Driving high power LEDs at 700mA with LED controller IC ILD4120 01_00 | Sep 13, 2011 | PDF | 1.42 mb

Driving High Power LEDs at 700mA
with LED Controller IC
ILD4120
Application Note 270
http://www.infineon.com/lowcostleddriver
Rev. 1.1, 2011-09-13
Power Management & Multimarket
Edition 2011-09-13
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2011 Infineon Technologies
AG All Rights Reserved.
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IMPLEMENTATION OF THE INFINEON TECHNOLOGIES COMPONENT ONLY AND SHALL NOT BE
REGARDED AS ANY DESCRIPTION OR WARRANTY OF A CERTAIN FUNCTIONALITY, CONDITION OR
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NOTE MUST VERIFY ANY FUNCTION DESCRIBED HEREIN IN THE REAL APPLICATION. INFINEON
TECHNOLOGIES HEREBY DISCLAIMS ANY AND ALL WARRANTIES AND LIABILITIES OF ANY KIND
(INCLUDING WITHOUT LIMITATION WARRANTIES OF NON-INFRINGEMENT OF INTELLECTUAL
PROPERTY RIGHTS OF ANY THIRD PARTY) WITH RESPECT TO ANY AND ALL INFORMATION GIVEN IN
THIS APPLICATION NOTE.
Information
For further information on technology, delivery terms and conditions and prices, please contact the nearest
Infineon Technologies Office (www.infineon.com).
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Application Note AN270
Driving High Power LEDs at 700mA with LED Controller IC ILD4120
Application Note AN270
Revision History: 13 September 2011
Previous Revision: Previous_Revision_Number
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Subjects (major changes since last revision)
Application Note AN270, 0.4
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Application Note AN270
Driving High Power LEDs at 700mA with LED Controller IC ILD4120
Table of Contents
1
Introduction ..................................................................................................................................................... 5
2
Application Information............................................................................................................................... 7
3
Characteristic Graphs for different Inductors, no. of LEDs, Rs...................................................... 11
4
Evaluation Board and layout Information............................................................................................. 14
List of Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
ILD4120 ................................................................................................................................................ 5
Schematic of the demonstration board ................................................................................................ 7
Measurement setup for measuring Vsense voltage w.r.t. Vs pin ........................................................ 8
Vsw, Vsense and VLED(-), Vs=12 ...................................................................................................... 8
Switching Freq. vs Input Voltage,Vs .................................................................................................... 8
Dimming Waveforms ........................................................................................................................... 9
Maximum Contrast Ratio vs Dimming Frequency (100:1=1% duty) ................................................... 9
Analog Dimming Characteristic ........................................................................................................... 9
ILED vs Vs (Rs=0.187 , L=68µH) ................................................................................................... 11
ILED vs Vs (Rs=0.100 , L=33µH) .................................................................................................... 11
Frequency vs Vs (Rs=0.187 , L=68µH) ........................................................................................... 11
Frequency vs Vs (Rs=0.100 , L=33µH) ........................................................................................... 11
Efficiency vs Vs (Rs=0.187 , L=68µH) ............................................................................................. 12
Efficiency vs Vs (Rs=0.100 , L=33µH) ............................................................................................. 12
I_LED vs Ambient Temperature ....................................................................................................... 13
Efficiency vs Ambient Temperature................................................................................................... 13
Solder Point Temperature vs Ambient Temperature......................................................................... 13
Photograph of Demo Board (size of PCB: 50mm x 30mm) .............................................................. 14
PCB Layer Information Top View ...................................................................................................... 14
PCB Layer information Bottom View (unflip) ..................................................................................... 14
Thermal Resistance of PCB-FR4 versus Ground Copper Area ........................................................ 15
Thermal Resistance .......................................................................................................................... 16
List of Tables
Table 1
Table 2
Table 3
Demo Board for ILD4120 ............................................................................................................................... 6
Bill-of-Materials ................................................................................................................................................ 7
Percentage of max LED current vs DC voltage at PWM pin .................................................................. 10
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Application Note AN270
Driving High Power LEDs at 700mA with LED Controller IC ILD4120
1
Introduction
1.1
Features












