SNVS678F June   2010  – November 2015 LM3414 , LM3414HV

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 Pulse-Level-Modulation (PLM) Operation Principles
      2. 7.3.2 Minimum Switch ON-time
      3. 7.3.3 Peak Switch Current Limit
      4. 7.3.4 PWM Dimming Control
      5. 7.3.5 Analog Dimming Control
      6. 7.3.6 Internal VCC Regulator
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Setting the Switching Frequency
      2. 8.1.2 Setting LED Current
      3. 8.1.3 Inductor Selection
    2. 8.2 Typical Applications
      1. 8.2.1 LM3414/HV Design Example
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Calculate Operating Parameters
          2. 8.2.1.2.2 Calculate RIADJ
          3. 8.2.1.2.3 Calculate RFS
          4. 8.2.1.2.4 Calculate LMIN
          5. 8.2.1.2.5 Calculate CIN-MIN
      2. 8.2.2 LM3414/HV Design Example (IOUT = 1 A)
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Calculate Operating Parameters
          2. 8.2.2.2.2 Calculate RIADJ
          3. 8.2.2.2.3 Calculate RFS
          4. 8.2.2.2.4 Calculate LMIN
          5. 8.2.2.2.5 Calculate CIN-MIN
        3. 8.2.2.3 Application Curve
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Related Links
    2. 11.2 Community Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 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 Setting the Switching Frequency

Both the LM3414 and LM3414HV are PWM LED drivers that contain a clock generator to generate constant switching frequency for the device. The switching frequency is determined by the resistance of an external resistor RFS in the range of 250 kHz to 1 MHz. Lower resistance of RFS results in higher switching frequency. The switching frequency of the LM3414/HV is governed using Equation 5.

Equation 5. LM3414 LM3414HV 30124830.gif
LM3414 LM3414HV 30124845.gif Figure 20. Switching Frequency vs RFS

Table 1. Examples for fSW Settings

fSW (kHz) RFS (kΩ)
250 80
500 40
1000 20

To ensure accurate current regulation, the LM3414/HV should be operated in continuous conduction mode (CCM) and the ON time should not be shorter than 400 ns under all operation condition.

8.1.2 Setting LED Current

The LM3414/HV requires no external current sensing resistor for LED current regulation. The average output current of the LM3414/HV is adjustable by varying the resistance of the resistor, RIADJ that connects across the IADJ and GND pins. The IADJ pin is internally biased to 1.255 V. The LED current is then governed by Equation 6.

Equation 6. LM3414 LM3414HV 30124831.gif

where

  • 350 mA < ILED < 1A
LM3414 LM3414HV 30124861.gif Figure 21. LED Current vs RIADJ

Table 2. Examples for IOUT Settings

IOUT (mA) RIADJ (kΩ)
350 8.93
500 6.25
700 4.46
1000 3.13

The LED current can be set to any level in the range from 350 mA to 1A. To provide accurate LED current, RIADJ should be a resistor with no more than 0.5% tolerance. If the IADJ pin is accidentally shorted to GND (RIADJ = 0), the output current is limited to avoid damaging the circuit. When the overcurrent protection is activated, current regulation cannot be maintained until the overcurrent condition is cleared.

8.1.3 Inductor Selection

To ensure proper output current regulation, the LM3414/HV must operate in Continuous Conduction Mode (CCM). With the incorporation of PLM, the peak-to-peak inductor current ripple can be set as high as ±60% of the defined average output current. The minimum inductance of the inductor is decided by the defined average LED current and allowable inductor current ripple. The minimum inductance can be found by the equations shown in Equation 7 through Equation 8.

Because:

Equation 7. LM3414 LM3414HV 30124833.gif

Thus:

Equation 8. LM3414 LM3414HV 30124834.gif

The LM3414/HV can maintain LED current regulation without output filter capacitor. This is because the inductor of the floating buck structure provides continuous current to the LED throughout the entire switching cycle. When LEDs are driven without filter capacitor, the LED peak current must not set exceeding the rated current of the LED. The peak LED current is governed by Equation 9.

