AND8220-D [ONSEMI]
Automotive Applications The Use of Discrete; 汽车应用离散的应用
| 型号： | AND8220-D |
| 厂家： | 
ONSEMI |
| 描述： | Automotive Applications The Use of Discrete |
| 文件： | 总6页 (文件大小：237K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AND8349/D
Automotive Applications
The Use of Discrete
Constant Current
Regulators (CCR) For
CHMSL Lighting
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APPLICATION NOTE
Prepared by: Brian Blackburn (FAE),
Mike Sweador (AE)
ON Semiconductor
LEDs are being proliferated into many automotive
lighting applications. The Center High Mount Stop Lamp
(CHMSL) is one of several automotive applications for
LEDs. Interior lighting is another area where LEDs are very
well suited due to their small size and high efficiency. Recent
advancements in higher efficiency LEDs at lower costs have
made these light sources the technology of choice for
automotive lighting.
Since LED brightness is determined by operating current,
optimum intensity may require a constant current approach
to maintain consistent luminosity over the wide variation of
battery voltage possible in automotive electrical systems.
Battery voltage typically is 13.5 V; however, it can range
from as low or less than 9 V in a faulty charging system to
24 V for several minutes in a double battery jump scenario.
shown to have several distinct advantages for controlling the
LED operating current compared to the common method of
selecting a bias resistor to adjust the LED operating current.
Figure 1 shows a typical I-V curve for the NSI45030T1G
device. The CCR is a current regulator that offers
outstanding regulation for LEDs and other applications
requiring a low cost, stable current source. Unlike costly
switching regulators, a CCR is relatively EMI free, does not
require startup circuitry, and operates as a current source or
sink. Current regulation can be achieved for
Anode−Cathode voltages ranging from as little as 1.8 V. No
external components are required to regulate the typical
value of 30 mA. Since these are CCR sources, parallel
arrangements allow for higher load current applications.
(Figure 7)
The CCR reduces the complexity of resistor biased
designs for sensitive loads such as LED strings connected in
series (Figure 4). Simply apply a voltage greater than
The list of potential automotive lighting LED applications
includes:
• CHMSL Arrays
• Instrument Cluster Backlighting
• Switch Cluster Backlighting and Tell−Tales (Icon
Lighting)
V
to achieve an accurate regulated current.
overhead
80
70
• Dome Lighting
60
• Mirror Lights
50
40
• Fog Lights
30
• Convenience Lighting
• RGB Ambient Lighting
20
10
• Emergency Flashlight
0
Each application requires specific attention to light output
and optical design, LED circuit topology, driver current
requirements, and thermal management. It is the intent of
this article to concentrate on CHMSL LED circuit
requirements, and to discuss thermal management as it
applies to the driver circuitry.
−10
−20
−30
−10
0
10
20
30
40
50
V
AK
, ANODE−CATHODE (V)
Figure 1. CCR IV Characteristics
An innovative use of a new Patent Pending Discrete
Technology (Constant Current Regulator – CCR) will be
© Semiconductor Components Industries, LLC, 2009
1
Publication Order Number:
May, 2009 − Rev. 1
AND8349/D
AND8349/D
A CCR is a nearly ideal current source providing constant
LED and protects the CCR from conducting in the reverse
bias mode (Figure 1).
current regardless of applied voltage above its operating
minimum. In simple terms, a CCR can be considered a
nonlinear voltage controlled resistor.
A basic CHMSL configuration with 3 Red LEDs in series
is shown in Figure 4. A CCR provides a uniform intensity
over full line voltage swings and greatly reduces LED power
dissipation as compared to common resistor biasing. At 9 V
battery input, a CCR provides a higher current than a typical
biasing resistor value would provide (Figure 3). At 16 V a
stable, constant current is supplied by the CCR.
The Power Dissipation (P ) in an LED is P = I V. Since
d
d
the CCR acts as a voltage controlled resistor while the
resistor biasing fixes the resistor value, the LED Power
dissipation is shown to be nearly constant over a variable
battery range. (Figure 3)
For automotive CHMSLs, a constant current source for
LEDs reduces stress conditions caused by overdriving with
current as compared to resistor biasing. A Reverse
protection diode (MBRS140T3 in Figure 4) prevents a
reverse voltage condition which can permanently damage an
Figure 2 shows a comparison of CCR vs. Resistor Bias
current over battery voltage variation from 9 V to 16 V. The
LED current, and therefore intensity, is constant with the
CCR device compared to the resistor bias.
