SNVS616H April   2009  – July 2015 LM3429 , LM3429-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  Current Regulators
      2. 7.3.2  Predictive Off-Time (PRO) Control
      3. 7.3.3  Switching Frequency
      4. 7.3.4  Average LED Current
      5. 7.3.5  Analog Dimming
      6. 7.3.6  Current Sense and Current Limit
      7. 7.3.7  Control Loop Compensation
      8. 7.3.8  Output Overvoltage Lockout (OVLO)
      9. 7.3.9  Input Undervoltage Lockout (UVLO)
      10. 7.3.10 PWM Dimming
      11. 7.3.11 Startup Regulator (VCC LDO)
      12. 7.3.12 Thermal Shutdown
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Inductor
      2. 8.1.2 LED Dynamic Resistance (rD)
      3. 8.1.3 Output Capacitor
      4. 8.1.4 Input Capacitors
      5. 8.1.5 N-Channel MosFET (NFET)
      6. 8.1.6 Re-Circulating Diode
    2. 8.2 Typical Applications
      1. 8.2.1 Basic Topology Schematics
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1  Operating Point
          2. 8.2.1.2.2  Switching Frequency
          3. 8.2.1.2.3  Average LED Current
          4. 8.2.1.2.4  Inductor Ripple Current
          5. 8.2.1.2.5  LED Ripple Current
          6. 8.2.1.2.6  Peak Current Limit
          7. 8.2.1.2.7  Loop Compensation
          8. 8.2.1.2.8  Input Capacitance
          9. 8.2.1.2.9  NFET
          10. 8.2.1.2.10 Diode
          11. 8.2.1.2.11 Output OVLO
          12. 8.2.1.2.12 Input UVLO
          13. 8.2.1.2.13 PWM Dimming Method
          14. 8.2.1.2.14 Analog Dimming Method
      2. 8.2.2 Buck-Boost Application - 6 LEDs at 1 A
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1  Operating Point
          2. 8.2.2.2.2  Switching Frequency
          3. 8.2.2.2.3  Average LED Current
          4. 8.2.2.2.4  Inductor Ripple Current
          5. 8.2.2.2.5  Output Capacitance
          6. 8.2.2.2.6  Peak Current Limit
          7. 8.2.2.2.7  Loop Compensation
          8. 8.2.2.2.8  Input Capacitance
          9. 8.2.2.2.9  NFET
          10. 8.2.2.2.10 Diode
          11. 8.2.2.2.11 Input UVLO
          12. 8.2.2.2.12 Output OVLO
        3. 8.2.2.3 Application Curve
      3. 8.2.3 Boost PWM Dimming Application - 9 LEDs at 1 A
        1. 8.2.3.1 Detailed Design Procedure
      4. 8.2.4 Buck-Boost Analog Dimming Application - 4 LEDs at 2A
        1. 8.2.4.1 Detailed Design Procedure
      5. 8.2.5 Boost Analog Dimming Application - 12 LEDs at 700 mA
        1. 8.2.5.1 Detailed Design Procedure
      6. 8.2.6 Buck-Boost PWM Dimming Application - 6 LEDs at 500 mA
        1. 8.2.6.1 Detailed Design Procedure
      7. 8.2.7 Buck Application - 3 LEDS at 1.25 A
        1. 8.2.7.1 Detailed Design Procedure
      8. 8.2.8 Buck-Boost Thermal Foldback Application - 8 LEDs at 2.5 A
        1. 8.2.8.1 Detailed Design Procedure
      9. 8.2.9 SEPIC Application - 5 LEDs at 750 mA
        1. 8.2.9.1 Detailed Design Procedure
  9. Power Supply Recommendations
    1. 9.1 Input Supply Current Limit
  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 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Related Links
    4. 11.4 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 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

8.1.1 Inductor

The inductor (L1) is the main energy storage device in a switching regulator. Depending on the topology, energy is stored in the inductor and transfered to the load in different ways (as an example, buck-boost operation is detailed in the Current Regulators section). The size of the inductor, the voltage across it, and the length of the switching subinterval (tON or tOFF) determines the inductor current ripple (ΔiL-PP). In the design process, L1 is chosen to provide a desired ΔiL-PP. For a buck regulator the inductor has a direct connection to the load, which is good for a current regulator. This requires little to no output capacitance therefore ΔiL-PP is basically equal to the LED ripple current ΔiLED-PP. However, for boost and buck-boost regulators, there is always an output capacitor which reduces ΔiLED-PP, therefore the inductor ripple can be larger than in the buck regulator case where output capacitance is minimal or completely absent.

In general, ΔiLED-PP is recommended by manufacturers to be less than 40% of the average LED current (ILED). Therefore, for the buck regulator with no output capacitance, ΔiL-PP should also be less than 40% of ILED. For the boost and buck-boost topologies, ΔiL-PP can be much higher depending on the output capacitance value. However, ΔiL-PP is suggested to be less than 100% of the average inductor current (IL) to limit the RMS inductor current.

