NOTE: For detailed information on purchasing options, contact your
local Allegro field applications engineer or sales representative.
Allegro MicroSystems reserves the right to make, from time to time, revisions to the anticipated product life cycle plan for a
product to accommodate changes in production capabilities, alternative product availabilities, or market demand. The infor-
mation included herein is believed to be accurate and reliable. However, Allegro MicroSystems assumes no responsibility for
its use; nor for any infringements of patents or other rights of third parties which may result from its use.
Recommended Substitutions:
For existing customer transition, and for new customers or new appli-
cations, refer to the A6261KLJTR-T, A6262KLPTR-T, A6262KLYTR-T.
Automotive LED Array Driver
A6269
Date of status change: July 1, 2019
Deadline for receipt of LAST TIME BUY orders: December 27, 2019
These parts are in production but have been determined to be
LAST TIME BUY. This classification indicates that the product is
obsolete and notice has been given. Sale of this device is currently
restricted to existing customer applications. The device should not be
purchased for new design applications because of obsolescence in the
near future. Samples are no longer available.
Last Time Buy
Description
The A6269 is a linear, programmable current regulator providing
up to 200 mA from each of two outputs to drive arrays of high
brightness LEDs. The regulated LED current from each output,
accurate to 5%, is set by a single reference resistor. Current
matching in each string is better than 10% without the use of
ballast resistors. Driving LEDs with constant current ensures
safe operation with maximum possible light output.
Output control is provided by an enable input, giving direct
control for PWM applications, and by a debounced switch
input, proving an on/off toggle action.
Optimum performance is achieved driving 1 to 3 LEDs in
each string: up to 2 strings at 200 mA each. Outputs can be
connected in parallel or left unused as required.
Short detection is provided to protect the LEDs and the A6269
during a short-to-ground at any LED output pin. The output
will automatically resume the regulated current when the short
is removed.
A temperature monitor is included to reduce the LED drive
current if the chip temperature exceeds an adjustable thermal
threshold.
The device package is an 8-pin SOICN (LJ) with exposed pad
for enhanced thermal dissipation. It is lead (Pb) free, with 100%
matte tin leadframe plating.
A6269-DS, Rev. 10
MCO-0000581
Features and Benefits
▪AEC-Q100qualified
▪TotalLEDdrivecurrentupto400mA
▪Currentsharedequallyupto200mAby2strings
▪6to50Vsupply
▪Lowdropoutvoltage
▪LEDoutputshort-to-groundandthermalprotection
▪On/offtoggleswitchinput
▪EnableinputforPWMcontrol
▪CurrentslewratelimitduringPWM
▪Currentsetbyreferenceresistor
▪Automotivetemperaturerange
Applications:
Typical Application Diagram
A6269
Automotive LED Array Driver
▪Domelight,maplight,spacelighting,moodlighting
+
–
LA1
VIN
Automotive
12 V power net
GND
PAD
LA2
SW
On/Off
200 mA
200 mA
IREF
THTH
A6269
PWM dimming
input from LCU EN
Package: 8-pin SOICN with exposed
thermal pad (suffix LJ)
Not to scale
July 1, 2019
Automotive LED Array Driver
A6269
2
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Absolute Maximum Ratings1
Characteristic Symbol Notes Rating Unit
Load Supply Voltage VIN –0.3 to 50 V
Pin EN –0.3 to 50 V
Pins LA1, LA2 –0.3 to 50 V
Pins IREF, THTH, SW –0.3 to 6.5 V
Ambient Operating Temperature
Range2TAK temperature range –40 to 125 °C
Maximum Continuous Junction
Temperature TJ(max) 150 °C
Transient Junction Temperature TtJ
Over temperature event not exceeding 10 s, lifetime duration
not exceeding 10 h, guaranteed by design characterization 175 °C
Storage Temperature Range Tstg –55 to 150 °C
1With respect to GND.
2Limited by power dissipation.
Selection Guide
Part Number LED Outputs Ambient Operating
Temperature, TA (°C) Packing Package
A6269KLJTR-T 2 at 200 mA each –40 to 125 3000 pieces per 13-in. reel 8-pin SOICN with exposed thermal pad,
3.9 × 4.9 mm case
Thermal Characteristics*may require derating at maximum conditions, see application section for optimization
Characteristic Symbol Test Conditions* Value Unit
Package Thermal Resistance
(Junction to Ambient) RθJA
On 4-layer PCB based on JEDEC standard 35 ºC/W
On 2-layer generic test PCB with 0.8 in.2 of copper area each side 62 ºC/W
Package Thermal Resistance
(Junction to Pad) RθJP 2 ºC/W
*Additional thermal information available on the Allegro™ website.