240
40
T = 25°C
T = 25°C
A
A
220
35
Circuit Current with
LED Power with
200
CCR Device
30
CCR Device
180
160
140
25
Circuit Current
with 250 W
LED Power
120
20
with 250 W
Representative Test Data
for Figure 6 Circuit, Current
of LEDs, FR−4 @ 300 mm ,
Representative Test Data
for Figure 6 Circuit, Pd of
100
80
15
2
2
LEDs, FR−4 @ 300 mm ,
1 oz Copper Area
13 14
(V)
1 oz Copper Area
10
60
9
10
11
12
15
16
9
10
11
12
13
(V)
14
15
16
V
V
in
in
Figure 2. Series Circuit Current
Figure 3. LED Power
MBRS140T3
CCR
CCR
CCR
CCR
CCR
Figure 4.
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2
AND8349/D
D8
R1
D1
Anode
205
Q1
Q2
Qx
MBRS140T3G
HF3−R5570
D5
Cathode
V
SUPPLY
13.5Vdc
HF3−R5570
LED
LED
LED
D6
+
V
in
−
HF3−R5570
HF3−R5570
HF3−R5570
HF3−R5570
LED
LED
LED
D7
HF3−R5570
HF3−R5570
HF3−R5570
LED
LED
LED
0
HF3−R5570
HF3−R5570
HF3−R5570
Figure 5.
Figure 5 shows a typical resistive bias for a single
CHMSL LED string. The resistor value is calculated to take
Figure 6. Typical Application Circuit
(30 mA each LED String)
into account the V
across the series connected LED
fwd
string. If a specific supply voltage, such as 13.5 V, is used,
a specific resistor can be chosen to supply a 30 mA drive
current.
Number of LED’s that can be connected is determined by:
D1 is a reverse battery protection diode
LED’s = (V − (Q V + D1 V )) / LED V
in
X
F
F
F
Example for a 3 Red LED String:
Example: V = 12 Vdc, Q V = 3.5 Vdc, D1VF = 0.7 V
in
X
F
V
supply
V
sw_bat
V
supply
–V
= 0 V
= 13.5 V Typical
– V – (I_ R ) – (3 V ) = 0 V
sw_bat
rpd
led
1
fwd
LED V = 2.2 Vdc @ 30 mA
F
(12 Vdc − 4.2 Vdc)/2.2 Vdc = 3 LEDs in series.
V
= 0.8 V
= 2.20 V
rpd
For application versatility, if more Current drive is
required, the CCRs can be connected in parallel to boost the
regulated current.
V
fwd
I_ = 30 mA
led
13.5 V * 0.8 V * 3(2.20 V)
R1 +
30 mA
D1
(eq. 1)
+ 203 W or205 W (Standard 1% Value).
Q1
Q2
Qx
Anode
This method for setting the current with a specific resistor
is well known. By knowing the LEDs worst case V , and
fwd
Cathode
the light intensity required, a specific range of resistor values
can be chosen. However, as the supply voltage varies from
9 V to 16 V, the current changes in the LED which affects the
intensity. With the same 205 W resistor and 9 V supply,
+
V
in
LED
−
HF3−R5570
rearranging the equation and solving for I_ yields 7.8 mA.
Assuming all of the parameters remain constant and the
led
LED
HF3−R5570
supply voltage is elevated to 16 V, an I_ value of 42 mA
led
is calculated. Again, the intensity of the LED is affected.
A CCR from ON Semiconductor would keep the current
and intensity constant over this supply voltage range
(Figure 2).
LED
HF3−R5570
Here is how you can use ON Semiconductor’s CCR to
determine how many series LEDs it can drive.
Figure 7. Typical Application Circuit
(90 mA each LED String)
Number of LED’s that can be connected is determined by:
D1 is a reverse battery protection diode
Example: V = 12 Vdc, Q V = 3.5 Vdc, D1VF = 0.7 V
in
X
F
LED V = 2.6 Vdc @ 90 mA
F
(12 Vdc − (3.5 + 0.7 Vdc))/2.6 Vdc = 3 LEDs in series.
Number of Drivers = LED current/30 mA
90 mA/30 mA = 3 Drivers (Q1, Q2, Q3)
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3
AND8349/D
MBRS140T3G
(Reverse Protection Diode)
Bias Resistor
(250 W)
Vbat (+)
Jumper(s) selects DUT
NSI45030T1G
(CCR)
V
LED
Test Point
NSI45030T1G
(CCR)
Vbat (-)
Jumper(s) to add/remove
LED from circuit
HF3-R5570
(3 red LEDs)
Figure 8.