L1 is also suggested to have an RMS current rating at least 25% higher than the calculated minimum allowable RMS inductor current (IL-RMS).

8.1.2 LED Dynamic Resistance (rD)

When the load is a string of LEDs, the output load resistance is the LED string dynamic resistance plus RSNS. LEDs are PN junction diodes, and their dynamic resistance shifts as their forward current changes. Dividing the forward voltage of a single LED (VLED) by the forward current (ILED) leads to an incorrect calculation of the dynamic resistance of a single LED (rLED). The result can be 5 to 10 times higher than the true rLED value.

LM3429 LM3429-Q1 30094474.pngFigure 25. Dynamic Resistance

Obtaining rLED is accomplished by referring to the manufacturer's LED I-V characteristic. It can be calculated as the slope at the nominal operating point as shown in Figure 25. For any application with more than 2 series LEDs, RSNS can be neglected allowing rD to be approximated as the number of LEDs multiplied by rLED.

8.1.3 Output Capacitor

For boost and buck-boost regulators, the output capacitor (CO) provides energy to the load when the recirculating diode (D1) is reverse biased during the first switching subinterval. An output capacitor in a buck topology will simply reduce the LED current ripple (ΔiLED-PP) below the inductor current ripple (ΔiL-PP). In all cases, CO is sized to provide a desired ΔiLED-PP. As mentioned in the Inductor section, ΔiLED-PP is recommended by manufacturers to be less than 40% of the average LED current (ILED).

CO should be carefully chosen to account for derating due to temperature and operating voltage. It must also have the necessary RMS current rating. Ceramic capacitors are the best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested.

8.1.4 Input Capacitors

The input capacitance (CIN) provides energy during the discontinuous portions of the switching period. For buck and buck-boost regulators, CIN provides energy during tON and during tOFF, the input voltage source charges up CIN with the average input current (IIN). For boost regulators, CIN only needs to provide the ripple current due to the direct connection to the inductor. CIN is selected given the maximum input voltage ripple (ΔvIN-PP) which can be tolerated. ΔvIN-PP is suggested to be less than 10% of the input voltage (VIN).

An input capacitance at least 100% greater than the calculated CIN value is recommended to account for derating due to temperature and operating voltage. When PWM dimming, even more capacitance can be helpful to minimize the large current draw from the input voltage source during the rising transition of the LED current waveform.

The chosen input capacitors must also have the necessary RMS current rating. Ceramic capacitors are again the best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested.

For most applications, TI recommends bypassing the VIN pin with an 0.1-µF ceramic capacitor placed as close as possible to the pin. In situations where the bulk input capacitance may be far from the LM3429 device, a 10-Ω series resistor can be placed between the bulk input capacitance and the bypass capacitor, creating a 150 kHz filter to eliminate undesired high frequency noise coupling.

8.1.5 N-Channel MosFET (NFET)

The LM3429 requires an external NFET (Q1) as the main power MosFET for the switching regulator. Q1 is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node. In practice, all switching regulators have some ringing at the switch node due to the diode parasitic capacitance and the lead inductance. The current rating is recommended to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the power loss given the RMS transistor current and the NFET on-resistance (RDS-ON).

In general, the NFET should be chosen to minimize total gate charge (Qg) whenever switching frequencies are high and minimize RDS-ON otherwise. This will minimize the dominant power losses in the system. Frequently, higher current NFETs in larger packages are chosen for better thermal performance.

8.1.6 Re-Circulating Diode

A re-circulating diode (D1) is required to carry the inductor current during tOFF. The most efficient choice for D1 is a Schottky diode due to low forward voltage drop and near-zero reverse recovery time. Similar to Q1, D1 is recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe operation during the ringing of the switch node and a current rating at least 10% higher than the average diode current. The power rating is verified by calculating the power loss through the diode. This is accomplished by checking the typical diode forward voltage from the I-V curve on the product data sheet and multiplying by the average diode current. In general, higher current diodes have a lower forward voltage and come in better performing packages minimizing both power losses and temperature rise.

8.2 Typical Applications

8.2.1 Basic Topology Schematics

LM3429 LM3429-Q1 30094422.gifFigure 26. Boost Regulator (VIN < VO)
LM3429 LM3429-Q1 30094451.gifFigure 27. Buck Regulator (VIN > VO)
LM3429 LM3429-Q1 30094450.gifFigure 28. Buck-Boost Regulator

8.2.1.1 Design Requirements

Number of series LEDs: N

Single LED forward voltage: VLED

Single LED dynamic resistance: rLED

Nominal input voltage: VIN

Input voltage range: VIN-MAX, VIN-MIN

Switching frequency: fSW

Current sense voltage: VSNS

Average LED current: ILED

Inductor current ripple: ΔiL-PP

LED current ripple: ΔiLED-PP

Peak current limit: ILIM

Input voltage ripple: ΔvIN-PP

Output OVLO characteristics: VTURN-OFF, VHYSO

Input UVLO characteristics: VTURN-ON, VHYS

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Operating Point

Given the number of series LEDs (N), the forward voltage (VLED) and dynamic resistance (rLED) for a single LED, solve for the nominal output voltage (VO) and the nominal LED string dynamic resistance (rD):

