SLVS465C December   2003  – February 2016 TPS61043

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 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Operation
      2. 8.3.2 Boost Converter
      3. 8.3.3 Peak Current Control (Boost Converter)
      4. 8.3.4 Softstart
      5. 8.3.5 Control (CTRL)
    4. 8.4 Device Functional Modes
      1. 8.4.1 Overvoltage Protection (OVP)
      2. 8.4.2 Undervoltage Lockout
      3. 8.4.3 Thermal Shutdown
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 Efficiency
      2. 9.1.2 Setting the LED Current
      3. 9.1.3 Analog Control Signal for Brightness Control
      4. 9.1.4 PWM Control With Separate Enable
    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, Maximum Load Current, and Switching Frequency
        2. 9.2.2.2 Output Capacitor Selection and Line Regulation
        3. 9.2.2.3 Input Capacitor Selection
        4. 9.2.2.4 Diode Selection
      3. 9.2.3 Application Curves
    3. 9.3 System Examples
      1. 9.3.1 TPS61043 With 1-mm Total System Height
      2. 9.3.2 TPS61043 With Low LED Ripple Current and Higher Accuracy Using a 4.7-µF Output Capacitor
      3. 9.3.3 TPS61043 Powering 3 LEDs
      4. 9.3.4 Adjustable Brightness Control Using an Analog Voltage
      5. 9.3.5 Alternative Adjustable Brightness Control Using PWM Signal
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Documentation
    3. 12.3 Community Resources
    4. 12.4 Trademarks
    5. 12.5 Electrostatic Discharge Caution
    6. 12.6 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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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

Table 2. Possible Diodes (or Equivalent)

COMPONENT SUPPLIER REVERSE VOLTAGE
ON Semiconductor MBR0530 30 V
ON Semiconductor MBR0520 20 V
Toshiba CRS02 30 V
Zetex ZHCS400 40 V

9.1.1 Efficiency

The overall efficiency of the application depends on the specific application conditions and mainly on the selection of the inductor. A lower inductor value increases the switching frequency and switching losses yielding in a lower efficiency. A lower inductor dc resistance has lower copper losses, giving a higher efficiency. Therefore, the efficiency can typically vary ±5% depending on the selected inductor. and can be used as a guideline for the application efficiency. These curves show the typical efficiency powering four LEDs using a 4.7-µH inductor with just 1,2 mm height. The efficiency curve in and show the efficiency delivering the power to the LEDs rather than the overall converter efficiency and is calculated as:

Equation 3. TPS61043 Q_Effiec_lvs441.gif

9.1.2 Setting the LED Current

The converter regulates the LED current by regulating the voltage across the current sense resistor (RS). The voltage across the sense resistor is regulated to the internal reference voltage of V(FB) = 252 mV.

TPS61043 set_led_cur1_lvs465.gif Figure 10. Setting the LED Current

The LED current can be calculated:

Equation 4. TPS61043 Q_LEDCur_lvs441.gif

The current programming method is used when the brightness of the LEDs is fixed or controlled by a PWM signal applied to the CTRL pin. When using a PWM signal on the CTRL pin, the LED brightness is only dependent on the PWM duty cycle, independent of the PWM frequency, or amplitude, which simplifies the system.

9.1.3 Analog Control Signal for Brightness Control

Alternatively, an analog voltage can be used as well to control the LED brightness.

TPS61043 set_led_cur2_lvs465.gif Figure 11. Setting the LED Current Using an Analog Control Signal

In Figure 11 the LED current is determined by the voltage applied to R2 (VADJ) and the selection of R1, R2 and the sense resistor (RS). In this configuration, the LED current is linear controlled instead of pulsed as in the configuration before. To select the resistor values following steps are required.

  1. Select the voltage VADJ(max) to turn the LEDs off, for example, 3.3 V
  2. Select the voltage VADJ(min) to turn the LEDs fully on, for example, 0 V
  3. Select the maximum and minimum LED current IO(max) and IO(min), for example, IO(max) = 20 mA, IO(min) = 0 mA
  4. Calculate R2 to achieve a feedback current in the range of I1 = 3 µA to 10 µA as the LEDs are fully turned on:
    5. Equation 5. TPS61043 q_r2fdbkcur_lvs465.gif
  5. Calculate R1
    6. Equation 6. TPS61043 q_r1_lvs465.gif
  6. Calculate the sense voltage (VS) at maximum LED current
    7. Equation 7. TPS61043 q_sensevlt_lvs465.gif
  7. Calculate the required sense resistor (RS)
    8. Equation 8. TPS61043 Q_ReqSnsRes_lvs441.gif

9.1.4 PWM Control With Separate Enable

The control pin (CTRL) combines the enable function as well as the PWM brightness control function in one pin. For some systems an independent enable function is required. One way to implement this is to use the brightness control configuration as shown in the previous section Figure 11.

