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APPLICATION INFORMATIONDESIGN CONSIDERATIONS IN SELECTION OF CONVERTERCONFIGURATION FOR AUTOMOTIVE LED HEADLIGHT
APPLICATIONS
By Vashist Bist and Shashank Wekhande, Systems Engineers
Allegro MicroSystems

ABSTRACTINTRODUCTION

This application note discusses LED headlights for twowheelers, passenger vehicles, commercial vehicles, andmild hybrid vehicles, and explores battery voltage andpower requirements for the headlights used in these vehicles. Detailed analyses are provided to help select a converter topology. A survey of buck, boost, and buck-boost
converter configurations is showcases advantages andlimitations when used in automotive headlight application.
Converter configurations with and without an LED capacitor
are highlighted, including design challenges, advantages,
and limitations of both configurations.

LEDs for automotive lighting application are becoming
increasingly popular for their low power consumption andsmaller form factor. These headlights are categorized basedon luminous intensity levels, which are typically governedby regulating authorities. Luminous intensity levels partiallydetermine the peak power requirement of a headlight.

Many diverse LED drivers and controllers offered by Allegro
MicroSystems cater to the requirements of automotive
headlight applications. These highly integrated ICs areoffered in small packages with numerous features forheadlight application as well as protection and diagnostics.
Requirements and key specifications of the Allegro offerings
are presented. Allegro devices for automotive headlightapplication are compared, with a focus on the specifications that are critical to the design and selection of converter
configurations that use these devices.
The Allegro devices presented in this application note support the design of converters in diffrent configurations andwith various power and voltage levels.

LEDs in headlights are fed by either a constant-current LED
driver or an LED controller, depending on the power level. In
low-power applications, LED drivers are referred to a device
with an integrated power stage. In high-power applications,an LED controller provides a gate driver with an external
power stage.
LED drivers and controllers are designed into various
converter configurations based on the voltage and power
requirement of the headlights. Three converter configurations are widely used in the LED headlight application—
buck, boost and buck-boost converter. Selecting fromthese converter topologies depends on the requirements ofnumerous input and output parameters such as the numberof LEDs (i.e., output voltage), battery voltage (input voltage), and LED current (i.e., output power). Other specificparameters such as the LED driver/controller maximum
specified voltages of various pins, board space, efficiency,
and thermal requirements also determine the selection of
the converter configuration.

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APPLICATION INFORMATIONHEADLIGHT CLASSIFICATION

Passenger Vehicle (PV) (12 V Battery)Headlights are classified based on the minimum and maximum luminous intensity in low-beam operation, as presented
in Table 1. The power requirement is calculated considering
an average of 100 lumens per watt of LED efficiency. Twowheeler headlights are generally Class B, whereas passenger
vehicles are generally Class C or Class D, although, somehigh-end luxury vehicles use Class E headlights.

Passenger vehicles implement a 12 V battery to drive theheadlights. The lumen/power requirement for passenger
vehicles generally is Class C or higher. Depending on thenumber of LEDs in the high-beam operation, buck-boost
or the boost controllers are used by numerous manufacturers. Because the power level is higher than two-wheelers, acontroller (gate driver plus control) with an external MOSFET
is generally used.

Table 1: Headlight Classification [1]NOTE: This table presents a typical comparison based on datacompiled from various regulations. Allegro does not guarantee theaccuracy of this table and recommends referring to country-specificguidelines for details.
Headlight
Class

LB Min.
(Lumens)

LB Max.
(Lumens)

LB Power(W)

Class A

150

900

~1.5 to 9

Class B

350

1000

~3.5 to 10

Class C

500

2000

~5 to 20

Class D

1000

2000

~10 to 20

Class E

>2000

–

> 20

[1] Considering typical ~100 lm/W LED efficiency, 100% optical
efficiency

HEADLIGHT POWER/VOLTAGE CLASSIFICATION

Commercial Vehicle (24 V Battery)
A few applications of commercial vehicles use a two-battery
arrangement, which increases the typical battery voltage to
24 V. The headlight category for such vehicles is Class C or
higher, which demands a device with support for higher voltage. For a 24 V battery, the requirement of the load-dump
voltage also increases from 40 V in a 12 V battery to 60 V,
which also limits the operation of the converter to certain
voltage/current levels.
In this category, both buck-boost and boost controller configurations can be implemented depending on the numberof LEDs.