Equation 27. LM3429 LM3429-Q1 30094486.gif
Equation 28. LM3429 LM3429-Q1 30094469.gif

Solve for the ideal nominal duty cycle (D):

Buck

Equation 29. LM3429 LM3429-Q1 30094413.gif

Boost

Equation 30. LM3429 LM3429-Q1 30094414.gif

Buck-boost

Equation 31. LM3429 LM3429-Q1 30094415.gif

Using the same equations, find the minimum duty cycle (DMIN) using maximum input voltage (VIN-MAX) and the maximum duty cycle (DMAX) using the minimum input voltage (VIN-MIN). Also, remember that D' = 1 - D.

8.2.1.2.2 Switching Frequency

Set the switching frequency (fSW) by assuming a CT value of 1 nF and solving for RT:

Buck (Constant Ripple vs. VIN)

Equation 32. LM3429 LM3429-Q1 30094431.gif

Buck (Constant Ripple vs. VO)

Equation 33. LM3429 LM3429-Q1 30094406.gif

Boost and Buck-Boost

Equation 34. LM3429 LM3429-Q1 30094407.gif

8.2.1.2.3 Average LED Current

For all topologies, set the average LED current (ILED) knowing the desired current sense voltage (VSNS) and solving for RSNS:

Equation 35. LM3429 LM3429-Q1 30094411.gif

If the calculated RSNS is too far from a desired standard value, then VSNS must be adjusted to obtain a standard value.

Setup the suggested signal current of 100 µA by assuming RCSH = 12.4 kΩ and solving for RHSP:

Equation 36. LM3429 LM3429-Q1 30094412.gif

If the calculated RHSP is too far from a desired standard value, then RCSH can be adjusted to obtain a standard value.

8.2.1.2.4 Inductor Ripple Current

Set the nominal inductor ripple current (ΔiL-PP) by solving for the appropriate inductor (L1):

Buck

Equation 37. LM3429 LM3429-Q1 EquationL1.gif

Boost and Buck-Boost

Equation 38. LM3429 LM3429-Q1 L1_equation2.gif

To set the worst case inductor ripple current, use VIN-MAX and DMIN when solving for L1.

The minimum allowable inductor RMS current rating (IL-RMS) can be calculated as:

Buck

Equation 39. LM3429 LM3429-Q1 300944a8.gif

Boost and Buck-Boost

Equation 40. LM3429 LM3429-Q1 300944a9.gif

8.2.1.2.5 LED Ripple Current

Set the nominal LED ripple current (ΔiLED-PP), by solving for the output capacitance (CO):

Buck

Equation 41. LM3429 LM3429-Q1 30094418.gif

Boost and Buck-Boost

Equation 42. LM3429 LM3429-Q1 Co_BuckBoost.gif

To set the worst case LED ripple current, use DMAX when solving for CO.

The minimum allowable RMS output capacitor current rating (ICO-RMS) can be approximated:

Buck

Equation 43. LM3429 LM3429-Q1 30094420.gif

Boost and Buck-boost

Equation 44. LM3429 LM3429-Q1 30094421.gif

8.2.1.2.6 Peak Current Limit

Set the peak current limit (ILIM) by solving for the transistor path sense resistor (RLIM):

Equation 45. LM3429 LM3429-Q1 30094410.gif

8.2.1.2.7 Loop Compensation

Using a simple first order peak current mode control model, neglecting any output capacitor ESR dynamics, the necessary loop compensation can be determined.

First, the uncompensated loop gain (TU) of the regulator can be approximated:

Buck

Equation 46. LM3429 LM3429-Q1 30094423.gif

Boost and Buck-Boost

Equation 47. LM3429 LM3429-Q1 30094424.gif

Where the pole (ωP1) is approximated:

Buck

Equation 48. LM3429 LM3429-Q1 30094425.gif

Boost

Equation 49. LM3429 LM3429-Q1 30094426.gif

Buck-Boost

Equation 50. LM3429 LM3429-Q1 30094427.gif

And the RHP zero (ωZ1) is approximated:

Boost

Equation 51. LM3429 LM3429-Q1 30094428.gif

Buck-Boost

Equation 52. LM3429 LM3429-Q1 30094429.gif

And the uncompensated DC loop gain (TU0) is approximated:

Buck

Equation 53. LM3429 LM3429-Q1 30094430.gif

Boost

Equation 54. LM3429 LM3429-Q1 30094432.gif

Buck-Boost

Equation 55. LM3429 LM3429-Q1 30094433.gif

For all topologies, the primary method of compensation is to place a low-frequency dominant pole (ωP2) which will ensure that there is ample phase margin at the crossover frequency. This is accomplished by placing a capacitor (CCMP) from the COMP pin to GND, which is calculated according to the lower value of the pole and the RHP zero of the system (shown as a minimizing function):

Equation 56. LM3429 LM3429-Q1 30094434.gif
Equation 57. LM3429 LM3429-Q1 30094435.gif

If analog dimming is used, CCMP should be approximately 4x larger to maintain stability as the LEDs are dimmed to zero.

