EVB10803 DataSheet DownloadLink 4836

Evaluation board EVB10803
Power LED driver for automotive applications
1.
Scope
This document describes the design and use of the MLX10803 evaluation board. For a general description about
the functionality of the MLX10803 please refer to the MLX10803 data sheet.
Note: Evaluation boards produced before Q1 2006 use the MLX10803A. Some resistor values and corresponding
parameters differ from the circuit presented in this document. Please consult the MLX10803 internet product page
at http://www.melexis.com for the latest updates.
2.
Applications
The MLX10803 evaluation board is intended to be used as an application example of the MLX10803 Power LED
driver. It was developed to demonstrate the features of the circuit and is suitable to be used in prototypes and
mock ups to allow quick implementation of the MLX10803 in a LED lighting application.
3.
Other Components Needed
LED(s):
- all High Brightness LEDs, e.g.:
Lumileds Luxeon® , Lumileds Luxeon III
Cree XLamp™ 3 7090 series, Cree XLamp™ 7090 series
OSRAM (Advanced) Power TOPLED® , OSRAM Golden Dragon®
Nichia POWER LED Series
Optional NTC: - external temperature sensor
4.
Standard NTC thermistor with RT=25°C = 100kΩ..470kΩ
Application Circuit
Figure 1: Evaluation board schematic
390121080301
20/Mar/2006
Author: SSZ
Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
5.
Connector Pin Definitions
Connector J1 (Supply)
Signal
Connection
Pin1
Pin2
Pin3
Pin4
Pin5
Pin6
Connector J2 (LED)
VBAT
GND
VS/PWM
GND
VREF
GND
Signal
general load and IC supply, 6..32V DC
supply ground
Separate IC supply for PWM usage
Additional ground for VS/PWM signal
Voltage reference input VREF
Additional ground for VREF signal
Connection
Pin1
Pin2
Connector J3 (NTC)
LED+
LEDSignal
High Brightness LED(s) anode
High Brightness LED(s) cathode
Connection
Pin1
Pin2
Ext. NTC
Ext. NTC
External NTC for temperature down regulation
Note: signals in bold are compulsory
6.
PCB Layout
J1 Pinout (Supply)
J3 Pinout (NTC)
Pin1
Pin2
Pin3
Pin4
Pin5
Pin6
VBAT
GND
VS/PWM
GND
VREF
GND
Pin1
Pin2
external NTC
external NTC
J2 Pinout (LED)
Pin1
Pin2
LED(s)+ (anode)
LED(s)- (cathode)
Figure 2: Evaluation board dimensions and locations
390121080301
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Author: SSZ
Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
7.
Minimal Board Connections
For normal operation only a few connections are necessary. The supply line VBAT must be connected to
any standard DC supply. The input voltage should always be about 2V higher then the sum of all
LED forward voltages in order to keep the regulator working. The supply must be able to drive the peak LED
current that is defined with the IREF2 potentiometer.
The LED(s) is (are) connected to the board via a polarised plug to avoid incorrect connection.
Figure 3: Minimal board connections
8.
Description
For details on the function of the LED driver circuit, please refer to the MLX10803 IC specification.
8.1.
General
For standard applications without the use of PWM, the jumper JMP1 has to be set in order to supply the IC
directly from the VBAT line. This is the default setting.
The LED(s) must be connected to J2, anode to LED+ (Pin1) and cathode to LED- (Pin2).
Supply voltage (6..32V DC) is applied to J1, Pin1 while Pin2 is the corresponding GND connection.
The sense resistor R3 was selected in order to limit the maximum peak current to about 2 Ampere. That was done
to remain within the operation area (saturation current Isat) of the selected coil. Thus, the average LED current is
limited to values about 1.5 Ampere depending on the used settings. If higher currents are desired, care has to be
taken with the selection of coil and transistor and attention has to be drawn to the thermal behaviour of the board.
8.2.
Using PWM
Dimming the average LED current is achieved by applying a PWM signal to the VS/PWM pin (J1, Pin3). In fact, the
IC is powered on and off according to the state of the duty cycle. Because of the maximum IC settling time, the
maximum PWM frequency is limited to 5kHz. The on voltage of the PWM signal must be 6..32V in order to power
the IC correctly. The PWM signal must be able to drive the IC’s supply current which is maximum 700µA @13.8V
and 2mA @32V.