Mild Hybrid (48 V Battery)Headlights can be classified in terms of the power and voltage requirements for different applications as follows.

In recent trends, mild hybrid passenger vehicles started using
48 V batteries. A 48 V battery has a 60 V load-dump voltage.
In such applications, only an input-voltage-referred buckconverter can be used to drive the headlight with a limited
number of series-connected LEDs.

Two-Wheeler (12 V Battery)

CONVERTER CONFIGURATIONClass B headlights are generally required for two-wheelers,
although some high-end two-wheelers require Class C or
Class D headlights.
For low-power (Class B) headlights, the brightness (lumen)requirement is met using only a small quantity of LEDs—generally, three LEDs in high-beam operation. For a 12 V battery
supply driving three LEDs, a buck converter can be used.
Because two-wheelrs have a low current requirement,
devices with integrated FETs are preferred for their ability torealize a smaller-size and lower-cost system.
A limited number of two-wheelers require Class D headlights. These applications use a buck-boost configuration.

This section describes the various configurations of converters used for LED headlight applications. The advantages
and disadvantages of various topologies are discussed andcompared.
The driver/controller IC is generally limited by:• Input voltage (Vin)• Output (LED) voltage (Vout)• Voltage on the LED sense resistor nodes (LP/LN)• Voltage on the switching node (i.e., switch voltage)• Minimum and maximum duty (Dmin and Dmax)• LED configuration (Vin-referred or GND-referred)• Thermal limitation
Various converter configurations are described next.

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Buck Converter
The advantage of an input-referred buck converter (as shownin Figure 1) is the use of a low-side switch that leads to simple
gate driver design. The LEDs are connected on the input
side as shown in Figure 1, and a buck converter controls thecathode voltage of the LEDs. The output voltage of the buckconverter is always lower than the input voltage, which limits
the number of LEDs at lower input voltage to small quantities.

mum number of LEDs in the boost converter is also limited by
the voltage rating of the LP/LN pins and the switching node
(SW pin) voltage, which is equal to the output voltage. This
voltage is typically 60 V, which limits the maximum quantityof LEDs to 20.
Similarly, the minimum and maximum quantity of LEDs for a
24 V battery can be designed based on the rating of the LP/
LN pins and SW pin.

For a 12 V battery application, the load dump voltage istypically approximately 40 V, which requires the driver/controller input voltage to be higher than 40 V. Considering
the minimum input voltage of 12 V, a maximum of three LEDs
can be driven because the voltage drop across these LEDs
is typically ~10 V. The operation of the buck is limited by the
maximum duty (Dmax) of the converter.
However, in a 48 V application, a maximum of 10 LEDs canbe driven with the typical output voltage of ~33 V. In this
scenario, buck converter operation is also limited by the
maximum duty at the lowest input voltage of 40 V, considering a voltage margin for the buck converter operation.
DSW
Cout
+

–
VLED

+
– Vin

LSW
SW

Figure 1: Buck converter configuration.

Boost Converter

Vin

DSW

LSW

Cout

SW
Vled

Figure 2: Boost converter configuration.

Buck-Boost/SEPIC Converter
The buck-boost converter is a very versatile configuration due
to the ability to buck and boost the voltage. A buck-boost
converter driven with a low-side switch is shown in Figure 3.
This allows wide flexibility in the number of LEDs in a design.
However, the voltage stress on the switch (i.e., voltage on
the switching node) is the sum of the input voltage and theoutput voltage and is the deciding factor in an LED driver/controller implementation.
To drive five LEDs, the output voltage requirement of theconverter is typically ~16.5 V. This leads to an overall voltage
stress of ~66.5 V (on the SW and LP/LN pins) at 40 V input
voltage (load dump) for a typical driver. If the voltage rating of
the driver is higher, the number of LEDs can be increased insimilar fold.

A boost converter configuration, which provides an output
voltage higher than the input voltage, is shown in Figure 2. In
this configuration, the minimum number of LEDs is limited by
the maximum output voltage.
Considering a 12 V battery application with load-dump
voltage of approximately 40 V, the converter is intended tooperate at this voltage. Because it is a boost converter, theminimum output voltage must be more than 40 V. Therefore,
the boost converter requires at least 15 LEDs for low-beam
operation, which corresponds to a typical output voltage of~50 V. This also provides enough margin for the boost converter minimum duty operation (Dmin). Moreover, the maxi-

+
–

Cout

Vin

Vout

Vled
LSW
Vin

+
–

DSW
SW

Vout

Figure 3: A buck-boost converter configuration.