A high frequency compensation pole (ωP3) can be used to attenuate switching noise and provide better gain margin. Assuming RFS = 10 Ω, CFS is calculated according to the higher value of the pole and the RHP zero of the system (shown as a maximizing function):

Equation 58. LM3429 LM3429-Q1 30094436.gif
Equation 59. LM3429 LM3429-Q1 30094437.gif

The total system loop gain (T) can then be written as:

Buck

Equation 60. LM3429 LM3429-Q1 30094438.gif

Boost and Buck-boost

Equation 61. LM3429 LM3429-Q1 30094439.gif

8.2.1.2.8 Input Capacitance

Set the nominal input voltage ripple (ΔvIN-PP) by solving for the required capacitance (CIN):

Buck

Equation 62. LM3429 LM3429-Q1 30094440.gif

Boost

Equation 63. LM3429 LM3429-Q1 30094441.gif

Buck-Boost

Equation 64. LM3429 LM3429-Q1 30094442.gif

Use DMAX to set the worst case input voltage ripple, when solving for CIN in a buck-boost regulator and DMID = 0.5 when solving for CIN in a buck regulator.

The minimum allowable RMS input current rating (ICIN-RMS) can be approximated:

Buck

Equation 65. LM3429 LM3429-Q1 30094443.gif

Boost

Equation 66. LM3429 LM3429-Q1 30094444.gif

Buck-Boost

Equation 67. LM3429 LM3429-Q1 30094445.gif

8.2.1.2.9 NFET

The NFET voltage rating should be at least 15% higher than the maximum NFET drain-to-source voltage (VT-MAX):

Buck

Equation 68. LM3429 LM3429-Q1 30094452.gif

Boost

Equation 69. LM3429 LM3429-Q1 30094453.gif

Buck-Boost

Equation 70. LM3429 LM3429-Q1 30094454.gif

The current rating should be at least 10% higher than the maximum average NFET current (IT-MAX):

Buck

Equation 71. LM3429 LM3429-Q1 30094462.gif

Boost and Buck-Boost

Equation 72. LM3429 LM3429-Q1 30094463.gif

Approximate the nominal RMS transistor current (IT-RMS) :

Buck

Equation 73. LM3429 LM3429-Q1 30094464.gif

Boost and Buck-Boost

Equation 74. LM3429 LM3429-Q1 30094465.gif

Given an NFET with on-resistance (RDS-ON), solve for the nominal power dissipation (PT):

Equation 75. LM3429 LM3429-Q1 30094467.gif

8.2.1.2.10 Diode

The Schottky diode voltage rating should be at least 15% higher than the maximum blocking voltage (VRD-MAX):

Buck

Equation 76. LM3429 LM3429-Q1 30094468.gif

Boost

Equation 77. LM3429 LM3429-Q1 30094470.gif

Buck-Boost

Equation 78. LM3429 LM3429-Q1 30094471.gif

The current rating should be at least 10% higher than the maximum average diode current (ID-MAX):

Buck

Equation 79. LM3429 LM3429-Q1 30094472.gif

Boost and Buck-Boost

Equation 80. LM3429 LM3429-Q1 30094473.gif

Replace DMAX with D in the ID-MAX equation to solve for the average diode current (ID). Given a diode with forward voltage (VFD), solve for the nominal power dissipation (PD):

Equation 81. LM3429 LM3429-Q1 30094481.gif

8.2.1.2.11 Output OVLO

For boost and buck-boost regulators, output OVLO is programmed with the turn-off threshold voltage (VTURN-OFF) and the desired hysteresis (VHYSO). To set VHYSO, solve for ROV2:

Equation 82. LM3429 LM3429-Q1 30094484.gif

To set VTURN-OFF, solve for ROV1:

Boost

Equation 83. LM3429 LM3429-Q1 30094485.gif

Buck-Boost

Equation 84. LM3429 LM3429-Q1 30094409.gif

A small filter capacitor (COVP = 47 pF) should be added from the OVP pin to ground to reduce coupled switching noise.

8.2.1.2.12 Input UVLO

For all topologies, input UVLO is programmed with the turn-on threshold voltage (VTURN-ON) and the desired hysteresis (VHYS).

Method #1: If no PWM dimming is required, a two resistor network can be used. To set VHYS, solve for RUV2:

Equation 85. LM3429 LM3429-Q1 30094482.gif

To set VTURN-ON, solve for RUV1:

Equation 86. LM3429 LM3429-Q1 30094483.gif

Method #2: If PWM dimming is required, a three resistor network is suggested. To set VTURN-ON, assume RUV2 = 10 kΩ and solve for RUV1 as in Method #1. To set VHYS, solve for RUVH:

Equation 87. LM3429 LM3429-Q1 300944c3.gif

8.2.1.2.13 PWM Dimming Method

PWM dimming can be performed several ways:

Method #1: Connect the dimming MosFET (Q3) with the drain to the nDIM pin and the source to GND. Apply an external PWM signal to the gate of QDIM. A pull down resistor may be necessary to properly turn off Q3.