Wide Input Voltage Range: 4.5 V ... 40 V 
Internal switch for up to 1200 mA average LED
current 
Over current protection 
Over voltage protection 
Temperature protection mechanism 
Inherent open-circuit LED protection 
Soft- Start capability 
Low shut down current 
Analog and PWM dimming possible 
Typical 3% output current accuracy 
Minimum external components required 
Package: DSO-8 with exposed pad
1.2




Figure 1
ILD4120
Applications
LED driver for general lighting applications 
Retail, office and residential luminaires and downlights 
LED replacement lamps 
Architectural lighting 
1.3
Description
This document contains informations about the LED-Less Demonstration Board for ILD4120.
ILD4120 is a hysteretic buck LED driver IC for industrial applications. Please refer to the datasheet for the pins
descriptions, functions descriptions and specifications.
ILD4120 maintains a constant current through a string of LEDS as long as the input voltage exceeds the sum of
the forward voltages of the LEDs in the string by at least 3 V. The maximum input voltage for this demonstration
board must not exceed 30 V due to the board is optimizing for the 30 V operation. If there is a need to test the
board with a maximum supply voltage of 40 V, please replace the schottky diode SD1 with a suitable breakdown
voltage.
The ILD4120 incorporates the following protection features: Over-voltage protection, temperature shut down
and an over-current protection.
The board includes a “PWM” input terminal for digital or analog dimming control signal. PWM dimming
frequencies upto 300 Hz at 100:1 3 dB contrast ratio and at 100 Hz 3 dB contrast ratio of 300:1 are possible.
Higher LED current dimming ratios can be still achieved if higher deviations between PWM duty cycle and LED
current ratio are accepted.
The demonstration board is designed to operate at ambient temperatures up to 100 °C.
The complete demonstration board schematic is shown in
curves are shown in Figure 4 to Figure 8.
Figure 2. Typical waveforms and performance
Although a wide variety of LED combinations and currents can be driven with the ILD4120, the sense-resistors
have to be altered to achieve maximum current of 1200 mA and inductance has to be changed to attain
recommended switching frequencies below 500 kHz.
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
Table 1
Demo Board for ILD4120
R1
R2
R3
L1
Vs
Board
Name
/
ILD4120
Demoboard
/
/
0.56 0.56 0.56
/H
/V
68
12
Suitable
number of
LEDs
3
Typical
Switch.
Freq.
Measured
Vrsense =
Vs - VLED+
LED
Average
Current
/kHz
/V
/A
77
0.117
0.625
The above measured values are for typical case only.
1.3.1
Check List before powering up
Before powering on the ILD4120 demonstration board, please verify the following:



Be sure that each LED can conduct 600 mA DC current within its safe region of operation. 
Make sure that the input voltage supply is less than 30 V. 
Select the appropriate mode for EN/PWM: 
 to enable the ILD4120, please force the EN pin terminal to 2.5 V or more, and 
 to select analog dimming, supply a dc source (0 to 3 V) to PWM pin terminal, or 
 to select PWM dimming, supply a PWM signal source from 0 V to 2.5 V. 