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APPLICATION INFORMATIONCOMPARISON OF VARIOUS CONVERTERCONFIGURATIONS

60

Buck

Vo

Vo = DVin

Vo =

Boost

Buck-Boost

1V(1 – D) in

D
Vo =
V
(1 – D) inL

Vo (1 – D)
ΔI Lsw f sw

DVin
ΔI Lsw f sw

DVin
ΔI Lsw f sw

Co

ΔI Lsw
8 f sw ΔVo

DI o
ΔVo f sw

DI o
ΔVo f sw

Vsw

Vin

Vo

Vin + Vo

Isw

Io

I in

I sw = Iin + Io

Iswr

DI o

DIin

D(Iin + Io )

Iswa

DIo

DIin

D(Iin + Io )IDa

(1 – D) Io(1 – D) Iin(1 – D) (Iin + Io )

IL

Io

I in

I sw = Iin + Io

40

BB/
BB

Bo-Bo
(Ext.)
BBBo(Ext.)
12 V(Ext.)
24 V

BB/BB (Ext.)
12 V

30
20
10

Table 2: Comparison of Various Converter Configurations
Parameter

Bk/Bk (Ext.)
48 V

50Power (W)

Criteria for topology selection, summarized in Table 2,
include the output voltage (Vo), inductor (L), output capacitor (Co), peak switch node voltage stress (Vsw), peak switch
current stress (Isw), rms switch current (Iswr), average switch
current (Iswa), average free-wheeling diode current (IDa)(“diode” for nonsynchronous and “switch” for synchronous
configurations), and inductor current (IL) for three configurations of buck, boost, and buck-boost converters.

70

0

Bk/
Bk
(Int.)
12 V

BB/
BB(Int.)
12 V
5

3

8
12
15
Number of LEDs

25

EVALUATION OF CONFIGURATIONSWITH/WITHOUT OUTPUT CAPACITOR
This section presents a comparison of buck converter
configurations with and without an output capacitor. Various
aspects of the converter such as LED ripple current, cost,
power loss/efficiency, size, EMI consideration, stability, andPWM accuracy are considered using the example of a 48 V
buck configuration. Buck converter configurations are shownin Figure 5 and Figure 6, without and with output capacitor,
respectively.
DSW
VLED

+
V
– in

LSW
SW

Figure 5: Buck converter configuration without LED capacitor.

• Boost offers a better advantage in terms of the voltage at
the switch node, which allows use of the driver for a large
number of LEDs, but has limitations when driving fewer
quantities of LEDs.

DSW
Cout
+
VLED

• Buck-boost overcomes the limitations of the boost
converter. However, the voltage stress on the switchingnode is higher, which eventually limits the quantity of LEDs
that can be included in large numbers.
Therefore, a combination of buck-boost (low-beam) andboost (high-beam) is used to attain operation with wideranging LED quantities. The quantity of LEDs is mapped bypower requirements for the various converter configurationsin Figure 4.

20

Figure 4: Converter mapping of power vs. quantity of LEDs.

As presented in this section:• Because the buck converter cannot drive a large numberof LEDs, it is preferred for applications with few LEDs
where current can be high. Buck configurations are also
applicable to 48 V battery systems.

24 V

+
V
– in

LSW
SW

Figure 6: Buck converter configuration with LED capacitor.

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System specifications for design evaluation are:

I L1

• Supply voltage (Vin) = 48 V (typical), 40 to 56 V

2.07 A• Number of LEDs in high-beam operation = 6

2.02 A• LED current = 2 A (regulated)

1.97 A• LED dynamic resistance = ~1.9 Ω

1.92 A• Expected LED current ripple is <10% at 48 V
• Worst-case inductor ripple current is ~50% at 48 V

2.07 A

Evaluation parameters are discussed next.