Automotive LED Array Driver
A6269
3
Allegro MicroSystems
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www.allegromicro.com
LA1
VIN
VBAT
Current
Regulators
GND
PAD
Temp
Comp
Temp
Monitor
Slew
Limit
Current
Reference
Control
Logic
LA2
EN
SW
IREF
RREF
RTH
THTH
Deglitch
Power-On
Reset
D Q
C Q
R
Functional Block Diagram
Pin-out Diagram
LJ Package
8
7
6
5
1
2
3
4
SW
EN
VIN
LA2
THTH
IREF
GND
LA1
PAD
Terminal List Table
Number Name Function
1 THTH Thermal threshold
2 IREF Current reference
3 GND Ground reference
4 LA1 LED anode (+) connection 1
5 LA2 LED anode (+) connection 2
6 VIN Supply
7 EN Enable
8 SW Switch input
–PAD Exposed thermal pad
Automotive LED Array Driver
A6269
4
Allegro MicroSystems
955 Perimeter Road
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Supply and Reference
VIN Functional Operating Range26 – 50 V
VIN Quiescent Current IINQ LA1, LA2 connected to VIN – – 10 mA
VIN Sleep Current IINS EN = GND, VIN = 16 V – – 15 µA
Startup Time tON VIN > 7 V to ILA1 < –5 mA, RREF = 125 Ω 5 15 30 µs
Current Regulation
Reference Voltage VIREF 0.7 mA < IREF < 8.8 mA 1.15 1.2 1.25 V
Reference Current Ratio GHILAx / IREF – 25 – –
Current Accuracy3EILAx –20 mA > ILAx > –200 mA –5 ±4 5 %
Current Matching4EIMLAx
–40 mA > ILAx > –200 mA, VLAx match to
within 1 V – 5 10 %
Output Current ILAx
EN = high – GH ×
IREF
– –
IREF = 8 mA, EN = high –210 –200 –190 mA
Maximum Output Current ILAxmax IREF = 9.2 mA, EN = high – – –220 mA
Minimum Drop-out Voltage VDO
VIN – VLAx , ILAx = –200 mA – – 800 mV
VIN – VLAx , ILAx = –80 mA – – 660 mV
Current Slew Time Current rising or falling between 10% and 90% 50 80 110 µs
Logic Inputs EN and SW
Input Low Voltage VIL – – 0.8 V
Input High Voltage VIH 2 – – V
Input Hysteresis (EN pin) VIhys 150 350 – mV
Pull-Down Resistor (EN pin) RPD – 50 – kΩ
Pull-Up Current (SW pin) IPU – 100 – µA
SW Input Debounce Time tSW 10 – 50 ms
Protection
Short Detect Voltage VSCD Measured at LAx 1.2 – 1.8 V
Short Circuit Source Current ISCS Short present LAx to GND –4 –1.6 –1 mA
Short Release Voltage VSCR Measured at LAx – – 1.9 V
Short Release Voltage Hysteresis VSChys VSCR – VSCD 200 – 500 mV
Thermal Monitor Activation Temperature TJM TJ with ISEN = 90%, THTH open 95 115 130 °C
Thermal Monitor Slope dISEN/dTJISEN = 50%, THTH open –3.5 –2.5 –1.5 %/°C
Thermal Monitor Low Current
Temperature TJL TJ at ISEN = 25%, THTH open 120 135 150 °C
Overtemperature Shutdown TJF Temperature increasing – 170 – °C
Overtemperature Hysteresis TJhys Recovery = TJF – TJhys – 15 – °C
1For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
2Function is correct but parameters are not guaranteed outside the general limits (7 to 40 V).
3When EN = high, EILAx = 100 × [( | ILAx | × RREF / 30 ) –1], with ILAx in mA and RREF in kΩ.
4EIMLA = 100 × [ max ( | ILAx– ILA(AV) | ) / ILA(AV) ] , where ILA(AV) is the average current of all active outputs.
ELECTRICAL CHARACTERISTICS1 Valid at TJ = –40°C to 150°C, VIN = 7 to 40 V; unless otherwise noted
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
Automotive LED Array Driver
A6269
5
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
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Functional Description
The A6269 is a linear current regulator that is designed to provide
drive current and protection for parallel strings of series-connected
high brightness LEDs in automotive applications. It provides up to
two matched programmable current outputs at up to 200 mA, with
low minimum dropout voltages below the main supply voltage. For
12Vpowernetapplications,optimumperformanceisachieved
when driving 2 strings of 1 to 3 LEDs, at current up to 200 mA per
string.
