SGLS276D January   2005  – March 2016 TPS61040-Q1 , TPS61041-Q1

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  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. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Peak Current Control
      2. 7.3.2 Soft Start
      3. 7.3.3 Enable
      4. 7.3.4 Undervoltage Lockout
      5. 7.3.5 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Inductor Selection, Maximum Load Current
        2. 8.2.2.2 Setting The Output Voltage and Feed-Forward Capacitor
        3. 8.2.2.3 Line and Load Regulation
        4. 8.2.2.4 Output Capacitor Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Diode Selection
      3. 8.2.3 Application Curves
    3. 8.3 System Examples
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Related Links
    3. 11.3 Community Resource
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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8 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.

8.1 Application Information

The TPS6104x-Q1 is designed for output voltages up to 28 V with an input voltage range of 1.8 V to 6 V. TPS61040-Q1 can operate up to 400-mA typical peak load current and TPS61040-Q1 can operate up to 250-mA typical peak load current. The device operates in a pulse-frequency-modulation (PFM) scheme with constant peak-current control. This control scheme maintains high efficiency over the entire load current range, and with a switching frequency up to 1 MHz, the device enables the use of very small external components.

8.2 Typical Application

The following section provides a step-by-step design approach for configuring the TPS61040-Q1 as a voltage-regulating boost converter for LCD bias supply, as shown in Figure 12.

TPS61040-Q1 TPS61041-Q1 ai_lcd_gls276.gif Figure 12. LCD Bias Supply

8.2.1 Design Requirements

Table 2 lists the design parameters for this example.

Table 2. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Input Voltage 1.8 V to 6 V
Output Voltage 18 V
Output Current 10 mA

8.2.2 Detailed Design Procedure

8.2.2.1 Inductor Selection, Maximum Load Current

Because the PFM peak-current control scheme is inherently stable, the inductor value does not affect the stability of the regulator. The selection of the inductor together with the nominal load current, input and output voltage of the application determines the switching frequency of the converter. Depending on the application, TI recommends inductor values from 2.2 µH to 47 µH. The maximum inductor value is determined by the maximum ON-time of the switch, typically 6 µs. The peak current limit of 400 mA (typically) must be reached within this
6-µs period for proper operation.

The inductor value determines the maximum switching frequency of the converter. Therefore, select the inductor value that ensures the maximum switching frequency at the converter maximum load current is not exceeded. The maximum switching frequency is calculated using Equation 2.

Equation 2. TPS61040-Q1 TPS61041-Q1 Q2_lvs413.gif

where

  • IP = Peak current as described in Peak Current Control
  • L = Selected inductor value
  • VIN(min) = The highest switching frequency occurs at the minimum input voltage

If the selected inductor value does not exceed the maximum switching frequency of the converter, the next step is to calculate the switching frequency at the nominal load current using Equation 3:

Equation 3. TPS61040-Q1 TPS61041-Q1 Q3_lvs413.gif

where

  • IP = Peak current as described in Peak Current Control
  • L = Selected inductor value
  • Iload = Nominal load current
  • Vd = Rectifier diode forward voltage (typically 0.3 V)

A smaller inductor value gives a higher converter switching frequency, but lowers the efficiency.

The inductor value has less effect on the maximum available load current and is only of secondary order. The best way to calculate the maximum available load current under certain operating conditions is to estimate the expected converter efficiency at the maximum load current. This number can be taken out of the efficiency graphs shown in Figure 1, Figure 2, Figure 3, and Figure 4. The maximum load current can then be estimated using Equation 4.

Equation 4. TPS61040-Q1 TPS61041-Q1 Q4_lvs413.gif

where

  • IP = Peak current as described in Peak Current Control
  • L = Selected inductor value
  • fS(max) = Maximum switching frequency as calculated previously
  • η = Expected converter efficiency. Typically 70% to 85%.

The maximum load current of the converter is the current at the operation point where the converter starts to enter the continuous conduction mode. Usually the converter should always operate in discontinuous conduction mode.

Last, the selected inductor must have a saturation current that exceeds the maximum peak current of the converter (as calculated in Peak Current Control). Use the maximum value for ILIM for this calculation.

