SNVS533D September   2007  – November 2014 LM4510

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 Handling 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 Short Circuit Protection
      2. 7.3.2 Feedback Fault Protection
      3. 7.3.3 Input Undervoltage Lock-Out
      4. 7.3.4 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Non-Synchronous Operation
      2. 7.4.2 Operation in Synchronous Continuous Conduction Mode (Cycle 1, Cycle 2)
        1. 7.4.2.1 Cycle 1 Description
        2. 7.4.2.2 Cycle 2 Description
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 2.7 V to 5.5 V Input with a 16 V Output
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Adjusting Output Voltage
          2. 8.2.1.2.2 Maximum Output Current
          3. 8.2.1.2.3 Inductor Selection
          4. 8.2.1.2.4 IL_AVE Check
          5. 8.2.1.2.5 Input Capacitor Selection
          6. 8.2.1.2.6 Output Capacitor Selection
          7. 8.2.1.2.7 Soft-Start Function and Soft-Start Capacitor Selection
          8. 8.2.1.2.8 Compensation Component Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Flash and Torch Application
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
        3. 8.2.2.3 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 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

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 LM4510 shuts down when the EN pin is low. In this mode the feedback resistors and the load are disconnected from the input in order to avoid leakage current flow and to allow the output voltage to drop to 0 V.

The LM4510 turns on when EN is high. There is an internal pull-down resistor on the EN pin so the device is in a normally off state.

8.2 Typical Applications

8.2.1 2.7 V to 5.5 V Input with a 16 V Output

30031001.gifFigure 18. Typical Application Circuit for Normal DC/DC

8.2.1.1 Design Requirements

The LM4510 is designed to operate up to 75 mA at 2.7 V input and 350 mA at 5.5 V input to output 16 V. In any case, it is recommended to avoid starting up the device at minimum input voltage and maximum load. Special attention must be taken to avoid operating near thermal shutdown condition. A simple calculation can be used to determine the power dissipation at the operating condition. PD-MAX = (TJ-MAX-OP – TA-MAX)/RθJA(TJ-MAX-OP = 125°C).

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Adjusting Output Voltage

The output voltage is set using the feedback pin and a resistor voltage divider (RF1, RF2) connected to the output as shown in Figure 18.

The ratio of the feedback resistors sets the output voltage.

    RF2 Selection

    First of all choose a value for RF2 generally between 10 kΩ and 25 kΩ.

    RF1 Selection

    Calculate RF1 using Equation 1:

    Equation 1. 30031017.gif

Table 1 gives suggested component values for several typical output voltages.

Table 1. Suggested Component Values for Different Output Voltages

OUTPUT VOLTAGE (V) RF2 (kΩ) RF1 (kΩ) RC (kΩ) CC1 (nF)
16 20.5 240 46.4 2.2
12 20.5 174 46.4 2.2
5 20.5 60.4 46.4 2.2
3.3 20.5 33 46.4 2.2

8.2.1.2.2 Maximum Output Current

When the output voltage is set at different level, it is important to know the maximum load capability. By first order estimation, IOUT(MAX) can be estimated by Equation 2:

Equation 2. 30031097.gif

8.2.1.2.3 Inductor Selection

The larger value inductor makes lower peak inductor current and reduces stress on internal power NMOS.

On the other hand, the smaller value inductor has smaller outline, lower DCR and a higher current capacity. Generally a 4.7-μH to 15-μH inductor is recommended.

8.2.1.2.4 IL_AVE Check

The average inductor current is given by Equation 3:

Equation 3. 30031018.gif

Where IOUT is output current, η is the converter efficiency of the total driven load and D’ is the off duty cycle of the switching regulator.

Inductor DC current rating (40°C temperature rise) should be more than the average inductor current at worst case.

ΔI Define

The inductor ripple current is given by Equation 4:

Equation 4. 30031019.gif

Where D is the on-duty cycle of the switching regulator. A common choice is to set ΔIL to about 30% of IL_AVE.

IL_PK≤ ICL Check & IMIN Define

The peak inductor current is given by Equation 5:

Equation 5. 30031020.gif

To prevent loss of regulation, ensure that the NMOS power switch current limit is greater than the worst-case peak inductor current in the target application.

Also make sure that the inductor saturation current is greater than the peak inductor current under the worst-case load transient, high ambient temperature and start-up conditions. Refer to Table 2 for suggested inductors.

Table 2. Suggested Inductors and Their Suppliers

MODEL VENDOR DIMENSIONS LxWxH (mm) D.C.R (max)
DO3314-472ML COILCRAFT 3.3mm x 3.3mm x 1.4mm 320 mΩ
DO3316P-472ML COILCRAFT 12.95mm x 9.4mm x 5.4mm 18 mΩ

8.2.1.2.5 Input Capacitor Selection

Due to the presence of an inductor, the input current waveform is continuous and triangular. So the input capacitor is less critical than output capacitor in boost applications. Typically, a 4.7-μF to 10-μF ceramic input capacitor is recommended on the VIN pin of the IC.

ICIN_RMS Check

The RMS current in the input capacitor is given by Equation 6:

Equation 6. 30031021.gif

The input capacitor should be capable of handling the RMS current.

