SLVS641B April   2008  – March  2015 TL4242

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 PWM Input
      2. 7.3.2 ST Output
        1. 7.3.2.1 Function and Timing Diagram
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Input Supply Voltage
      2. 8.1.2 Power Dissipation in TL4242
      3. 8.1.3 Setting the Output Current
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Input Voltage
        2. 8.2.2.2 Shunt Resistor
      3. 8.2.3 Application Curve
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Trademarks
    2. 11.2 Electrostatic Discharge Caution
    3. 11.3 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

パッケージ・オプション

メカニカル・データ（パッケージ｜ピン）
サーマルパッド・メカニカル・データ
発注情報

7 Detailed Description

7.1 Overview

The TL4242 device is an integrated, adjustable, constant-current source that can drive loads up to 500 mA. The output current level can be adjusted through an external resistor. The device is designed to supply high-power LEDs. Protection circuits prevent damage to the device in case of overload, short circuit, reverse polarity, and overtemperature. The connected LEDs are protected against reverse polarity as well as excess voltages up to 45 V. The integrated PWM input of the TL4242 permits LED brightness regulation by pulse-width modulation (PWM). Due to the high input impedance of the PWM input, the LED driver can be operated as a protected high-side switch.

7.2 Functional Block Diagram

TL4242 bd_lvs641.gif

7.3 Feature Description

7.3.1 PWM Input

The integrated PWM input of the TL4242 permits LED brightness regulation by pulse-width modulation (PWM). The overall LED brightness is a function of the shunt resistor, RREF, and the PWM duty cycle. The PWM input can also function as a simple enable control. When the PWM input is below VPWM,L, the device will go to a low-power consumption sleep mode. Due to the high input impedance of the PWM input, the LED driver can be operated as a protected high-side switch.

The LEDs are driven by a supply current that is adjusted by the resistor, RREF, preventing brightness variations due to forward voltage spread of the LEDs. The luminosity spread arising from the LED production process can be compensated through software by an appropriate duty cycle applied to the PWM pin. Therefore, it is not necessary to select LEDs for forward voltage or luminosity classes.

7.3.2 ST Output

The status output of the LED driver (ST) detects an open-load condition, enabling supervision of correct LED operation. An LED failure is detected as a voltage drop at the shunt resistor (RREF) below 25 mV (typical). In this case, the status output pin (ST) is set low after a delay time adjustable by an optional capacitor connected to pin D.

7.3.2.1 Function and Timing Diagram

The functionality and timing of ST and PWM are shown in Figure 5. The status delay can be adjusted through the capacitor connected to pin D. Delay time scales linearly with capacitance, CD:

Equation 1. TL4242 eq1_lvs641.gif
Equation 2. TL4242 eq2_lvs641.gif
TL4242 function_timing_lvs732.gifFigure 5. Function and Timing Diagram

7.4 Device Functional Modes

Table 1. Functional Modes

VPWM DEVICE MODE
High Active
Low Sleep