CCR Demo Board
a slight negative trend as the power dissipation increases.
This negative trend reduces the power dissipation in the
CCR compared to the increasing power dissipation for a bias
resistor (Figure 9) and helps to prevent thermal runaway.
Since reduction in current is small, the change in LED
intensity is minimal.
Figure 11 shows thermal estimates for the NSI45030T1G
device with various heatsink footprints. If the heatsink area
is increased, the ambient operating temperature may be
increased. It is up to the circuit designer to understand the
thermal environment of the application and allow for device
This demo board (Figure 8) is the circuit shown in
Figure 6. It is used to generate several curves and can be used
to validate the CCR operation.
Figure 9 shows a comparison of power dissipation in a
CCR vs. Power dissipation in a Bias Resistor over battery
voltage variation from 9 V to 16 V. The CCR Power is less
than a Bias Resistor at higher operating voltages. At higher
Battery voltage, a higher wattage Power resistor would be
required increasing the circuit cost.
Figure 10 shows a typical Current / Voltage curve for a
CCR device. ON Semiconductor’s CCR is designed to have
400
thermals as specified in the device data sheet.
35
350
300
250
200
30
25
20
15
10
P CCR (mW)
d
150
100
50
P Resistor (mW)
d
0
9
10
11
12
13
(V)
14
15
16
0
1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10
, ANODE−CATHODE (V)
V
V
AK
in
Figure 9. CCR Pd vs. Resistor Pd
Figure 10. CCR−IV Characteristics @ 255C
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4
AND8349/D
THERMAL ESTIMATES FOR THE SOD-123 CCR DEVICE
800
700
600
500
400
300
200
100
PD max @ 855C
2
500 mm 2 oz
2
500 mm 2 oz Cu
241 mW
228 mW
189 mW
182 mW
117 mW
108 mW
2
2
500 mm 1 oz
500 mm 1 oz Cu
2
2
300 mm 2 oz Cu
300 mm 2 oz
2
2
300 mm 1 oz Cu
300 mm 1 oz
2
100 mm 2 oz Cu
2
100 mm 2 oz
2
100 mm 1 oz Cu
2
100 mm 1 oz
−40
−20
0
20
40
60
80
T , AMBIENT TEMPERATURE (°C)
A
Figure 11. Power Dissipation vs. Ambient
Temperature @ TJ = 1505C for Variable Copper
Heat Spreader
Summary:
Simple, Economical and Robust (SER), the solid state
CCR will allow the user to achieve the expected long life of
their LED array.
CCRs will improve the efficiency and extend the life of
CHMSL LEDs. They will minimize design time and speed
up time to market.
Since LED brightness is determined by operating current,
optimum intensity will be attained by using a CCR approach
to maintain consistent luminosity over the wide variation of
battery voltage in automotive electrical systems.
SOT−223 package devices are also available which
improve power dissipation. See application note
AND8391/D for a through thermal discussion for both the
SOD−123 and SOT−223 packages.
Eliminating the large range of resistor values that must be
uniquely chosen to compensate for the LED’s variation in its
V
fwd
is the best benefit to CCR LED biasing.
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5
AND8349/D
APPENDIX A
SOD−123 devices are:
SOT−223 devices are:
NSI45020T1G, Steady State I
NSI45025T1G, Steady State I
NSI45030T1G, Steady State I
NSI45020AT1G, Steady State I
NSI45025AT1G, Steady State I
NSI45030AT1G, Steady State I
= 20 mA $15%
= 25 mA $15%
= 30 mA $15%
= 20 mA $10%
NSI45025ZT1G, Steady State I
NSI45030ZT1G, Steady State I
NSI45025AZT1G, Steady State I
NSI45030AZT1G, Steady State I
= 25 mA $15%
= 30 mA $15%
= 25 mA $10%
reg(SS)
reg(SS)
reg(SS)
reg(SS)
reg(SS)
reg(SS)
reg(SS)
= 30 mA $10%
reg(SS)
= 25 mA $10%
reg(SS)
reg(SS)
= 30 mA $10%
APPENDIX B
Application Note
Title
AND8391/D
Thermal Considerations for the ON Semiconductor Family of Discrete Constant Current Regulators
(CCR) for Drivings LEDs in Automotive Applications
AND8220/D
AND8222/D
AND8223/D
How To Use Thermal Data Found in Data Sheets
Predicting the Effect of Circuit Boards on Semiconductor Package Thermal Performance
Predicting Thermal Runaway
The products described herein (NSI45030T1G) has patents pending.
ON Semiconductor and
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