Equation 9. LM3414 LM3414HV 30124835.gif

8.2 Typical Applications

8.2.1 LM3414/HV Design Example

LM3414 LM3414HV 30124801.gif Figure 22. LM3414/HV Design Example Schematic

8.2.1.1 Design Requirements

  • Input Voltage: VIN
  • LED String Voltage: VLED
  • LED Current: ILED
  • Switching Frequency: fSW
  • Maximum LED Current Ripple: ΔiL-PP
  • Maximum Input Voltage Ripple: ΔVIN

8.2.1.2 Detailed Design Procedure

8.2.1.2.1 Calculate Operating Parameters

To calculate component values the operating duty cycle (D) must be calculated using Equation 10.

Equation 10. LM3414 LM3414HV appex_D_eq_snvs678.gif

8.2.1.2.2 Calculate RIADJ

To get the desired LED current calculate the value for RIADJ using Equation 11.

Equation 11. LM3414 LM3414HV appex_Radj_eq_snvs678.gif

8.2.1.2.3 Calculate RFS

Calculate the value of RFS for the desired switching frequency using Equation 12.

Equation 12. LM3414 LM3414HV appex_Rfs_eq_snvs678.gif

8.2.1.2.4 Calculate LMIN

Calculate the minimum inductor value required for the desired LED current ripple using Equation 13.

Equation 13. LM3414 LM3414HV appex_Lmin_eq_snvs678.gif

8.2.1.2.5 Calculate CIN-MIN

Calculate the minimum input capacitor value for the desired input voltage ripple using Equation 14.

Equation 14. LM3414 LM3414HV appex_Cmin_eq_snvs678.gif

8.2.2 LM3414/HV Design Example (IOUT = 1 A)

LM3414 LM3414HV 30124828.gif Figure 23. LM3414/HV Design Example (IOUT = 1 A) Schematic

8.2.2.1 Design Requirements

  • Input Voltage: VIN = 48 V ±10%
  • LED String Voltage: VLED = 35 V
  • LED Current: ILED = 1 A
  • Switching Frequency: fSW = 500 kHz
  • Maximum LED Current Ripple: ΔiL-PP ≤ 500 mA
  • Maximum Input Voltage Ripple: ΔVIN ≤ 200 mV

8.2.2.2 Detailed Design Procedure

8.2.2.2.1 Calculate Operating Parameters

To calculate component values the operating duty cycle (D) for this application can be calculated be calculated using Equation 15.

Equation 15. LM3414 LM3414HV desex_D_eq_snvs678.gif

8.2.2.2.2 Calculate RIADJ

For 1A LED current calculate the value for RIADJ using Equation 16.

Equation 16. LM3414 LM3414HV desex_Radj_eq_snvs678.gif

Choose a standard value of RIADJ = 3.24kΩ.

8.2.2.2.3 Calculate RFS

Calculate the value of RFS for 500-kHz switching frequency using Equation 17.

Equation 17. LM3414 LM3414HV desex_Rfs_eq_snvs678.gif

Choose a standard value of RFS = 40.2kΩ.

8.2.2.2.4 Calculate LMIN

Calculate the minimum inductor value required for 500 mA or less peak-to-peak LED current ripple using Equation 18.

Equation 18. LM3414 LM3414HV desex_Lmin_eq_snvs678.gif

Choose a higher standard value of L = 47µH.

8.2.2.2.5 Calculate CIN-MIN

Calculate the minimum input capacitor value for 200 mV or less input voltage ripple using Equation 19.

Equation 19. LM3414 LM3414HV desex_Cmin_eq_snvs678.gif

Choose a higher standard value of CIN = 2.2µF.

Table 3. Bill of Materials

DESIGNATION DESCRIPTION PACKAGE MANUFACTURE PART NO. VENDOR
U1 LED Driver IC
LM3414 / LM3414HV
SOIC-8 LM3414 / LM3414HV TI
L1 Inductor 47 µH 8 × 8 × 4.9 (mm) MMD-08EZ-470M-SI Mag.Layers
D1 Schottky Diode 100 V, 2 A SMP SS2PH10-M3 Vishay
CIN Cap MLCC 100V 2.2 µF X7R 1210 GRM32ER72A225KA35L Murata
CVCC Cap MLCC 16V 1 µF X5R 603 GRM39X5R105K16D52K Murata
RIADJ Chip Resistor 3.24 kΩ 1% 603 CRCW06033241F Vishay
RFS Chip Resistor 40.2 kΩ 1% 603 CRCW06034022F Vishay

8.2.2.3 Application Curve

LM3414 LM3414HV tek00007.gif Figure 24. PWM Dimming Top = DIM. Bottom = LED Current.