8-Bit Configuration Code and Current Gain
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Constant Current
      2. 10.1.2 Adjusting Output Current
    2. 10.2 Typical Applications
      1. 10.2.1 Single Implementation of TLC591x-Q1 Device
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedure
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Cascading Implementation of TLC591x-Q1 Device
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Links
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

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 Constant Current

In LED display applications, the TLC591x-Q1 provides nearly no current variations from channel to channel and from IC to IC. While IOUT ≤ 100 mA, the maximum current skew between channels is less than ±3% and between ICs is less than ±6%.

10.1.2 Adjusting Output Current

The TLC591x-Q1 scales up the reference current, Iref, set by the external resistor Rext to sink a current, Iout, at each output port. Use the following formulas to calculate the target output current

Equation 1. IOUT,target in the saturation region:
Equation 2. Iref = VR-EXT/Rext, if another end of the external resistor Rext is connected to groundVR-EXT = 1.26 V × VG
Equation 3. IOUT,target = Iref × 15 × 3CM – 1

where

  • Rext is the resistance of the external resistor connected to the R-EXT terminal.
  • VR-EXT is the voltage of R-EXT, which is controlled by the programmable voltage gain (VG), which is defined by the Configuration Code.

The Current Multiplier (CM) determines that the ratio IOUT,target/Iref is 15 or 5. After power on, the default value of VG is 127/128 = 0.992, and the default value of CM is 1, so that the ratio IOUT,target/Iref = 15. Based on the default VG and CM.

Equation 4. VR-EXT = 1.26 V × 127/128 = 1.25 V
Equation 5. IOUT,target = (1.25 V/Rext) × 15

Therefore, the default current is approximately 52 mA at 360 Ω and 26 mA at 720 Ω. The default relationship after power on between IOUT,target and Rext is shown in Figure 19.

TLC5916-Q1 TLC5917-Q1 g_iout_rext_lvs814.gifFigure 19. Default Relationship Curve Between IOUT,target and Rext After Power Up

10.2 Typical Applications

10.2.1 Single Implementation of TLC591x-Q1 Device

The TLC5917/TLC5917-Q1 Constant-Current LED Sink Drivers is designed to work alone or cascaded. Figure 20 shows implementation of a single TLC591x-Q1 device.

TLC5916-Q1 TLC5917-Q1 single_implementation_TLC5916_TLC5917_Q1_slvs814.gifFigure 20. Single Implementation of TLC591x-Q1 Device

10.2.1.1 Design Requirements

For this design example, use the parameters listed in Table 6. The purpose of this design procedure is to calculate the power dissipation in the device and the operating junction temperature.

Table 6. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Number of LED strings 8
Number of LEDs per string 3
LED Current (mA) 20
Forward voltage of each LED (V) 3.5
Junction-to-ambient thermal resistance (°C/W) 86.9
Ambient temperature of application (°C) 115
VDD (V) 5
IDD (mA) 10
Max operating junction temperature (°C) 150

10.2.1.2 Detailed Design Procedure

Use the following equations to determine the design parameters.

Equation 6. TJ = TA + RθJA × PD_TOT

where

  • TJ is the junction temperature
  • TA is the ambient temperature
  • RθJA is the junction-to-ambient thermal resistance
  • PD_TOT is the total power dissipation in the IC.
Equation 7. PD_TOT = PD_CS + IDD × VDD

where

  • PD_CS is the power dissipation in the LED current sinks.
  • IDD is the IC supply current.
  • VDD is the IC supply voltage.
Equation 8. PD_CS = IO × VO × nCH

where

  • IO is the LED current
  • VO is the voltage at the output pin
  • nCH is the number of LED strings.
Equation 9. VO = VLED – (nLED × VF)

where

  • VLED is the voltage applied to the LED string
  • nLED is the number of LEDs in the string
  • VF is the forward voltage of each LED.

VO must not be too high as this causes excess power dissipation inside the current sink. However, VO also must not be too low as this does not allow the full LED current Figure 21.

With VLED = 12 V:

Equation 10. VO = 12 V – (3 × 3.5 V) = 1.5 V
Equation 11. PD_CS = 20 mA × 1.5 V × 8 = 0.24 W

Using PD_CS, calculate:

Equation 12. PD_TOT = PD_CS + IDD × VDD = 0.24 W + 0.01 A × 5 V = 0.29 W

Using PD_TOT, calculate:

Equation 13. TJ = TA + RθJA × PD_TOT = 115°C + 86.9°C/W × 0.29 W = 140°C

This design example demonstrates how to calculate power dissipation in the IC and ensure that the junction temperature is kept below 150°C.

NOTE

This design example assumes that all channels have the same electrical parameters (nLED, IO, VF, VLED). If the parameters are unique for each channel, then the power dissipation must be calculated for each current sink separately. Then, add each result together to calculate the total power dissipation in the current sinks.

10.2.1.3 Application Curve

TLC5916-Q1 TLC5917-Q1 g_iout_vout_lvs695.gifFigure 21. Output Current vs Output Voltage

10.2.2 Cascading Implementation of TLC591x-Q1 Device

The TLC5917/TLC5917-Q1 Constant-Current LED Sink Drivers is designed to work alone or cascaded. Figure 22 shows a cascaded driver implementation.

TLC5916-Q1 TLC5917-Q1 cascading_implementation_of_TLC5916_TLC5917_q1_slvs814.gifFigure 22. Cascading Implementation of TLC591x-Q1 Device