1.3.2
Capacitor C20 for Ripple Reduction
This capacitor C20 is optional and not installed on the standard demo board. The capacitor can help to reduce
1
LED ripple current. Recommended to use low ESR capacitor and its rated voltage must be higher than the
maximum input voltage.
1.3.3
Connection of LEDs
2
The ILD4120 demo board includes a 3-pin SIP connector for the anode connection (LED +) and a 2-pin SIP
connector for the cathode connection (LED -) of the “LEDs in series”. The anode connection is labeled as CON1-
3 and cathode connection is labeled as CON2-1 on the board.
1.3.4
PWM Dimming
The PWM terminal on the PCB is an input for the pulse width modulated (PWM) signal to control the dimming of
the LED string. The PWM signal’s logic high level should be at least 2.5 V or higher. For the default demo board
circuit, a dimming frequency less than 300 Hz is recommended to maintain a 3 dB contrast ratio of at least
100:1. The 3 dB contrast ratio is shown on Figure 7, and the minimum is based on the measured average LED
current at 3 dB below the linear reference. Higher LED current dimming ratios can be still achieved if higher
deviations between PWM duty cycle and LED current ratio are accepted. The achievable dimming ratio of the
LED current depends mainly on the rise and fall time of the LED current and is thus dependent on supply
voltage, LED string forward voltage and inductance value. In addition, if C20 is installed, the maximum contrast
ratio or DIM frequency will be further reduced.
1.3.5
Open Circuit of terminals LED+ and LED-
If the LED array is disconnected or fails with open state, the ILD4120 will operate at 100% duty cycle. The
output voltage (at LED+) will rise to the level of the input voltage. The other output terminal (LED -) will fall to
1
2
Equivalent Series Resistance
Single In-line Package
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
ground. Note that under the above said condition; please avoid reconnecting the LED array between LED+ and
LED- terminals without powering down first. This precaution is to avoid excessive surge current that may
damage the LEDs in the case when C20 is assembled.
2
Application Information
2.1
Schematic
Figure 2Schematic of the demonstration board
Table 2
Bill-of-Materials
Symbol
Value
Unit
Size
Manufacturer
Comment
L1
68
µH
7.3x7.3mm
EPCOS
Shielded Power Inductor, 20%, 0.82 A
R1
0.56
Ω
1206
Part of the current sense resistor
R2
0.56
Ω
1206
Part of the current sense resistor
R3
0.56
Ω
1206
Part of the current sense resistor
R10
SD1
IC1
0
BAS3020B
ILD4120
Ω
0805
SOT363
DSO-8
C30
4.7
µF
Application Note AN270, 0.4
Jumper
INFINEON
INFINEON
1812
Medium Power AF Schottky Diode 2 A 30 V
Hysteretic Buck controller and LED driver
Ceramic, 50 V
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
2.2
Recommended method to measure Vsense w.r.t. Vs pin
Figure 3
Measurement setup for measuring Vsense voltage w.r.t. Vs pin
By probing Vsense pin voltage with reference to Vs pin, it facilitates the observation and measurement of the
ripple and average of Vsense voltage at the same time with “Oscilloscope set to DC coupling”, and without
offsetting the DC voltage. This is shown in Figure 4, waveform 3.
2.3
Measured Graphs of the demonstration boards
Unless otherwise specified, the following condition labels apply:
Condition 12 V: Vs = 12 V, Ta = 25 C
Figure 4
Figure 5
Vsw, Vsense and VLED(-), Vs=12
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Switching Freq. vs Input Voltage,Vs
13 September 2011
Application Note AN270
Driving High Power LEDs at 700mA with LED Controller IC ILD4120
Figure 6
Dimming Waveforms
Figure 7
3 dB Contrast Ratio vs Dimming
Frequency (100:1=1% duty)
Application Note AN270, 0.4
Figure 8 Analog Dimming Characteristic
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
2.4
Analog Dimming Characteristic
The analog dimming characteristic graph is shown Figure 8. To achieve a linear change in LED current versus
control voltage, the recommended range of voltage at EN/PWM pin is from 0.8 V to 2.5 V.
Table 3
Percentage of max LED current vs DC voltage at PWM pin
Ven_pwm
/V
2.5
Percentage of max. LED Current
/%
< 0.5
0.8
0
10
1.1
1.5
25
50
1.9
2.2
75
90
>2.5
100
Temperature Protection
ILD4120 incorporates a temperature protection circuit referring to the junction temperature of ILD4120. The
higher the junction temperature of ILD4120 the lower the current of the LEDs. This feature helps to reduce the
power dissipation of ILD4120 and the LEDs. Yet still the product specific maximum ratings for junction
temperature need to be observed to avoid a permanent damage of the devices. The ILED temperature
characteristic is shown on Figure 15. The LED current is reduced by 10% when the ambient temperature
reaches 90 °C for 12 V, 3 LEDs case.
2.6
Setting the nominal LED current
The internal reference for the voltage across the external sense resistor was design to be 0.117 V as stated in
the datasheet. A first order approximation for the LED current can be calculated with this formula:
V
I LED 
sense
R

sense
0.117 V
R
sense
If a certain level of LED current is desired; the estimation for the Rsense is given by:
V
R sense 
sense
I
LED