Other possible solutions are shown in Figure 12, Figure 13, Figure 14.

TPS61043 schottky_lvs465.gif Figure 12. Separate Enable and PWM Control Using a Schottky Diode
TPS61043 transistor_lvs465.gif Figure 13. Separate Enable and PWM Control Using a Transistor
TPS61043 and_gate_lvs465.gif Figure 14. Separate Enable and PWM Control Using an AND Gate

9.2 Typical Application

TPS61043 typ_app_lvs465.gif
(A) Output capacitor values like 1 µF and larger, reduce the LED ripple current and improve line regulation.
Figure 15. Typical Application Schematic

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 3 as the input parameters.

Table 3. Design Parameters

DESIGN PARAMETER TYPICAL VALUE
Input Voltage 1.8 V to 6 V
Output Voltage VIN to 16 V
Dimming frequency 0.1 to 50 kHz

9.2.2 Detailed Design Procedure

9.2.2.1 Inductor Selection, Maximum Load Current, and Switching Frequency

The PFM peak current control scheme of the TPS61043 is inherently stable. The inductor value does not affect the stability of the regulator. The selection of the inductor together with the nominal LED current, input, and output voltage of the application determines the switching frequency of the converter.

The first step is to calculate the maximum load current the converter can support using the selected inductor. The inductor value has less effect on the maximum available load current and is only of secondary order. A good inductor value to start with is 4.7 µH. Depending on the application, inductor values down to 1 µH can be used. The maximum inductor value is determined by the maximum on time of the switch of 4.5 µs (typical). The peak current limit of 400 mA (typical) must be reached within this 4.5 µs for proper operation. The maximum load current of the converter is determined at the operation point where the converter starts to enter the continuous conduction mode. The converter must always operate in discontinuous conduction mode to maintain regulation.

Depending on the time period of the inductor current fall time being larger or smaller compared to the minimum off time of the converter (400 ns typ), the maximum load current can be calculated.

Inductor fall time:

Equation 9. TPS61043 q_tfall_lvs465.gif

where

  • tf ≥ 400 ns
Equation 10. TPS61043 q_ildmc400_lvs465.gif
Equation 11. TPS61043 q_disccondmd_lvs465.gif

where

  • L = selected inductor value
  • η = expected converter efficiency. Typically between 70% to 85%
Equation 12. TPS61043 q_pkinduccur_lvs465.gif

(Peak inductor current as described in the Peak Current Control (Boost Converter) section)

The above formula contains the expected converter efficiency that allows calculating the expected maximum load current the converter can support. The efficiency can be taken out of the efficiency graphs shown in and or 80% can be used as an accurate estimation.

If the converter can support the desired LED current, the next step is to calculate the converter switching frequency at the operation point, which must be ≤1 MHz. Also the converter switching frequency should be much higher than the applied PWM frequency at the CTRL pin to avoid nonlinear brightness control. Assuming the converter shows no double pulses or pulse bursts (Figure 17 and Figure 18) on the switch node (SW) the switching frequency at the operation point can be calculated as:

Equation 13. TPS61043 q_swtchfrq_lvs465.gif

where

  • ILIM = minimum switch current limit (320 mA typical)
  • L = selected inductor value
  • IO = nominal load or LED current
  • VF = Rectifier diode forward voltage (typically 0.3 V)

The smaller the inductor value, the higher the switching frequency of the converter but the lower the efficiency. The selected inductor must have a saturation current that meets the maximum peak current of the converter as calculated in Peak Current Control (Boost Converter). Use the maximum value for ILIM (480 mA) for this calculation. Another important inductor parameter is the DC resistance. The lower the DC resistance the higher the efficiency of the converter. See Table 4 and Figure 20 to Figure 24 for a selection of inductors.

Table 4. Possible Inductors (or Equivalent)

INDUCTOR VALUE COMPONENT SUPPLIER SIZE
10 µH muRata LQH43CN100K01 4.5 mm × 3.2 mm × 2.6 mm
4.7 µH muRata LQH32CN4R7M11 3.2 mm × 2.5 mm × 2 mm
10 µH Coilcraft DO1605T-103MX 5.5 mm × 4.1 mm × 1.8 mm
4.7 µH Sumida CDRH3D16-4R7 3.8 mm × 3.8 mm × 1.8 mm
3.3 µH Sumida CMD4D11-3R3 3.5 mm × 5.3 mm × 1.2 mm
4.7 µH Sumida CMD4D11-4R7 3.5 mm × 5.3 mm × 1.2 mm
3.3 µH Sumida CMD4D11-3R3 3.5 mm × 5.3 mm × 1.2 mm
4.7 µH Coiltronics SD12-4R7 5.2 mm × 5.2 mm × 1.2 mm
3.3 µH Coilcraft LPO1704-332M 6.6 mm × 5.5 mm × 1 mm
4.7 µH Coilcraft LPO1704-472M 6.6 mm × 5.5 mm × 1 mm

9.2.2.2 Output Capacitor Selection and Line Regulation

For better output voltage filtering, a low ESR output capacitor is recommended. Ceramic capacitors have a low ESR value, but depending on the application, tantalum capacitors can be used.