2.02 ALED CURRENT AND VOLTAGE RIPPLE
For a buck configuration without capacitor, the inductor isconnected directly in series with LEDs. Therefore, inductor
current and LED current are the same. Moreover, the ripple
voltage across the LED is governed by the dynamic resistance of the series-connected LEDs. To achieve a lower LED
ripple current, i.e., <10%, a 220 µH inductor is considered.
Simulation results for the buck converter without a capacitor
are shown in Figure 7. As can be observed, the inductor current, IL1, and the LED current, ILED, are the same, with a rippleof 150 mA (~7.5%). The LED ripple voltage of ~280 mV isobserved considering the dynamic resistance on the order of~1.9 Ω (series-connected LEDs).

I LED

1.97 A
1.92 AV Vin – VVL1

21.84 V21.74 V
21.64 V21.54 V
0.96 ms

0.97 ms

0.98 ms

0.99 ms 1.00 ms

Figure 7: Simulation of buck converter without capacitor (L = 220 µH), with
48 V supply voltage.

The simulation results of the buck converter with a capacitor
across LEDs is shown in Figure 8. In this configuration, an
inductor of 33 µH is considered, and a small ceramic capacitor of 2.2 µF is added across the LEDs. Because the inductor
size is reduced more than six-fold, the inductor ripple current
increases in similar fold to ~1 A (50%). However, the capacitor across the LEDs acts as a filter and bypasses the inductor
current ripple such that current ripple in the LED is low. The
LED ripple current observed is ~100 mA (5% of LED current).
Moreover, the voltage ripple across the LED (LED capacitor)
is observed to be approximatley 150 mV, which is almost half
the value observed in the configuration without the capacitor.

I L1

2.6 A
2.2 A
1.8 A
1.4 A

I LED

2.05 A
2.02 A
1.99 A
1.96 AV Vin – VVL1

21.80 V
21.75 V21.70 V21.65 V21.60 V
0.96 ms

0.97 ms

0.98 ms

0.99 ms 1.00 ms

Figure 8: Simulation of buck converter with capacitor (L = 33 µH, C = 2.2 µF),
with 48 V supply voltage.

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Six configurations of buck converters (with and without acapacitor across the LEDs) are compared:

As can be observed, the LED voltage ripple for the buck converter with the 180 µH inductor, no capacitor, is very similar
to the buck converter with a 33 µH inductor, 1 µF capacitor.
Moreover, compared to other configurations, the voltage
ripple reduces significantly (less than ~170 mV) with a 2.2 µF
capacitor (with 33 µH or 47 µH inductor).

• 180 µH inductor, no capacitor• 220 µH inductor, no capacitor• 33 µH inductor, 1 µF LED capacitor• 33 µH inductor, 2.2 µF LED capacitor

0.5• 47 µH inductor, 1 µF LED capacitor• 47 µH inductor, 2.2 µF LED capacitor

180 µH
33 µH + 1 µF
47 µH + 1 µF

12

220 µH
33 µH + 2.2 µF
47 µH + 2.2 µF

0.35
0.3
0.25
0.2
0.15
0.1
0.05
0

10
LED Current Ripple (%)

220 µH
33 µH + 2.2 µF
47 µH + 2.2 µF

0.4
LED Voltage Ripple (V)The variation of LED current ripple (%) with supply voltage forall six converters is shown in Figure 9. All have LED current
ripple of less than 10% at the rated supply voltage of 48 V.
Moreover, the LED ripple current of the 180 µH inductor, nocapacitor configuration is very similar to the 33 µH inductor,
1 µF capacitor configuration. Increasing to a 47 µH inductor
significantly reduces inductor ripple to less than 5% using a
1 µF capacitor and to less than 2% using a 2.2 µF capacitor.
14

180 µH
33 µH + 1 µF
47 µH + 1 µF

0.45

40

42

44

46
48
50
Supply Voltage (V)

52

54

8

Figure 10: LED voltage ripple vs. supply voltage for different inductor andcapacitor combinations.

6Power Loss and Thermal Impact
At similar current ratings, higher-value inductors have higher
DC resistance (DCR). For example, the DCR of a 220 µH
inductor (2.3 A-rated current) is typically approximately
885 mΩ; however, for a similar current rating, 33 µH inductors are typically available with a DCR value of 100 mΩ.

4
2
0

56

40

42

44

46
48
50
Supply Voltage (V)

52

54

56

Figure 9: LED current ripple vs. supply voltage for different inductor andcapacitor combinations.

The variation of the LED ripple voltage with supply voltage forsix combinations of the buck converter is shown in Figure 10.