0.117 V
I
LED
The Vsense can vary depending on the number of LEDs and voltage supply. Please take reference from Figure
9 and Figure 10.
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
3
Characteristic Graphs for different Inductors, no. of LEDs, Rs
3.1
ILED, Switching Frequency versus Supply Voltage Characteristics
Figure 9
ILED vs Vs (Rs=0.187, L=68µH)
Figure 10 ILED vs Vs (Rs=0.100, L=33µH)
1
Figure 11 Frequency vs Vs (Rs=0.187, L=68µH)
1
Figure 12 Frequency vs Vs (Rs=0.100, L=33µH)
1
For Rs=0.100Ω, the operating voltage range needs to
be checked not to violate absolute maximum rating of
the IC.
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
3.2
Efficiency versus Supply Voltage Characteristics
Figure 13 Efficiency vs Vs (Rs=0.187, L=68µH)
Figure 14 Efficiency vs Vs (Rs=0.100, L=33µH)
1
1
For Rs=0.100Ω, the operating voltage range needs
to be checked not to violate absolute maximum
rating of the IC.
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
3.3
Temperature Characteristics (Rs=0.187 L=68µH)
Figure 15 I_LED vs Ambient Temperature
Figure 17 Solder Point Temperature vs Ambient
Temperature.
Figure 16 Efficiency vs Ambient Temperature
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
4
Evaluation Board and Layout Information
Figure 18 Photograph of Demo Board (size of PCB: 50mm x 30mm)
Figure 19 PCB Layer Information Top View
Figure 20 PCB Layer information Bottom View (unflip)
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
4.1
PCB Consideration
The free-wheeling diode’s path from inductor to Vs pin of the integrated circuit is recommended to be as
short a distance as possible. This is to minimize oscillation in the system.
The energy storage capacitor between Vs and Gnd is recommended to be placed as near to the IC as possible.
This helps to stabilize the supply voltage when the IC draws large instantanoeus current during switching.
Ground plane should be as large as possible to improve heat dissipation.
As a reference for designing the surface area for the grounding for the PCB using FR4 to achieve a certain
thermal resistance between desired solder point temperature and expected ambient temperature, the following
chart can be used.
Figure 21 Thermal Resistance of PCB-FR4 versus Ground Copper Area
The data in the above Figure 21 were measured with following conditions:








Two copper layers. 

2 oz copper (70 µm thick) and board thickness of about 1.6 mm. 

Ground pin connection of the IC is used to dissipate heat. 

FR4 material. 

No forced convection. 

No heat sink. 

No special mask opening for improved heat dissipation. 

In the chart, only three points are marked by diamond symbol. These are measured data. The broken
line represents intermediate points which can de derived by linear interpolation. 
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Driving High Power LEDs at 700mA with LED Controller IC ILD4120
An example where ILD4120’s PCB is separated from LED PCB and there is not heat transmission
between the two PCBs.
Figure 22 Thermal Resistance
Tj is the junction temperature of the ILD4120’s output transistor connected to switch pin.
Ts is the soldered temperature of the ILD4120’s ground pin to FR4-PCB.
Ta is the ambient temperature.
Rth_js is the thermal resistance from junction to soldered point with reference to ILD4120’s DSO-8 package.
This is stated as 15 K/W in the datasheet.
Rth_sa is the thermal resistance from soldered point to ambient which is dependent on size of grounding area of
PCB.
Pd is the power dissipated by ILD4120 which is approximately 10% of total power from supply (for rough
calculation), or it can be derived by (Total power from supply – LEDs’ power – Power Loss on other external
components).
The above variables are related in the equations on the next line.
P
d

T j  Ts
R
th _ js

T T
s
R
a
th _ sa
With the above equations, and setting T j (recommended to be below 100 °C), the Ts can be calculated.
By choosing a desired Ta, the Rth_sa can be calculated.
With the calculated Rth_sa, reference Figure 21 to correlate the approximated ground copper area required in
PCB layout.
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