SNVSA40A October   2014  – March 2016 TPS61169

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Simplified Schematic
  5. 5 Revision History
  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 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Soft Start-Up
      2. 8.3.2 Open LED Protection
      3. 8.3.3 Shutdown
      4. 8.3.4 Current Program
      5. 8.3.5 LED Brightness Dimming
      6. 8.3.6 Undervoltage Lockout
      7. 8.3.7 Thermal Foldback and Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Operation With CTRL
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Inductor Selection
        2. 9.2.2.2 Schottky Diode Selection
        3. 9.2.2.3 Output Capacitor Selection
        4. 9.2.2.4 LED Current Set Resistor
        5. 9.2.2.5 Thermal Considerations
    3. 9.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

9 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.

9.1 Application Information

The TPS61169 device is a step-up DC-DC converter which can drive single or parallel LED strings for small- to large-size panel backlighting. This section includes a design procedure (Detailed Design Procedure) to select component values for the TPS61169 typical application (Figure 4).

9.2 Typical Application

TPS61169 typ_app_snvsa40.gif Figure 4. TPS61169 2.7-V to 5.5-V Input, 10 LEDs in Series Output Converter

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 1 as the input parameters.

Table 1. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Input voltage range 2.7 V to 5.5 V
Output, LED number in a string 10
Output, LED string number 1
Output, LED current per string 20 mA

9.2.2 Detailed Design Procedure

9.2.2.1 Inductor Selection

The selection of the inductor affects power efficiency, steady state operation as well as transient behavior and loop stability. These factors make it the most important component in power regulator design. There are three important inductor specifications, inductor value, DC resistance and saturation current. Considering inductor value alone is not enough. The inductor value determines the inductor ripple current. Choose an inductor that can handle the necessary peak current without saturating. Follow Equation 3 to Equation 4 to calculate the peak current of the inductor. To calculate the current in the worst case, use the minimum input voltage, maximum output voltage and maximum load current of application. In a boost regulator, the input DC current can be calculated as Equation 3.

Equation 3. TPS61169 eq003_snvsa40.gif

where

  • VOUT = boost output voltage
  • IOUT = boost output current
  • VIN = boost input voltage
  • η = power conversion efficiency

The inductor current peak to peak ripple can be calculated as Equation 4.

Equation 4. TPS61169 eq004_snvsa40.gif

where

  • ΔIL(PP) = inductor peak-to-peak ripple
  • L = inductor value
  • FS = boost switching frequency
  • VOUT = boost output voltage
  • VIN = boost input voltage

Therefore, the peak current IL(P) seen by the inductor is calculated with Equation 5.

Equation 5. TPS61169 eq005_snvsa40.gif

Inductor values can have ±20% tolerance with no current bias. When the inductor current approaches saturation level, its inductance can decrease 20% to 35% from the 0-A value depending on how the inductor vendor defines saturation current. Using an inductor with a smaller inductance value forces discontinuous PWM when the inductor current ramps down to zero before the end of each switching cycle. This reduces the boost converter’s maximum output current, causes large input voltage ripple and reduces efficiency. Large inductance value provides much more output current and higher conversion efficiency. For these reasons, a 4.7-μH to 10-μH inductor value range is recommended, and 4.7-μH inductor is recommended for higher than 5-V input voltage by considering inductor peak current and loop stability. Table 2 lists the recommended inductor for the TPS61169.

Table 2. Recommended Inductors for TPS61169

PART NUMBER L (µH) DCR MAX (mΩ) SATURATION CURRENT (A) SIZE (L x W x H mm) VENDOR
LPS4018-472ML 4.7 125 1.9 4 × 4 × 1.8 Coilcraft
LPS4018-103ML 10 200 1.3 4 × 4 × 1.8 Coilcraft
PCMB051H-4R7M 4.7 85 4 5.4 × 5.2 × 1.8 Cyntec
PCMB051H-100M 10 155 3 5.4 × 5.2 × 1.8 Cyntec

9.2.2.2 Schottky Diode Selection

The TPS61169 demands a low forward voltage, high-speed and low capacitance Schottky diode for optimum efficiency. Ensure that the diode average and peak current rating exceeds the average output current and peak inductor current. In addition, the diode reverse breakdown voltage must exceed the open LED protection voltage. ONSemi NSR0240 is recommended for the TPS61169.