The eight-fold difference in DCR significantly impacts power
losses in the inductor. The power loss for a 2 A-rated current
for 33 µH is approximately 400 mW; whereas, for a 220 µH
inductor, this increases to 3.54 W. Such high power loss
impacts the overall efficiency of the converter system andincreases the overall temperature of the PCB. Power losses
in various inductors of similar current rating are compared in
Figure 11.

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Cost
Power Loss

0.6

2.5

0.4

2

0.3

1.5

0.2

Power Loss (W)Cost (USD)

3.5
3

0.5

1

0.1
0

Size (Area and Volume)4

220 µH 180 µH 100 µH 47 µH 33 µH 2.2 µF 1 µF

The size of the inductor increases with inductance. Therefore, a larger inductor requires larger PCB area, resulting in alarger-volume solution, which is problematic for space-constrained applications. Areas and volumes of inductors listed
in Table 3 are compared in Figure 12. As shown in the figure,the area and volume requirements of the 220 µH, 180 µH,
and 100 µH inductors (the higher inductive values) are very
high compared to the 47 µH and 33 µH inductors (the lower
inductive values). The PCB space requirement for the larger
inductors is almost 2.7 times that of the smaller inductors.
This size difference becomes a crucial criterion in the selection of a converter configuration.

0.5

1.8

0

1.6

The cost of the inductor is a significant portion of the overallsystem cost. For a buck converter without a capacitor, thecost of a 220 µH, 2.3 A inductor or a 180 µH, 2.6 A inductor
is approximately $0.647 (when purchased in quantities of
5,000). However, for a buck converter with capacitor, use ofa 33 µH, 2.3 A inductor or a 47 µH, 2 A inductor significantly
reduces cost to $0.28 (when purchased in quantities of
5,000). Ceramic capacitors are significantly less expensive,with a typical cost of approximately $0.033 for a 2.2 µF, 50 V
ceramic capacitor to approximately $0.019 for a 1 µF, 50 V
ceramic capacitor. This brings the overall cost of the inductor (47 µH) and capacitor (2.2 µF) to $0.313—approximately
half the cost of a 180 µH/220 µH inductor. Details of various
inductors used for evaluation are provided in Table 3. The
costs of various 2 A inductors and 50 V ceramic capacitors
are compared in Figure 11.
Table 3: Comparison of Various Inductors
Value ( µH)

Current (A)DCR (mΩ)Company

Cost (USD)

220 µH

2.3

885

2.6

735

Pulse
Electronics

0.647

180 µH100 µH

2.1

150

Bourns

0.613

47 µH

2

135

33 µH

2.3

100

Eaton

0.647
0.28
0.28

Area (sq-cm)

System Cost

1.4
1.2

1.4

Inductor (~2 A)/Capacitor (50 V)
Figure 11: Cost and power loss of various inductors and capacitors.

Area
Volume

1

1.2
1

0.8

0.8

0.6

0.6

Volume (cu-cm)

0.7

0.4

0.4
0.2

0.2
0

220 µH 180 µH 100 µH

47 µH

33 µH

0

Inductor (~2A)
Figure 12: Area and volume requirements of various inductors.

Electromagnetic Interference (EMI)In headlight applications, the converter portion of theheadlight LED design is generally placed on a separate
PCB and connected via long cables. These cables act as anantenna, which increases the overall radiated emission of theboard. These emissions are directly proportional to the di/dt
and dv/dt on the cables, which can be related to the voltage
and current ripple on the LEDs. As discussed earlier, use ofa capacitor connected across the LEDs significantly reduces
the current and voltage ripple in the converter. Therefore,
EMI-related issues are comparatively less in capacitor-based
converters. Moreover, some smaller capacitors can also
be connected to filter-out noise at a specified frequency ofinterest.

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APPLICATION INFORMATIONThe buck converter without an output capacitor provides a
direct load-to-inductor connection. Therefore, current control in the inductor (or load) can be performed simply using ahysteresis (bang-bang) controller, which gives an advantage
of easy implementation. Moreover, because the LED capacitor is not present, the buck converter is realized as a singlepole system where the crossover frequency and bandwidth
are high, thus making the converter inherently stable.

