Driving high power LEDs at 350mA with low cost LED controller IC ILD4035 01_00 | Jul 20, 2011 | PDF | 1.63 mb

Driving High Power LEDs at 350mA
with Low Cost LED Controller IC
ILD4035
Application Note 215
http://www.infineon.com/lowcostleddriver
Rev. 1.1, 2011-08-12
Power Management & Multimarket
Edition 2011-08-12
Published by
Infineon Technologies AG
81726 Munich, Germany
© 2011 Infineon Technologies
AG All Rights Reserved.
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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 AN215
Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
Application Note AN215
Revision History: 20 Jul 2011
Previous Revision: Previous_Revision_Number
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Subjects (major changes since last revision)
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Application Note AN215
Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
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............................................................................................. 15
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
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
ILD4035 ................................................................................................................................................ 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 waveform .............................................................................................................................. 9
Maximum Contrast Ratio vs Dimming frequency (100:1=1% Duty) .................................................... 9
Analog Dimming Characteristic ........................................................................................................... 9
ILED vs Vs (Rs=0.303 , L=100 H) ................................................................................................. 11
ILED vs Vs (Rs=0.333 , L=100 H) ................................................................................................. 11
ILED vs Vs (Rs=0.367 , L=100 H) ................................................................................................. 11
Frequency vs Vs (Rs=0.303 , L=100 H) ........................................................................................ 11
Frequency vs Vs (Rs=0.333 , L=100 H) ........................................................................................ 11
Frequency vs Vs (Rs=0.367 , L=100 H) ........................................................................................ 11
Efficiency vs Vs (Rs=0.303 , L=100 H) .......................................................................................... 12
Efficiency vs Vs (Rs=0.333 , L=100 H) .......................................................................................... 12
Efficiency vs Vs (Rs=0.367 , L=100 H) .......................................................................................... 12
ILED vs Ambient Temperature .......................................................................................................... 13
Efficiency vs Ambient Temperature................................................................................................... 13
Soldering Temperature at Vswitch pin vs Ambient Temperature (with the present demo board) ... 13
ILD4035’s total power dissipation at different temperature ........................................................ 14
ILD4035’s power transistor Safe Operating Area for different inductances ............................. 14
Photograph of Demo Board (size of PCB: 50mm x 30mm) .............................................................. 15
PCB Layer Information Top View ...................................................................................................... 15
PCB Layer information Bottom View (unflip) ..................................................................................... 15
Thermal Resistance of PCB-FR4 versus Ground Copper Area ........................................................ 16
Thermal Resistance Representation of the LED-Less Demo Board................................................. 17
List of Tables
Table 1
Table 2
Table 3
Versions of Demo Board for ILD4035 .......................................................................................................... 6
Bill-of-Materials ................................................................................................................................................ 7
Percentage of max LED current vs DC voltage at en/pwm pin .............................................................. 10
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Application Note AN215
Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
1
Introduction
1.1
Features












Wide Input Voltage Range: 4.5 V ... 40 V 
Internal switch for up to 400 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 component required
Small Package: SC74
1.2