Another important inductor parameter is the DC resistance. The lower the DC resistance, the higher the efficiency of the converter. Table 3 lists few typical inductors for LCD Bias Supply design (see Figure 12), but customers must verify and validate them to check whether they are suitable for their application.

Table 3. Typical Inductors for LCD Bias Supply (see Figure 12)

DEVICE INDUCTOR VALUE COMPONENT SUPPLIER COMMENTS
TPS61040-Q1 10 μH Sumida CDRH3D16-100 High efficiency
10 μH Murata LQH4C100K04 High efficiency
4.7 μH Sumida CDRH3D16-4R7 Small solution size
4.7 μH Murata LQH3C4R7M24 Small solution size
TPS61041-Q1 10 μH Murata LQH3C100K24 High efficiency
Small solution size

8.2.2.2 Setting The Output Voltage and Feed-Forward Capacitor

The output voltage is calculated as:

Equation 5. TPS61040-Q1 TPS61041-Q1 Q5_gls276.gif

For battery-powered applications, a high impedance voltage divider must be used with a typical value for R2 of ≤200 kΩ and a maximum value for R1 of 2.2 MΩ. Smaller values can be used to reduce the noise sensitivity of the feedback pin.

A feed-forward capacitor across the upper feedback resistor R1 is required to provide sufficient overdrive for the error comparator. Without a feed-forward capacitor, or one whose value is too small, the TPS6104x-Q1 shows double pulses or a pulse burst instead of single pulses at the switch node (SW), causing higher output voltage ripple. If this higher output voltage ripple is acceptable, the feed-forward capacitor can be left out.

The lower the switching frequency of the converter, the larger the feed-forward capacitor value required. A good starting point is to use a 10-pF feed-forward capacitor. As a first estimation, the required value for the feed-forward capacitor at the operation point can also be calculated using Equation 6.

Equation 6. TPS61040-Q1 TPS61041-Q1 Q6_gls276.gif

where

  • R1 = Upper resistor of voltage divider
  • fS = Switching frequency of the converter at the nominal load current (see Inductor Selection, Maximum Load Current for calculating the switching frequency)
  • CFF = Choose a value that comes closest to the result of the calculation

The larger the feed-forward capacitor the worse the line regulation of the device. Therefore, when concern for line regulation is paramount, the selected feed-forward capacitor must be as small as possible. See the next section for more information about line and load regulation.

8.2.2.3 Line and Load Regulation

The line regulation of the TPS6104x-Q1 depends on the voltage ripple on the feedback pin. Usually a 50-mV peak-to-peak voltage ripple on the feedback pin FB gives good results.

Some applications require a very tight line regulation and can only allow a small change in output voltage over a certain input voltage range. If no feed-forward capacitor CFF is used across the upper resistor of the voltage feedback divider, the device has the best line regulation. Without the feed-forward capacitor the output voltage ripple is higher because the TPS6104x-Q1 shows output voltage bursts instead of single pulses on the switch pin (SW), increasing the output voltage ripple. Increasing the output capacitor value reduces the output voltage ripple.

If a larger output capacitor value is not an option, a feed-forward capacitor CFF can be used as described in the previous section. The use of a feed-forward capacitor increases the amount of voltage ripple present on the feedback pin (FB). The greater the voltage ripple on the feedback pin (≥50 mV), the worse the line regulation. There are two ways to improve the line regulation further:

  1. Use a smaller inductor value to increase the switching frequency which will lower the output voltage ripple, as well as the voltage ripple on the feedback pin.
  2. Add a small capacitor from the feedback pin (FB) to ground to reduce the voltage ripple on the feedback pin down to 50 mV again. As a starting point, the same capacitor value as selected for the feed-forward capacitor CFF can be used.

8.2.2.4 Output Capacitor Selection

For best output voltage filtering, TI recommends a low ESR output capacitor. Ceramic capacitors have a low ESR value but tantalum capacitors can be used as well, depending on the application.

Assuming the converter does not show double pulses or pulse bursts on the switch node (SW), the output voltage ripple can be calculated using Equation 7.