LED capacitor, where the output capacitor demands extra
current. Moreover, to limit the peak current, many devices
use a soft-start feature, which further reduces the current
charging slope. This worsens the overall PWM accuracy, andcompensation must be made by the driver/controller. Buckconverters designed with and without an LED capacitor arecompared in Table 4.
Table 4: Comparison of Buck Converter Configurations With andWithout LED Capacitor

For a buck converter with an output LED capacitor, the overallsystem response is of the second order (pole and zero). The
current control implementation generally employs a peakcurrent control mode with added slope compensation forhandling subharmonic issues at higher duty. To realize astable system over the required load/voltage specifications,the compensation loop must be tuned properly. This tuning
for system stability can be achieved with long- and widelyused loop-compensation techniques.

Parameters

Without Capacitor(High Inductance)

With Capacitor(Low Inductance)

Inductor Current Ripple

Low

High

LED Current Ripple

MediumLow

LED Voltage Ripple

MediumLow (High Cap.)

Power Loss

High

Low

PWM Accuracy

Charging and discharging have finite slopes that are dependent on input voltage (Vin), output voltage (Vo), and inductor
value (L). The charging slope is different than the discharging slope, as shown in Figure 13. As a result, PWM accuracy(applied duty vs. actual duty) varies slightly and external
compensation must be made.

IL

Low

Size (Area /Volume)

Very HighLow

EMI Issues

High

Low

Converter Stability

Minimal Tuning

Need Tuning

PWM Accuracy

BetterNominalAllegro offers a wide range of devices that cater to different
automotive headlight applications. Different Allegro devices
for a variety of applications are compared in Figure 14 basedon power vs. supply voltage. Details of the device offerings
are presented next.
A80803(BB-BB / B-B)

A80803(BK-BK)

A80803(B-B/ B-BB / BB-BB)

Power (W)50 W

A6271-HV
(B-B)

Vo
L

A6271-HV(BB-BB)
A6271-Std.
(BB-BB)
Int. MOS

ALT80802(BB-BB)

Ext. MOS

A6213/17(BK)

15 W 20 W

Vin – VoL

Lower HeatingHigh

ALLEGRO PORTFOLIO FOR AUTOMOTIVEHEADLIGHT APPLICATION

Expected Average
Δi L

Higher Heating

70 W

PWM dimming is a commonly used feature in automotive
LED applications. In a buck converter without an LED capacitor, the inductor current and the load current are the same.
Also, because an LED capacitor is not present, the peakcurrent requirement for capacitor charging is eliminated. As aresult, inductor (load) current quickly rises to the peak value,
at which point the device enters current-limiting operation.

Thermals
System Cost

30 W

Stability

Achieved Average

Figure 13: PWM accuracy in current-controlled converters.

ALT80800/02,
A6214/16 (BK)
A6213-1/17-1/
APM80900/04 (BK)

12 V

18 V

24 V

48 V

Supply Voltage (V)The need to compensate for variation in PWM accuracy isprominent in the case of a buck converter with an output

Figure 14: Power and voltage map showcasing various Allegro devices forheadlight application.

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Two-Wheeler Application

Truck Application

Two-wheelers require a small quantity of LEDs poweredby a 12 V battery. The preferred device for this application
typically has an integrated MOSFET. This minimizes size andcost. Allegro devices for this application include:

The battery voltage requirement for trucks is 24 V. Thisapplication also requires a greater quantity of LEDs (>10) for
headlights. Therefore, controller ICs such as the A80803 aresuited for this application.

• ILED < 1.5 A: A6213-1, A6217-1, APM80904

Mild-Hybrid Application• ILED < 2 A: A6214, A6216, ALT80802, ALT80800 (Synch. Buck)

This application requires power from a 48 V battery and support for a 60 V load dump. Thus, this application requires aninput-voltage-referred buck controller. The Allegro A80803
device is recommended for driving this configuration.

• ILED < 3 A: A6213, A6217, A6271-1 (Gate Driver)Four-Wheeler (Passenger Vehicle) Application
Passenger vehicles require a greater number of LEDs powered by a 12 V battery. The preferred device for this application is therefore typically a controller IC (i.e., gate driver plus
control). Allegro devices for this application include:

Key headlight specifications and recommended Allegro
devices are summarized in Table 5. Key specifications of various Allegro devices are compared in Table 6.