Method #2: Connect the anode of a Schottky diode to the nDIM pin. Apply an external inverted PWM signal to the cathode of the same diode.

8.2.1.2.14 Analog Dimming Method

Analog dimming can be performed several ways:

Method #1: Place a potentiometer in series with the RCSH resistor to dim the LED current from the nominal ILED to near zero.

Method #2: Connect a controlled current source as detailed in the Analog Dimming section to the CSH pin. Increasing the current sourced into the CSH node will decrease the LEDs from the nominal ILED to zero current.

8.2.2 Buck-Boost Application - 6 LEDs at 1 A

LM3429 LM3429-Q1 300944i1.gifFigure 29. Buck-Boost Application - 6 LEDs at 1 A Schematic

8.2.2.1 Design Requirements

N = 6

VLED = 3.5 V

rLED = 325 mΩ

VIN = 24 V

VIN-MIN = 10 V

VIN-MAX = 70 V

fSW = 700 kHz

VSNS = 100 mV

ILED = 1A

ΔiL-PP = 500 mA

ΔiLED-PP = 50 mA

ΔvIN-PP = 100 mV

ILIM = 6A

VTURN-ON = 10 V

VHYS = 3 V

VTURN-OFF = 40 V

VHYSO = 10 V

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Operating Point

Solve for VO and rD:

Equation 88. LM3429 LM3429-Q1 300944i2.gif
Equation 89. LM3429 LM3429-Q1 300944i3.gif

Solve for D, D', DMAX, and DMIN:

Equation 90. LM3429 LM3429-Q1 300944i4.gif
Equation 91. LM3429 LM3429-Q1 300944h4.gif
Equation 92. LM3429 LM3429-Q1 300944i5.gif
Equation 93. LM3429 LM3429-Q1 300944i6.gif

8.2.2.2.2 Switching Frequency

Assume CT = 1 nF and solve for RT:

Equation 94. LM3429 LM3429-Q1 300944c4.gif

The closest standard resistor is actually 35.7 kΩ therefore the fSW is:

Equation 95. LM3429 LM3429-Q1 300944c5.gif

The chosen components from step 2 are:

Equation 96. LM3429 LM3429-Q1 300944c6.gif

8.2.2.2.3 Average LED Current

Solve for RSNS:

Equation 97. LM3429 LM3429-Q1 300944c7.gif

Assume RCSH = 12.4 kΩ and solve for RHSP:

Equation 98. LM3429 LM3429-Q1 300944c8.gif

The closest standard resistor for RSNS is actually 0.1Ω and for RHSP is actually 1 kΩ therefore ILED is:

Equation 99. LM3429 LM3429-Q1 300944c9.gif

The chosen components from step 3 are:

Equation 100. LM3429 LM3429-Q1 300944d0.gif

8.2.2.2.4 Inductor Ripple Current

Solve for L1:

Equation 101. LM3429 LM3429-Q1 300944d1.gif

The closest standard inductor is 33 µH therefore the actual ΔiL-PP is:

Equation 102. LM3429 LM3429-Q1 300944d2.gif

Determine minimum allowable RMS current rating:

Equation 103. LM3429 LM3429-Q1 300944d3.gif

The chosen component from step 4 is:

Equation 104. LM3429 LM3429-Q1 300944d4.gif

8.2.2.2.5 Output Capacitance

Solve for CO:

Equation 105. LM3429 LM3429-Q1 300944d5.gif

The closest standard capacitor is 6.8 µF therefore the actual ΔiLED-PP is:

Equation 106. LM3429 LM3429-Q1 300944d6.gif

Determine minimum allowable RMS current rating:

Equation 107. LM3429 LM3429-Q1 300944d7.gif

The chosen components from step 5 are:

Equation 108. LM3429 LM3429-Q1 300944d8.gif

8.2.2.2.6 Peak Current Limit

Solve for RLIM:

Equation 109. LM3429 LM3429-Q1 300944d9.gif

The closest standard resistor is 0.04 Ω therefore ILIM is:

Equation 110. LM3429 LM3429-Q1 300944e0.gif

The chosen component from step 6 is:

Equation 111. LM3429 LM3429-Q1 300944e1.gif

8.2.2.2.7 Loop Compensation

ωP1 is approximated:

Equation 112. LM3429 LM3429-Q1 300944e2.gif

ωZ1 is approximated:

Equation 113. LM3429 LM3429-Q1 300944e3.gif

TU0 is approximated:

Equation 114. LM3429 LM3429-Q1 300944e4.gif

To ensure stability, calculate ωP2:

Equation 115. LM3429 LM3429-Q1 300944e5.gif

Solve for CCMP:

Equation 116. LM3429 LM3429-Q1 300944e6.gif

To attenuate switching noise, calculate ωP3:

Equation 117. LM3429 LM3429-Q1 300944e7.gif

Assume RFS = 10 Ω and solve for CFS:

Equation 118. LM3429 LM3429-Q1 300944e8.gif

The chosen components from step 7 are:

Equation 119. LM3429 LM3429-Q1 300944e9.gif

8.2.2.2.8 Input Capacitance

Solve for the minimum CIN:

Equation 120. LM3429 LM3429-Q1 300944f0.gif

To minimize power supply interaction a 200% larger capacitance of approximately 14 µF is used, therefore the actual ΔvIN-PP is much lower. Because high voltage ceramic capacitor selection is limited, three 4.7 µF X7R capacitors are chosen.

Determine minimum allowable RMS current rating:

Equation 121. LM3429 LM3429-Q1 300944f1.gif

The chosen components from step 8 are:

Equation 122. LM3429 LM3429-Q1 300944f2.gif

8.2.2.2.9 NFET

Determine minimum Q1 voltage rating and current rating:

Equation 123. LM3429 LM3429-Q1 300944f3.gif
Equation 124. LM3429 LM3429-Q1 300944f4.gif

A 100-V NFET is chosen with a current rating of 32A due to the low RDS-ON = 50 mΩ. Determine IT-RMS and PT:

Equation 125. LM3429 LM3429-Q1 300944f6.gif
Equation 126. LM3429 LM3429-Q1 300944f7.gif

The chosen component from step 9 is:

Equation 127. LM3429 LM3429-Q1 300944f8.gif

8.2.2.2.10 Diode

Determine minimum D1 voltage rating and current rating:

Equation 128. LM3429 LM3429-Q1 300944f9.gif
Equation 129. LM3429 LM3429-Q1 300944g0.gif

A 100-V diode is chosen with a current rating of 12 A and VDF = 600 mV. Determine PD:

Equation 130. LM3429 LM3429-Q1 300944g1.gif

The chosen component from step 10 is:

Equation 131. LM3429 LM3429-Q1 300944g2.gif

8.2.2.2.11 Input UVLO

Solve for RUV2:

Equation 132. LM3429 LM3429-Q1 300944g8.gif

The closest standard resistor is 150 kΩ therefore VHYS is:

Equation 133. LM3429 LM3429-Q1 300944g4.gif

Solve for RUV1:

Equation 134. LM3429 LM3429-Q1 300944g5.gif

The closest standard resistor is 21 kΩ making VTURN-ON:

Equation 135. LM3429 LM3429-Q1 300944g6.gif

The chosen components from step 11 are:

Equation 136. LM3429 LM3429-Q1 300944g7.gif

8.2.2.2.12 Output OVLO

Solve for ROV2:

Equation 137. LM3429 LM3429-Q1 300944g9.gif

The closest standard resistor is 499 kΩ therefore VHYSO is:

Equation 138. LM3429 LM3429-Q1 300944h0.gif

Solve for ROV1:

Equation 139. LM3429 LM3429-Q1 300944h1.gif

The closest standard resistor is 15.8 kΩ making VTURN-OFF:

Equation 140. LM3429 LM3429-Q1 300944h2.gif

The chosen components from step 12 are:

Equation 141. LM3429 LM3429-Q1 300944h3.gif

Table 1. Design 1 Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 0.22 µF X7R 10% 25 V MURATA GRM21BR71E224KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
3 CIN 4.7 µF X7R 10% 100 V TDK C5750X7R2A475K
1 CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 100 V 12 A VISHAY 12CWQ10FNPBF
1 L1 33 µH 20% 6.3 A COILCRAFT MSS1278-333MLB
1 Q1 NMOS 100 V 32 A FAIRCHILD FDD3682
1 Q2 PNP 150 V 600 m A FAIRCHILD MMBT5401
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 RLIM 0.04 Ω 1% 1W VISHAY WSL2512R0400FEA
1 ROV1 15.8 kΩ 1% VISHAY CRCW080515K8FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.1 Ω 1% 1W VISHAY WSL2512R1000FEA
1 RT 35.7 kΩ 1% VISHAY CRCW080535K7FKEA
1 RUV1 21 kΩ 1% VISHAY CRCW080521K0FKEA
1 RUV2 150 kΩ 1% VISHAY CRCW0805150KFKEA

8.2.2.3 Application Curve

LM3429 LM3429-Q1 300944b5.gifFigure 30. Buck-Boost Efficiency vs Input Voltage, VO= 6 LEDs

8.2.3 Boost PWM Dimming Application - 9 LEDs at 1 A

LM3429 LM3429-Q1 300944h5.gifFigure 31. Boost PWM Dimming Application - 9 LEDs at 1 A Schematic