Figure 1
ILD4035
Applications
LED driver for general lighting applications 
Retail, office and residential luminaires and downlights 
LED replacement lamps, e.g. MR16 
Architectural lighting 
1.3
Description
This document contains informations about the LED-Less Demonstration Board for ILD4035.
IILD4035 is a hysteretic step-down LED driver. Please refer to the datasheet for the pins descriptions, functions
descriptions and specifications.
The ILD4035 Demonstration Board has two versions. Version ILD4035 24V Board’s sense resistance is
optimized to drive a string of 6 series LEDs at 350mA (max current) with an input voltage of 24V. Version
ILD4035 12V Board’s sense resistance is optimized to drive a string of 3 series LEDs at 350mA (max current)
with an input voltage of 12V.
ILD4035 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 3V. The maximum input voltage for this demonstration
board must not exceed 30V; this restriction is due to the schottky diode installed which has a reverse
breakdown voltage of 30V. If there is a need to test the board with a maximum supply voltage of 40V, please
replace the schottky diode SD1 with a suitable breakdown voltage.
The ILD4035 incorporates the following protection features: Over-voltage protection, temperature protection and
an over-current protection.
The board includes a “Multifunctional Pin” input terminal for digital or analog dimming control signal. PWM
dimming frequencies up to 300Hz at 100:1 contrast ratio and at 100Hz contrast ratio of 300:1 are possible.
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 ILD4035, the sense-resistors
have to be altered to achieve maximum current of 350mA and inductance has to be changed to attain
recommended switching frequencies below 500 kHz.
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
Table 1
Versions of Demo Board for ILD4035
R1
R2
R3
L1
Vs
Board Name
Measured
Vrsense
Suitable
number of
LEDs
Typical
Switch. Freq.
= Vs - VLED+
LED Average
Current
/kHz
/V
/A
/
/
/
/H
/V
ILD4035 12V
Board
1.1
1.1
1.1
100
12
3
133
0.116
0.31
ILD4035 24V
Board
0.91 0.91 0.91
100
24
6
226
0.105
0.34
The above measured values are for typical case only.
1.3.1
Check List before powering up
Before powering on the ILD4035 demonstration board, please verify the following:




Be sure that each LED can conduct 350mA dc current within its safe region of operation. 
Make sure that the input voltage supply is equal to the voltage rating of the board. 
Select the appropriate mode for EN/PWM: 
 to enable the ILD4035 dimming, please force the EN/PWM pin terminal to 3V or up to input voltage,
or 
 to select analog dimming, supply a dc source (0 to 3V) to EN/PWM pin terminal, or 
 to select PWM dimming, supply a PWM signal source (0 to 5V) with frequency within range of
(200Hz to 5 kHz) to EN/PWM pin terminal 
1.3.2
Capacitor C20 for Ripple Reduction
This component C20 is optional and not installed on the standard demo board. This capacitor can help to reduce LED
ripple current. The peak-to-peak ripple current values shown in Table 3 are without C20 installed. Recommended to
1
use low ESR capacitor and its rated voltage must be higher than the maximum input voltage.
1.3.3
Connection of LEDs
2
The ILD4035 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
Open Circuit of terminals LED+ and LED-
If the LED array is disconnected or fails with open state, the ILD4035 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
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.
1
2
Equivalent Series Resistance
Single In-line Package
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
2
Application Information
2.1
Schematic
Figure 2Schematic of the demonstration board
Table 2
Bill-of-Materials
Symbol
Value
Unit
Size
Manufacturer
Comment
L1
100
H
6.3x6.3mm
EPCOS
Shielded Power Inductor ,20%, 1A
R1
*see Table 1
Ω
1206
Part of the current sense resistor
R2
*see Table 1
Ω
1206
Part of the current sense resistor
R3
*see Table 1
Ω
1206
Part of the current sense resistor
R10
0
Ω
0805
Jumper
J1
SD1
0
BAS3010A-03W
Ω
0805
SOD323
INFINEON
Jumper
Medium Power AF Schottky Diode 1A 30V
IC1
ILD4035
SC74
INFINEON
Hysteretic Buck controller and LED driver
C30
4.7
Application Note AN215, 1.3
F
1812
Ceramic, 50V
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
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 2.
2.3
Measured Graphs of the demonstration boards
Unless otherwise specified, the following condition labels apply:
Condition: Vs=12V, Ta=25C
Figure 4
Vsw, Vsense and VLED(-), Vs=12
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Figure 5
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Switching Freq. vs Input Voltage,Vs
20 Jul 2011
Application Note AN215
Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
Figure 6
Dimming waveform
Figure 7
Maximum Contrast Ratio vs Dimming frequency (100:1=1% Duty)
Figure 8
Analog Dimming Characteristic
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
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 0.8V to 2.5V.
Table 3
Percentage of max LED current vs DC voltage at en/pwm pin
Ven_pwm
/V
2.5
Percentage of max. LED Current
/%
< 0.4
0
0.7
10
1.0
25
1.4
50
1.9
75
2.2
90
>2.5
100
PWM Dimming
The EM/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 2.6V or higher. The period of
this PWM signal should be higher than 200s. For the default demo board circuit, a dimming frequency less
than 300Hz is recommended to maintain a maximum contrast ratio of at least 100:1. The maximum contrast
ratio is shown on Figure 7, and the minimum is based on the measured average LED current at 3dB below the
linear reference. The maximum contrast ratio depends largely on the rise time of the inductor current, and hence
is dependent on input voltage, inductor size, and LED string forward voltage. In addition, if C20 is installed, the
maximum contrast ratio or DIM frequency will be further reduced.
2.6
Temperature Protection
ILD4035 incorporates a temperature protection circuit referring to the junction temperature of ILD4035. The
higher the junction temperature of ILD4035 the lower the current of the LEDs. This feature helps to reduce the
power dissipation of ILD4035 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 18. The LED current is reduced by 10% when the ambient temperature
reaches 105°C for 12V, 3LEDs case.
2.7
Setting the nominal LED current
The internal reference for the voltage across the external sense resistor was design to be 0.114V as stated in
the datasheet. A first order approximation for the LED current can be calculated with this formula:
V
I
LED