• A6217-1 (Standard Configuration)• A6271-1 (High-Voltage Configuration)• A80803 (Multi-Topology Configuration)
Table 5: Key Headlight Specifications and Recommended Allegro Devices
S.No.

HB LED(Nos.)

LB LED(Nos.)

Vbat/Load
Dump (V)LED Current(A)

LED Power(W)

Vehicle Type

Headlight
Class

Slew Control

Allegro IC

1

3

2

12 to 18 V, 40 V

< 1.5 A

~15 W

2-wheeler

A-B

Buck

Buck

Inherent (No o/p Cap.)

A6213-1/17-1

2

3

2

12 to 18 V, 40 V

< 1.5 A

~15 W

2-wheeler

A-B

Buck

Buck

External (with o/p Cap.)

A6213-1/17-1

3

3

2

12 to 18 V, 40 V

< 1.5 A

~15 W

2-wheeler

A-B

Buck

Buck

External

APM80900/04

4

3

2

12 to 18 V, 40 V

<2 A

~20 W

2-wheeler

B-D

Buck

Buck

External

ALT80800/02,
A6214/16

5

3

2

12 to 18 V, 40 V

<3 A

~30 W

2-wheeler

B-D

Buck

Buck

Inherent (No o/p Cap.)

A6213/17

6

3

2

12 to 18 V, 40 V

<3 A

~30 W

2-wheeler

B-D

Buck

Buck

External (with o/p Cap.)

A6213/17

7

3-5

2-3

8 to 18 V, 40 V

<2A

~30 W

2-wheeler

B-D

Buck-Boost

Buck-Boost

External

ALT80802Topology (HB) Topology (LB)

8

≤5

≤5

8 to 18 V, 40 V

<2A

~30 W

2-wheeler

B-D

Buck-Boost

Buck-Boost

External

A6271-1 (Std.)

9

≤ 12

≤ 12

8 to 18 V, 40 V

< 1.2 A

~50 W

4-wheeler≥C

Buck-Boost

Buck-Boost

External

A6271-1 (HV)

10

≤ 20

≥ 15

12 to 18 V, 40 V

< 0.8A~50 W

4-wheeler

≥C

Boost

Boost

External

A6271-1 (HV)

11

≤ 20

≥ 15

12 to 18 V, 40 V

< 0.8A~50 W

4-wheeler

≥C

Boost

Boost

Integrated

A80803

12

≤ 20

1-11

12 to 18 V, 40 V

< 0.8A~50 W

4-wheeler

≥C

Boost

Buck-Boost

Integrated

A8080313

1 to 11≤ 11

12 to 18 V, 40 V

< 1.5 A

~50 W

4-wheeler≥C

Buck-Boost

Buck-Boost

Integrated

A80803148

5

16 to 36 V, 60 V

< 2.8A~70 W

Trucks≥C

Buck-Boost

Buck-Boost

Integrated

A8080315≥ 20-25≥ 15

16 to 36 V, 60 V

< 0.8A~70 W

Trucks

≥C

Boost

Boost

Integrated

A80803

16

10

<10

40 to 56 V, 60 V

<2A

~70 W

4-wheeler (MH)

≥C

Buck

Buck

Integrated

A80803

Table 6: Key Specification Comparison of Various Allegro ICs
Parameter

A6213

A6213-1

A6214/16

A6217

A6217-1

ALT80800

ALT80802

APM80904

A6271-1Topology

N.Sy. Buck

N.Sy. Buck

N.Sy. Buck

N.Sy. Buck

N.Sy. Buck

Sy. Buck

NS Buck/BB

Sy. Buck

Multi

A80803
Multi

Int. MOS/Gate DriverInt. MOS

Int. MOS

Int. MOS

Int. MOS

Int. MOS

Int. MOS

Int. MOS

Int. MOS.

Gate Drv.

Gate Drv.
No

Int. Inductor

No

No

No

No

No

No

No

Yes

No

Iout

3A

1.5 A

2A

3A

1.5 A

2A

2A

1.5 A

–

–

Vin

6 to 48 V

6 to 48 V

4.5 to 55 V

6 to 48 V

6 to 48 V

4.5 to 55 V

3.8 to 50 V

4.5 to 36 V

4.2 to 50 V

5 to 37 V

SW

50 V

50 V

60 V

50 V

50 V

60 V

55 V

40 V

–

80 V

CS Node

–

–

60 V

7V

7V

60 V

55 V

40 V

58 V

80 V

LED Cap.