8.2.3.1 Detailed Design Procedure

Table 2. Design 2 Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
2 CCMP, CFS 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
2, 1 CIN, CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 60 V 5 A COMCHIP CDBC560-G
1 L1 33 µH 20% 6.3 A COILCRAFT MSS1278-333MLB
1 Q1 NMOS 60 V 8 A VISHAY SI4436DY
1 Q2 NMOS 60 V 115 mA ON SEMI 2N7002ET1G
2 RCSH, ROV1 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 RLIM 0.06 Ω 1% 1 W VISHAY WSL2512R0600FEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.1 Ω 1% 1 W VISHAY WSL2512R1000FEA
1 RT 35.7 kΩ 1% VISHAY CRCW080535K7FKEA
1 RUV1 1.82 kΩ 1% VISHAY CRCW08051K82FKEA
1 RUV2 10 kΩ 1% VISHAY CRCW080510KFKEA
1 RUVH 17.8 kΩ 1% VISHAY CRCW080517K8FKEA

8.2.4 Buck-Boost Analog Dimming Application - 4 LEDs at 2A

LM3429 LM3429-Q1 300944h6.gifFigure 32. Buck-Boost Analog Dimming Application - 4 LEDs at 2 A Schematic

8.2.4.1 Detailed Design Procedure

Table 3. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 1 µF X7R 10% 10 V MURATA GRM21BR71A105KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 50 V MURATA GRM21BR71E104KA01L
2, 1 CIN, CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 60 V 5 A VISHAY CDBC560-G
1 L1 22 µH 20% 7.2 A COILCRAFT MSS1278-223MLB
1 Q1 NMOS 60 V 8 A VISHAY SI4436DY
1 Q2 PNP 150 V 600 mA FAIRCHILD MMBT5401
1 RADJ 1-MΩ potentiometer BOURNS 3352P-1-105
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 RLIM 0.04 Ω 1% 1 W VISHAY WSL2512R0400FEA
1 ROV1 18.2 kΩ 1% VISHAY CRCW080518K2FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.05 Ω 1% 1 W VISHAY WSL2512R0500FEA
1 RT 41.2 kΩ 1% VISHAY CRCW080541K2FKEA
1 RUV1 21 kΩ 1% VISHAY CRCW080521K0FKEA
1 RUV2 150 kΩ 1% VISHAY CRCW0805150KFKEA

8.2.5 Boost Analog Dimming Application - 12 LEDs at 700 mA

LM3429 LM3429-Q1 300944h7.gifFigure 33. Boost Analog Dimming Application - 12 LEDs at 700 mA Schematic

8.2.5.1 Detailed Design Procedure

Table 4. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 1 µF X7R 10% 10 V MURATA GRM21BR71A105KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 50 V MURATA GRM21BR71E104KA01L
2, 1 CIN, CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 100 V 12 A VISHAY 12CWQ10FNPBF
1 L1 47 µH 20% 5.3 A COILCRAFT MSS1278-473MLB
1 Q1 NMOS 100 V 32 A FAIRCHILD FDD3682
1 Q2 NPN 40 V 200 mA FAIRCHILD MMBT3904
1 Q3, Q4 (dual pack) Dual PNP 40 V 200 mA FAIRCHILD FFB3906
1 RADJ 100 kΩ potentiometer BOURNS 3352P-1-104
1 RBIAS 40.2 kΩ 1% VISHAY CRCW080540K2FKEA
1 RCSH, ROV1, RUV1 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1.05 kΩ 1% VISHAY CRCW08051K05FKEA
1 RLIM 0.06 Ω 1% 1 W VISHAY WSL2512R0600FEA
1 RMAX 4.99 kΩ 1% VISHAY CRCW08054K99FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.15 Ω 1% 1 W VISHAY WSL2512R1500FEA
1 RT 35.7 kΩ 1% VISHAY CRCW080535K7FKEA
1 RUV2 100 kΩ 1% VISHAY CRCW0805100KFKEA
1 VREF 5 V precision reference TI LM4040

8.2.6 Buck-Boost PWM Dimming Application - 6 LEDs at 500 mA

LM3429 LM3429-Q1 300944h9.gifFigure 34. Buck-Boost PWM Dimming Application - 6 LEDs at 500 mA

8.2.6.1 Detailed Design Procedure

Table 5. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 0.68 µF X7R 10% 25 V MURATA GRM21BR71E684KA88L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
3 CIN 4.7 µF X7R 10% 100 V TDK C5750X7R2A475K
1 CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 100 V 12 A VISHAY 12CWQ10FNPBF
1 D2 Schottky 30 V 500 mA ON SEMI BAT54T1G
1 L1 68 µH 20% 4.3 A COILCRAFT MSS1278-683MLB
1 Q1 NMOS 100 V 32 A VISHAY FDD3682
1 Q2 PNP 150 V 600 mA FAIRCHILD MMBT5401
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 ROV1 15.8 kΩ 1% VISHAY CRCW080515K8FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.2 Ω 1% 1 W VISHAY WSL2512R2000FEA
1 RT 35.7 kΩ 1% VISHAY CRCW080535K7FKEA
1 RUV1 1.43 kΩ 1% VISHAY CRCW08051K43FKEA
1 RUV2 10 kΩ 1% VISHAY CRCW080510K0FKEA
1 RUVH 17.4 kΩ 1% VISHAY CRCW080517K4FKEA