9.2.2.3 Output Capacitor Selection

The output capacitor is mainly selected to meet the requirement for the output ripple and loop stability. This ripple voltage is related to capacitor capacitance and its equivalent series resistance (ESR). Assuming a capacitor with zero ESR, the minimum capacitance needed for a given ripple can be calculated with Equation 6:

Equation 6. TPS61169 eq006_snvsa40.gif

where

  • Vripple = peak-to-peak output ripple

The additional part of the ripple caused by ESR is calculated using: Vripple_ESR = IOUT × RESR

Due to its low ESR, Vripple_ESR could be neglected for ceramic capacitors, a 1-µF to 4.7-µF capacitor is recommended for typical application.

9.2.2.4 LED Current Set Resistor

The LED current set resistor can be calculated by Equation 1.

9.2.2.5 Thermal Considerations

The allowable IC junction temperature must be considered under normal operating conditions. This restriction limits the power dissipation of the TPS61169. The allowable power dissipation for the device can be determined by Equation 7:

Equation 7. TPS61169 eq08_snvsa40.gif

where

  • TJ is allowable junction temperature given in recommended operating conditions
  • TA is the ambient temperature for the application
  • RθJA is the thermal resistance junction-to-ambient given in Power Dissipation Table

The TPS61169 device also features a thermal foldback function to reduce the thermal stress automatically.

9.3 Application Curves

Typical application condition is as in Figure 4, VIN = 3.6 V, RSET = 10.2 Ω, L = 4.7 µH, COUT = 1 µF, 10 LEDs in series (unless otherwise specified).
TPS61169 D003_SNVSA40.gif
Figure 5. Efficiency vs Dimming Duty Cycle
TPS61169 D005_SNVSA40.gif
8 LEDs in series
Figure 7. Efficiency vs Dimming Duty Cycle
TPS61169 wvfm01_switch_dim_duty_100p_snvsa40.gif
Time = 1 µs/DIV
Figure 9. Switching-Dimming Duty = 100%
TPS61169 wvfm03_switch_dim_duty_10p_snvsa40.gif
Time = 2 µs/DIV
Figure 11. Switching-Dimming Duty = 10%
TPS61169 wvfm05_startup_dim_duty_50p_snvsa40.gif
Time = 2 ms/DIV
Figure 13. Start-Up Dimming Duty = 50%
TPS61169 wvfm07_shutdown_dim_duty_50p_snvsa40.gif
Time = 2 ms/DIV
Duty = 50%
Figure 15. Shutdown Dimming
TPS61169 wvfm09_open_protection_snvsa40.gif
Time = 50 µs/DIV
Figure 17. Open LED Protection
TPS61169 D004_SNVSA40.gif
10 LEDs in series
Figure 6. Efficiency vs Dimming Duty Cycle
TPS61169 D006_SNVSA40.gif
6 LEDs in series
Figure 8. Efficiency vs Dimming Duty Cycle
TPS61169 wvfm02_switch_dim_duty_50p_snvsa40.gif
Time = 1 µs/DIV
Figure 10. Switching-Dimming Duty = 50%
TPS61169 wvfm04_startup_dim_duty_100p_snvsa40.gif
Time = 2 ms/DIV
Figure 12. Start-Up Dimming Duty = 100%
TPS61169 wvfm06_shutdown_dim_duty_100p_snvsa40.gif
Time = 2 ms/DIV
Figure 14. Shutdown Dimming Duty = 100%
TPS61169 wvfm08_transient_dim_snvsa40.gif
Time = 5 ms/DIV
Duty = 1%-100%-1%
Figure 16. Dimming Transient-Dimming