No

No

Yes

No

No

Yes

Yes

Yes

Yes

Yes

Slew Control

No

No

No

No

No

No

No

No

No

Yes

955 PERIMETER ROAD • MANCHESTER, NH 03103 • USA+1-603-626-2300 • FAX: +1-603-641-5336 • ALLEGROMICRO.COM

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AN296281
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APPLICATION INFORMATIONCONCLUSIONREFERENCES

To help designers find the appropriate device for specificautomotive headlight applications, the automotive headlightapplication has been overviewed. Requirements of headlights for two-wheelers, passenger vehicles, commercial
vehicles, and mild hybrid vehicles have been presented.
Limitations and applicability of various topologies—such as
the buck, boost and the buck-boost converter—have beenreviewed. Comparisons of converter configurations withand without an output LED capacitor have been consideredbased on inductor and LED current ripple, LED voltage
ripple, system cost, power loss (efficiency), thermals, solution
size, EMI, stability, and PWM accuracy.

[1] A6213 and A6213-1, Automotive-Grade, Constant-Current PWM Dimmable Buck Regulator LED Driver, Allegro
Microsystems, June 2021. https://www.allegromicro.
com/en/products/regulate/led-drivers/led-drivers-forlighting/a6213

Several Allegro offering have also been presented for a wide
range of products in LED drivers and controllers. The Allegro
devices support numerous converter design configurations
and are offered with integrated protection and diagnostics.
With a high level of integration and a wide range of productselection, the Allegro devices give the user optimal design
flexibility.

[2] A6217 and A6217-1, Automotive-Grade, Constant-Current PWM Dimmable Buck Regulator LED Driver, Allegro
Microsystems, June 2020. https://www.allegromicro.
com/en/products/regulate/led-drivers/led-drivers-forlighting/a6217[3] APM80904, Automotive-Grade, Low-EMI, 1.5 A PWM
Dimmable Synchronous Buck LED Module, Allegro
Microsystems, March 2021. https://www.allegromicro.
com/en/products/regulate/clearpower-modules/leddriver-modules/apm80900-apm80904[4] A6214 and A6216, Automotive-Grade, Constant-Current
2 A PWM Dimmable Buck Regulator LED Driver, Allegro
Microsystems, March 2022. https://www.allegromicro.
com/en/products/regulate/led-drivers/led-drivers-forlighting/a6214-a6216[5] ALT80800, Automotive-Grade, Constant-Current 2.0 A
PWM Dimmable Synchronous Buck LED Driver, Allegro
Microsystems, November 2021. https://www.allegromicro.com/en/products/regulate/led-drivers/led-driversfor-lighting/alt80800[6] ALT80802, Wide Input Voltage, Adjustable Frequency,
Buck-Boost or Buck 2 Amp LED Driver, Allegro Microsystems, September 2019. https://www.allegromicro.
com/en/products/regulate/led-drivers/led-drivers-forlighting/alt80802[7] A6271-1, Automotive High-Current LED Controller,
Allegro Microsystems, July 2019. https://www.allegromicro.com/en/products/regulate/led-drivers/led-driversfor-lighting/a6271-1[8] A80803, Multi-Topology LED Driver with PWM Dimmingand Seamless High/Low Intensity Modes, Allegro Microsystems, June 2021. https://www.allegromicro.com/en/
products/regulate/led-drivers/led-drivers-for-lighting/a80803955 PERIMETER ROAD • MANCHESTER, NH 03103 • USA+1-603-626-2300 • FAX: +1-603-641-5336 • ALLEGROMICRO.COM

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AN296281
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APPLICATION INFORMATION

Revision History
NumberDate

Description

Responsibility–

March 9, 2023

Initial release

V. Bist, S. Wekhande

Copyright 2023, Allegro MicroSystems.

The information contained in this document does not constitute any representation, warranty, assurance, guaranty, or inducement by Allegro to the customer with respect to the subject matter of this document. The information being provided does
not guarantee that a process based on this information will be reliable, or that Allegro has explored all of the possible failuremodes. It is the customer’s responsibility to do sufficient qualification testing of the final product to ensure that it is reliable andmeets all design requirements.
Copies of this document are considered uncontrolled documents.

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