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Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
In PWM mode, the jumper JMP1 must be removed to open the connection to VBAT!
Please note that there is no polarity protection in the PWM line! The user has to ensure the
correct polarity of the PWM signal!
8.3.
Using the VREF input as a second peak current threshold level
The VREF input is intended to be used to set an optional voltage reference for the RSENSE peak current threshold
level. It acts in the same way as IREF1 and IREF2 inputs but has no internal pull up current sources. Thus, the
voltage at VREF must be applied from extern. If the voltage level at VREF becomes lower then the voltages on
IREF1 and IREF2, this voltage becomes dominant and is used (divided by 5) as the RSENSE current threshold
level. With that feature, it is possible to have a 2nd LED current/light output as it is used for example in combined
tail/break lights.
Whether this pin is an analogue input, it can also be used as an alternative, digital PWM input. The user has to
ensure that the voltage level during the ON state is higher then the dominant level on pins IREF1/IREF2. As the
highest possible voltage on both IREF pins can be 3.8V, a PWM signal with a signal amplitude of 5V (standard
logic or µC output) is best suited.
Furthermore, the OFF time signal amplitude has to be < 20mV, as any higher level on that pin is interpreted as
voltage input level and used for setting the RSENSE current threshold level.
As default, the VREF pin is externally pulled up to VS by a 470k resistor. This way, the VREF pin is always
recessive (“H”) in case it is not used.
8.4.
Using an external NTC as temperature sensor
In order to avoid destruction of the LED(s) due to overheating, the MLX10803 offers the possibility for a
temperature down regulation. Via connector J3, a NTC resistor can be connected as a temperature sensor. For
best results, the NTC should be thermally connected to the LED(s).
The NTC is connected to the IREF2 Pin of the MLX10803. For a quick adaptation to a certain application, the PCB
consists of two unpopulated 0805 pads for a serial and a parallel resistor (R6, R7). With these resistors, the
regulation starting point can be manipulated as desired. As default, the pad for the series resistor (R7) is shortcut
by a thin PCB trace. If a series resistor should be used, this trace has to be cut off before it is populated.
If temperature down regulation should be used, the parameters monoflop time (by potentiometer R4, ROSC) and
LED peak current (by potentiometer R5, IREF2) have to be adjusted first.
The voltage on pin IREF2 is measured and taken as a reference to define the starting point for the temperature
down regulation.
The voltage on pin IREF1, that is defined by the resistance of the NTC (together with the optionally used R6/R7),
must have the same voltage level as IREF2 at the corner temperature, where the down regulation starts to work.
So, the overall resistance of IREF1 is similar to the resistance on pin IREF2 at that corner temperature.
For a better illustration, an example is given below:
R IREF 2 = 47 kΩ
TStart = 85°C
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Author: SSZ
Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
V IREF 2 = I REF 2 ⋅ RIREF 2 = 50 µA ⋅ 47 kΩ = 2.35V
V IREF1 = 2.35V @ TStart → RIREF 1(T =85°C ) = 47 kΩ
NTC selection according to the corresponding NTC datasheet. A standard NTC (e.g. BC components, part no.
2322 640 55474) with a nominal value of:
R NTC (T = 25°C ) = 470kΩ was selected.
It has a resistance of:
R NTC (T =85°C ) = 36.05kΩ
at T=85°C .
To get the 47kΩ on IREF1 at T=85°C, a resistor of:
R IREF1 = R NTC (T =85°C ) + R 7
R 7 = R IREF1 − R NTC (T =85°C ) = 47 kΩ − 36.05kΩ
R 7 = 10.95kΩ
has to be added in series to the NTC.
With this selection, RNTC(T=25°C) = 470kΩ and R7= 10.95kΩ, the temperature regulation starts from Tamb= 85°C.
If the temperature increases further, the resistance of the NTC drops even more and lowers the voltage on IREF1.
This way, the current threshold level at RSENSE is lowered which results in a lower peak current and thus, a lower
average LED current. Less current through the LED(s) generate less heat which increases the NTCs resistance
again: the current threshold level at RSENSE is increased and as a consequence, the average LED current rises
again. Depending on the thermal design and the ambient temperatures of the module, the regulation works faster
or slower around the adjusted corner temperature point.