8.2.7 Buck Application - 3 LEDS at 1.25 A

LM3429 LM3429-Q1 300944h8.gifFigure 35. Buck Application - 3 LEDS at 1.25 A Schematic

8.2.7.1 Detailed Design Procedure

Table 6. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 0.015 µF X7R 10% 50 V MURATA GRM21BR71H153KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.01 µF X7R 10% 50 V MURATA GRM21BR71H103KA01L
2 CIN 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 CO 1 µF X7R 10% 50 V TDK C4532X7R1H105K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 60V 5 A COMCHIP CDBC560-G
1 L1 22 µH 20% 7.3 A COILCRAFT MSS1278-223MLB
1 Q1 NMOS 60 V 8 A VISHAY SI4436DY
1 Q2 PNP 150 V 600 mA FAIRCHILD MMBT5401
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RT 49.9 kΩ 1% VISHAY CRCW080549K9FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
1 RLIM 0.04 Ω 1% 1 W VISHAY WSL2512R0400FEA
1 ROV1 21.5 kΩ 1% VISHAY CRCW080521K5FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.08 Ω 1% 1 W VISHAY WSL2512R0800FEA
1 RUV1 11.5 kΩ 1% VISHAY CRCW080511K5FKEA
1 RUV2 100 kΩ 1% VISHAY CRCW0805100KFKEA

8.2.8 Buck-Boost Thermal Foldback Application - 8 LEDs at 2.5 A

LM3429 LM3429-Q1 300944i0.gifFigure 36. Buck-Boost Thermal Foldback Application - 8 LEDs at 2.5 A Schematic

8.2.8.1 Detailed Design Procedure

Table 7. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
3 CIN 4.7 µF X7R 10% 100 V TDK C5750X7R2A475K
1 CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 100 V 12 A VISHAY 12CWQ10FNPBF
1 L1 22 µH 20% 7.2 A COILCRAFT MSS1278-223MLB
1 Q1 NMOS 100 V 32 A FAIRCHILD FDD3682
1 Q2 PNP 150 V 600 mA FAIRCHILD MMBT5401
2 RCSH, ROV1 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 1 kΩ 1% VISHAY CRCW08051K00FKEA
2 RLIM, RSNS 0.04 Ω 1% 1 W VISHAY WSL2512R0400FEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RT 49.9 kΩ 1% VISHAY CRCW080549K9FKEA
1 RUV1 13.7 kΩ 1% VISHAY CRCW080513K7FKEA
1 RUV2 150 kΩ 1% VISHAY CRCW0805150KFKEA

8.2.9 SEPIC Application - 5 LEDs at 750 mA

LM3429 LM3429-Q1 300944i8.gifFigure 37. 5 LEDs at 750 mA

8.2.9.1 Detailed Design Procedure

Table 8. Bill of Materials

QTY PART ID PART VALUE MANUFACTURER PART NUMBER
1 LM3429 Boost controller TI LM3429MH
1 CCMP 0.47 µF X7R 10% 25 V MURATA GRM21BR71E474KA01L
1 CF 2.2 µF X7R 10% 16 V MURATA GRM21BR71C225KA12L
1 CFS 0.1 µF X7R 10% 25 V MURATA GRM21BR71E104KA01L
2, 1 CIN, CO 6.8 µF X7R 10% 50 V TDK C4532X7R1H685K
1 COV 47 pF COG/NPO 5% 50 V AVX 08055A470JAT2A
1 CSEP 1 µF X7R 10% 100 V TDK C4532X7R2A105K
1 CT 1000 pF COG/NPO 5% 50 V MURATA GRM2165C1H102JA01D
1 D1 Schottky 60 V 5 A COMCHIP CDBC560-G
1 L1, L2 68 µH 20% 4.3 A COILCRAFT DO3340P-683
1 Q1 NMOS 60 V 8 A VISHAY SI4436DY
1 Q2 NMOS 60 V 115 mA ON SEMI 2N7002ET1G
1 RCSH 12.4 kΩ 1% VISHAY CRCW080512K4FKEA
1 RFS 10 Ω 1% VISHAY CRCW080510R0FKEA
2 RHSP, RHSN 750 Ω 1% VISHAY CRCW0805750RFKEA
1 RLIM 0.04 Ω 1% 1 W VISHAY WSL2512R0400FEA
2 ROV1, RUV1 15.8 kΩ 1% VISHAY CRCW080515K8FKEA
1 ROV2 499 kΩ 1% VISHAY CRCW0805499KFKEA
1 RSNS 0.1 Ω 1% 1 W VISHAY WSL2512R1000FEA
1 RT 49.9 kΩ 1% VISHAY CRCW080549K9FKEA
1 RUV2 100 kΩ 1% VISHAY CRCW0805100KFKEA