The selection of the output capacitor value directly influences the output voltage ripple of the converter which also influences line regulation. The larger the output voltage ripple, the larger the line regulation, which means that the LED current changes if the input voltage changes. If a certain change in LED current gives a noticeable change in LED brightness, depends on the LED manufacturer and on the application. Applications requiring good line regulation ≤1%/V (typ) must use output capacitor values ≥1 µF.

See Table 5 and Figure 20 to Figure 24 for the selection of the output capacitor.

Assuming the converter does not show double pulses or pulse bursts (see Figure 17 and Figure 18) on the switch node (SW), the output voltage ripple is calculated as:

Equation 14. TPS61043 q_outvltrip_lvs465.gif

where

  • ILIM(min) = minimum switch current limit (320 mA typical)
  • L = selected inductor value
  • IO = nominal load current
  • fS = switching frequency at the nominal load current as calculated with Equation 13.
  • VF = rectifier diode forward voltage (0.3 V typical)
  • CO = selected output capacitor
  • ESR = output capacitor ESR value

9.2.2.3 Input Capacitor Selection

For good input voltage filtering, low ESR ceramic capacitors are recommended. A 4.7-µF ceramic input capacitor is sufficient for most applications. For better input voltage filtering the capacitor value can be increased. Refer to Table 5 and Figure 20 to Figure 24 for input capacitor selection.

Table 5. Possible Input and Output Capacitors (or Equivalent)

CAPACITOR VOLTAGE RATING COMPONENT SUPPLIER COMMENTS
4.7 µF/X5R/0805 6.3 V Tayo Yuden JMK212BY475MG CI
10 µF/X5R/0805 6.3 V Tayo Yuden JMK212BJ106MG CI
100 nF Any CO
220 nF Any CO
470 nF Any CO
1.0 µF/X7R/1206 25 V Tayo Yuden TMK316BJ105KL CO
1.0 µF/X7R/1206 35 V Tayo Yuden GMK316BJ105KL CO
4.7 µF/X5R/1210 25 V Tayo Yuden TMK325BJ475MG CO

9.2.2.4 Diode Selection

To achieve high efficiency a Schottky diode must be used. The current rating of the diode must meet the peak current rating of the converter as it is calculated in the peak current control section. Use the maximum value for ILIM for this calculation. See Table 6 and Figure 20 to Figure 24 for the Schottky diode selection.

Table 6. Possible Diodes (or Equivalent)

COMPONENT SUPPLIER REVERSE VOLTAGE
ON Semiconductor MBR0530 30 V
ON Semiconductor MBR0520 20 V
Toshiba CRS02 30 V
Zetex ZHCS400 40 V

9.2.3 Application Curves

TPS61043 Softstart_lvs441.gif Figure 16. Soft-Start
TPS61043 Burstmodeop_lvs441.gif Figure 18. Bust Mode Operation
TPS61043 Pfmop_lvs441.gif Figure 17. PFM Operation
TPS61043 Bcwpwmdim_lvs441.gif Figure 19. PWM Dimming

9.3 System Examples

9.3.1 TPS61043 With 1-mm Total System Height

TPS61043 is designed from 3 V to 6 V input for driving LED with 1-mm total system height.

TPS61043 totsyshght1_lvs465.gif Figure 20. TPS61043 With 1-mm Total System Height

9.3.2 TPS61043 With Low LED Ripple Current and Higher Accuracy Using a 4.7-µF Output Capacitor

TPS61043 is designed from 3 V to 6 V input for driving LED with low LED ripple current and higher accuracy using a 4.7-µF output capacitor.

TPS61043 lowrip4out_lvs465.gif Figure 21. TPS61043 With Low LED Ripple Current and Higher Accuracy Using a 4.7-µF Output Capacitor

9.3.3 TPS61043 Powering 3 LEDs

TPS61043 is designed from 3 V to 6 V input for driving 3 LEDs in series.

TPS61043 prwing8led_lvs465.gif Figure 22. TPS61043 Powering 3 LEDs

9.3.4 Adjustable Brightness Control Using an Analog Voltage

TPS61043 is designed from 3 V to 6 V input for driving LED with adjustable brightness control using an analog voltage.

TPS61043 analogvlt_lvs465.gif Figure 23. Adjustable Brightness Control Using an Analog Voltage

9.3.5 Alternative Adjustable Brightness Control Using PWM Signal

TPS61043 is designed for driving LED with adjustable brightness control using an analog voltage.

TPS61043 pwmsignal_lvs465.gif Figure 24. Alternative Adjustable Brightness Control Using PWM Signal