ISENSE

R R
SENSE
0.114V
SENSE
If a certain level of LED current is desired; the estimation for the Rsense is given by:
V
R
SENSE

I
0.114V
ISENSE
LED

I
LED
The Visense can vary depending on the number of LEDs and voltage supply. Please take reference from
Figure 9, Figure 10, and Figure 11 to help select the Rsense for your application.
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
3
Characteristic Graphs for different Inductors, no. of LEDs, Rs
3.1
ILED, Frequency versus Supply Voltage Characteristics (100H)
Figure 9
ILED vs Vs (Rs=0.303, L=100H)
Figure 12 Frequency vs Vs (Rs=0.303, L=100H)
Figure 10 ILED vs Vs (Rs=0.333, L=100H)
Figure 13 Frequency vs Vs (Rs=0.333, L=100H)
Figure 11 ILED vs Vs (Rs=0.367, L=100H)
Figure 14 Frequency vs Vs (Rs=0.367, L=100H)
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
3.2
Efficiency versus Supply Voltage Characteristics (100H)
Figure 15 Efficiency vs Vs (Rs=0.303, L=100H)
Figure 17 Efficiency vs Vs (Rs=0.367, L=100H)
Figure 16 Efficiency vs Vs (Rs=0.333, L=100H)
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
3.3
Temperature Characteristics (Rs=0.333 L=100uH)
Figure 18 ILED vs Ambient Temperature
Figure 20 Soldering Temperature at Vswitch pin
vs Ambient Temperature (with the
present demo board)
Figure 19 Efficiency vs Ambient Temperature
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
3.4
Power Limitation Characteristic of ILD4035
Figure 21 ILD4035’s total power dissipation at different temperature
Figure 22 ILD4035’s power transistor Safe Operating Area for different inductances
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
4
Evaluation Board and layout Information
Figure 23 Photograph of Demo Board (size of PCB: 50mm x 30mm)
Figure 24 PCB Layer Information Top View
Figure 25 PCB Layer information Bottom View (unflip)
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Driving High Power LEDs at 350mA with Low Cost LED Controller IC ILD4035
4.1
PCB Considerations
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 desired
thermal resistance between solder point temperature and expected ambient temperature, the following chart
can be used.
Figure 26 Thermal Resistance of PCB-FR4 versus Ground Copper Area
The data in the above Figure 26 were measured with following conditions:








Two copper layers, 

2 oz copper (70um thick) and board thickness of about 1.6mm, 

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 350mA with Low Cost LED Controller IC ILD4035
An example where ILD4035’s PCB is separated from LEDs’ PCB and there is not heat transmission between
the two PCBs.
Figure 27 Thermal Resistance Representation of the LED-Less Demo Board
Tj is the junction temperature of the ILD4035’s output transistor connected to switch
pin. Ts is the soldered temperature of the ILD4035’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 ILD4035’s SC74 package.
This is stated as 65K/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 ILD4035 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.
Tj – Ts
Ts – T a
Pd = ------------ = -------------
R
th_js
R
th_sa
With the above equations, and setting Tj (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 26 to correlate the approximated ground copper area required in
PCB layout.
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