8.2.1.2.6 Output Capacitor Selection

The output capacitor in a boost converter provides all the output current when the switch is closed and the inductor is charging. As a result, it sees very large ripple currents.

A ceramic capacitor of value 4.7 μF to 10 μF is recommended at the output. If larger amounts of capacitance are desired for improved line support and transient response, tantalum capacitors can be used.

ICOUT_RMS Check

The RMS current in the output capacitor is given by Equation 7:

Equation 7. 30031022.gif

The output capacitor should be capable of handling the RMS current.

The ESR and ESL of the output capacitor directly control the output ripple. Use capacitors with low ESR and ESL at the output for high efficiency and low ripple voltage. The output capacitor also affects the soft-start time (See Soft-Start Function and Soft-Start Capacitor Selection). Table 3 shows suggested input and output capacitors.

Table 3. Suggested CIN and COUT Capacitors and Their Suppliers

MODEL TYPE VENDOR VOLTAGE RATING CASE SIZE
INCH (mm)
4.7 µF for CIN
C2012X5R0J475 Ceramic, X5R TDK 6.3 V 0805 (2012)
GRM21BR60J475 Ceramic, X5R muRata 6.3 V 0805 (2012)
JMK212BJ475 Ceramic, X5R Taiyo-Yuden 6.3 V 0805 (2012)
C2012X5R0J475K Ceramic, X5R TDK 6.3 V 0603 (1608)
10 µF for COUT
TMK316BJ106KL Ceramic, X5R Taiyo-Yuden 25 V 1206 (3216)
12103D106KAT2A Ceramic, X5R AVX 25 V 1210 (3225)

8.2.1.2.7 Soft-Start Function and Soft-Start Capacitor Selection

The LM4510 has a soft-start pin that can be used to limit the input inrush current. Connect a capacitor from SS pin to GND to set the soft-start period. Figure 19 describes the soft start process.

  • Initial charging period: When the device is turned on, the control circuitry linearly regulating initial charge current charges VOUT by limiting the inrush current.
  • Soft-start period: After VOUT reaches VIN –0.7 V (typ.), the device starts switching and the CS is charged at a constant current of 11 μA, ramping up to VIN. This period ends when VSS reaches VFB. CS should be large enough to ensure soft-start period ends after CO is fully charged.

During the initial charging period, the required load current must be smaller than the initial charge current to ensure VOUT reaches VIN –0.7 V (typ.).

30031023.gifFigure 19. Soft-Start Timing Diagram

CS Selection

The soft-start time without load can be estimated as:

Equation 8. 30031024.gif

Where the IINIT_CHARGE is Initial Charging Current depending on VIN and ISS_CHARGE (11 μA (typ.). Also, when selecting the fuse current rating, make sure the value is higher than the initial charging current.

8.2.1.2.8 Compensation Component Selection

The LM4510 provides a compensation pin COMP to customize the voltage loop feedback. It is recommended that a series combination of RC and CC1 be used for the compensation network, as shown in the typical application circuit. In addition, CC2 is used for compensating high frequency zeros.

The series combination of RC and CC1 introduces a pole-zero pair according to Equation 9:

Equation 9. 30031025.gif

In addition, CC2 introduces a pole according to Equation 10:

Equation 10. 30031026.gif

Where RO is the output impedance of the error amplifier, approximately 1 MΩ, and amplifier voltage gain is typically 200 V/V depending on temperature and VIN.

Refer to Table 4 for suggested soft start capacitor and compensation components.

Table 4. Suggested CS and Compensation Components

MODEL TYPE VENDOR VOLTAGE RATING CASE SIZE
INCH (mm)
(CS) C1608C0G1E103J Ceramic, X5R TDK 6.3 V 603 (1608)
(C1)TMK107SD222JA-T Ceramic, X5R Taiyo Yuden 25 V 603 (1608)
(RC) 9t06031A4642FBHFT Resistor Yageo Corporation 1/10 W 603 (1608)

8.2.1.3 Application Curves

30031030.gifFigure 20. Efficiency vs Output Current (VOUT = 16 V)
30031032.gif
Figure 22. Efficiency vs Output Current (VOUT = 5 V, L= DO3314-472ML)
30031009.pngFigure 24. Shut Down (VOUT = 16 V, RLOAD = 940 Ω)
30031031.gifFigure 21. Efficiency vs Output Current (VOUT = 12 V)
30031007.pngFigure 23. Start Up (VOUT = 16 V, RLOAD = 530 Ω)

8.2.2 Flash and Torch Application

LM4510 can be configured to drive white LEDs for the flash and torch functions. The flash/torch can be set up with the circuit shown in Figure 25 by using the resistor RT to determine the current in Torch Mode and RF to determine the current in Flash Mode. The amount of current can be estimated using Equation 11:

Equation 11. 30031027.gif
30031028.gifFigure 25. Typical Application Circuit for Flash/Torch

8.2.2.1 Design Requirements

See Design Requirements.

8.2.2.2 Detailed Design Procedure

See Detailed Design Procedure.

8.2.2.3 Application Curve

See Application Curves.