The following schematic shows the connection of an external temperature sensor to the EVB10803:
Figure 4: External NTC for temperature down regulation
390121080301
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Author: SSZ
Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
9.
Used Components
Board Part Type
Number
Category
Part Name
Alternative Part(s)
(Manufacturer) (Manufacturer)
Data Sheet Download
D1
Rectifier
Schottky
Diode
SS24
(FCH)
many
www.fairchildsemiconductor.com
D2
Rectifier
Ultrafast
Recovery
ES2D
(FCH)
many, e.g.
BYD77 (PHI)
www.fairchildsemiconductor.com
D3
Diode
Switching
Diode
MCL4148
many
www.vishay.com
T1
Switching
Transistor
n-channel
MOSFET
BSP318S
(INF)
many, e.g.
NTF3055 (ON)
www.infineon.com
L1
Inductor
Power
choke
WE-PD 100µH
(WE)
many, e.g.
www.wuerth-elektronik.de
MSS1260-104ML (CC)
C1
Capacitor
220nF/50V
Ceramics,
X7R, 1206
type
B37941
(EP)
many
www.epcos.com
C2
Capacitor
47µF/35V
Electrolytic,
low ESR
EEEFK1V470P
(PS)
many
www.panasonic.com/industrial
C3
Capacitor
100nF/50V
Ceramics,
X7R, 0805
type
B37941
(EP)
many
www.epcos.com
C4, C5, C6
Capacitor
Ceramics,
X7R, 0805
type
Not populated by default,
to be populated on demand by customer
R1, R2, R8,
R9, R10
Resistors
5% tolerance
0805 type
D12CRCW
(VS)
many
www.vishay.com
R3
Resistor
0.33Ω/0.5W
1% tolerance
1206 type
LR1206-R33Fl
(WW)
many
www.welwyn-tt.co.uk
R4
Potentiometer
500k/0.25W,
20% tolerance
TrimmingPotentiom.
Bourns 3314
many
www.bourns.com
R5
Potentiometer
100k/0.25W,
20% tolerance
TrimmingPotentiom.
Bourns 3314
many
www.bourns.com
R6, R7
Resistor
0805 type
Not populated by default,
to be populated on demand by customer
manufacturer codes:
FCH = Fairchild Semiconductor
WE = Würth Elektronik
INF = Infineon
YG = Yageo
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Author: SSZ
Rev. 5.01
PHI = Philips Semiconductor
VS = Vishay
CC = Coilcraft
WW = Welwyn
PS = Panasonic
ON = On Semiconductor
EP = Epcos
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Evaluation board EVB10803
Power LED driver for automotive applications
10.
EMI Measurement of the EVB10803
The EVB10803 is designed for a good electromagnetic emission behaviour. Please refer to the MLX10803 IC
specification as well as to the available application notes for general EMC considerations. The test was performed
on the original evaluation board and the settings shown below. No additional filter components had been used.
The conducted electromagnetic emission measurement was accomplished according to IEC 61967 part 4. The RF
was decoupled from line VBAT.
Settings EVB10803:
VBAT =13.5V
LED: Luxeon III @ ILED = 350mA
RIREF2 = 25kΩ
RROSC = 390kΩ
fsw(13.8V) = 34 kHz
Figure 6: Conducted electromagnetic emission EVB10803
390121080301
20/Mar/2006
Author: SSZ
Rev. 5.01
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Evaluation board EVB10803
Power LED driver for automotive applications
11.
Conclusion
The MLX10803 evaluation board was designed to provide an easy solution for demonstrating the use of high
brightness LEDs in conjunction with the MLX10803 LED driver chip. It is suitable to be driven under automotive
supply conditions (12V board systems) and is optimized in terms of electromagnetic emission behaviour
to be able to fulfill automotive standards.
If good emission behaviour is not an issue (e.g. industrial/consumer applications), smaller caps (for C1/C2) as
well as an unshielded coil can be used. Thus, size and cost can be reduced once more.
For the latest version of this document, go to our website at:
www.melexis.com
Or for additional information contact Melexis Direct:
Europe and Japan:
Phone: +32 13 61 16 31
E-mail: [email protected]
All other locations:
Phone: +1 603 223 2362
E-mail: [email protected]
QS9000, VDA6.1 and ISO14001 Certified
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Author: SSZ
Rev. 5.01
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