Equation 7. TPS61040-Q1 TPS61041-Q1 Q7_gls276.gif

where

  • IP = Peak current as described in the Peak Current Control section
  • L = Selected inductor value
  • Iout = Nominal load current
  • fS (Iout) = Switching frequency at the nominal load current as calculated previously
  • Vd = Rectifier diode forward voltage (typically 0.3 V)
  • Cout = Selected output capacitor
  • ESR = Output capacitor ESR value

Table 4 lists few typical capacitors for LCD Bias Supply design (see Figure 12), but customers must verify and validate them to check whether they are suitable for their application.

Table 4. Typical Input and Output Capacitors for LCD Bias Supply Design (See Figure 12)

DEVICE CAPACITOR VOLTAGE RATING COMPONENT SUPPLIER COMMENTS
TPS6104x-Q1 4.7 μF/X5R/0805 6.3 V Taiyo Yuden JMK212BY475MG CIN
10 μF/X5R/0805 6.3 V Taiyo Yuden JMK212BJ106MG CIN
1 μF/X7R/1206 25 V Taiyo Yuden TMK316BJ105KL COUT
1 μF/X5R/1206 35 V Taiyo Yuden GMK316BJ105KL COUT
4.7 μF/X5R/1210 25 V Taiyo Yuden TMK325BJ475MG COUT

8.2.2.5 Input Capacitor Selection

For good input voltage filtering, TI recommends low-ESR ceramic capacitors. A 4.7-μF ceramic input capacitor is sufficient for most of the applications. For better input voltage filtering this value can be increased. See Table 4 and the Typical Application section for input capacitor recommendations.

8.2.2.6 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 section peak current control. Use the maximum value for ILIM for this calculation. Table 5 lists the few typical Schottky Diodes for LCD Bias Supply design shown in Figure 12. Customers must verify and validate them, however, to check whether they are suitable for their application.

Table 5. Typical Schottky Diodes for LCD Bias Supply Design (See Figure 12)

DEVICE REVERSE VOLTAGE COMPONENT SUPPLIER COMMENTS
TPS6104x-Q1 30 V ON Semiconductor MBR0530
20 V ON Semiconductor MBR0520
20 V ON Semiconductor MBRM120L High efficiency
30 V Toshiba CRS02

8.2.3 Application Curves

TPS61040-Q1 TPS61041-Q1 tc_line_gls276.gif
Figure 13. Line Transient Response
TPS61040-Q1 TPS61041-Q1 tc_start_gls276.gif
Figure 15. Start-Up Behavior
TPS61040-Q1 TPS61041-Q1 tc_load_gls276.gif
Figure 14. Load Transient Response

8.3 System Examples

Figure 16 to Figure 22 shows the different possible power supply designs with the TPS6104x-Q1 devices. However, these circuits must be fully validated and tested by customers before they actually use them in their designs. TI does not warrant the accuracy or completeness of these circuits, nor does TI accept any responsibility for them.

TPS61040-Q1 TPS61041-Q1 ai_bias_gls276.gif Figure 16. LCD Bias Supply With Adjustable Output Voltage
TPS61040-Q1 TPS61041-Q1 ai_lcd2_gls276.gif Figure 17. LCD Bias Supply With Load Disconnect
TPS61040-Q1 TPS61041-Q1 ai_pos_gls276.gif Figure 18. Positive and Negative Output LCD Bias Supply
TPS61040-Q1 TPS61041-Q1 ai_stan_gls276.gif Figure 19. Standard 3.3-V to 12-V Supply
TPS61040-Q1 TPS61041-Q1 ai_dual_gls276.gif Figure 20. Dual Battery Cell to 5-V/50-mA Conversion
Efficiency Approximately Equals 84% at VIN = 2.4 V to VO = 5 V/45 mA
TPS61040-Q1 TPS61041-Q1 ai_white_gls276.gif Figure 21. White-LED Supply With Adjustable Brightness Control
Using a PWM Signal on the Enable Pin Efficiency Approx. Equals 86% at VIN = 3 V, ILED = 15 mA
TPS61040-Q1 TPS61041-Q1 ai_white2_gls276.gif
A. A smaller output capacitor value for C2 causes a larger LED ripple.
Figure 22. White-LED Supply With Adjustable Brightness Control
Using an Analog Signal on the Feedback Pin