The A6269 is specifically designed for use in internal illumina-
tion applications where the LED activity is controlled by a PWM
signal, by a logic signal, or by a push-to-make, ground-connected
switch.
Current regulation is maintained and the LEDs protected during a
short to ground at any point in the LED string. A short to ground on
any regulator output terminal will disable that output until the short
is removed. Open load on any output will be ignored.
Integrated thermal management reduces the regulated current level
at high internal junction temperatures to limit power dissipation.
Pin Functions
VIN Supply to the control circuit and current regulators. A small
value ceramic bypass capacitor, typically 100 nF, should be con-
nected from close to this pin to the GND pin.
GND Ground reference connection. Should be connected directly
to the negative supply.
EN Logic input to enable LED current output. This provides a
direct on/off action and can be used for direct PWM control. Note
that PWM dimming can only be applied when the LED is initially
in the off state. If the LED is already turned on using SW input, it
will remain on regardless of EN.
SW Logic input to toggle LED current output on and off. A single
push-to-make switch between SW and GND will provide push-
to-make/push-to-break, on/off toggle action. The SW input is
debounced by typically 30 ms and is internally pulled to typically
3V,withapproximately100µA.
IREF1.2Vreferencetosetcurrentreference.Connectresistor,
RREF
, to GND to set reference current.
THTH Sets the thermal monitor threshold, TJM
, where the output
current starts to reduce with increasing temperature. Connecting
THTH directly to GND will disable the thermal monitor function.
LA1, LA2 Current source connected to the anode of the first LED
ineachstring.ConnectdirectlytoVINtodisabletherespective
output. In this document “LAx” indicates any one of the outputs.
LED Current Level
The LED current is controlled by a matching linear current regula-
torbetweentheVINpinandeachoftheLAxoutputs.Thebasic
equation that determines the nominal output current at each LAx
pin is:
Given EN = high,
ILAx =
RREF
K
(1)
where ILAx is in mA and RREFisinkΩ;Kis30.
The output current may be reduced from the set level by the ther-
mal monitor circuit.
Conversely the reference resistors may be calculated from:
ILAx
=
RREF
K
(2)
where ILAx is in mA and RREFisinkΩ.
For example, where the required current is 180 mA for both chan-
nels the resistor value will be:
180
= =
RREF 167 Ω
30
It is important to note that because the A6269 is a linear regulator,
the maximum regulated current is limited by the power dissipation
and the thermal management in the application. All current calcula-
tions assume adequate heatsinking for the dissipated power. Ther-
mal management is at least as important as the electrical design in
all applications. In high current high ambient temperature applica-
tions the thermal management is the most important aspect of the
systems design. The application section below provides further
detail on thermal management and the associated limitations.
Operation with Fewer LED Strings or Higher Currents
The A6269 may be configured to use fewer than the maximum
quantity of LED strings: by connecting outputs together for higher
currents, by leaving the outputs open, or by connecting the output
directlytoVINtodisabletheregulatorforthatoutput.
Automotive LED Array Driver
A6269
6
Allegro MicroSystems
955 Perimeter Road
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Sleep Mode
When EN is held low the A6269 will be in shutdown mode and all
sections will be in a low power sleep mode. The input current will
betypicallylessthan10µA.Thismeansthatthecompletecircuit,
including LEDs, may remain connected to the power supply under
all conditions.
Safety Features
The circuit includes several features to ensure safe operation and to
protect the LEDs and the A6269:
•ThecurrentregulatorsbetweenVINandeachLAxoutputpro-
vide a natural current limit due to the regulation.
• Each LAx output includes a short-to-ground detector that will
disable the output to limit the dissipation.
• The thermal monitor reduces the regulated current as the tem-
perature rises.
• Thermal shutdown completely disables the outputs under extreme
overtemperature conditions.
Short Circuit Detection A short to ground on any LED cathode
(figure 1A) will not result in a short fault condition. The current
through the remaining LEDs will remain in regulation and the
LEDs will be protected. Due to the difference in the voltage drop
across the LEDs, as a result of the short, the current matching in
the A6269 may exceed the specified limits.
Any LAx output that is pulled below the short detect voltage (fig-
ure 1B) will disable the regulator on that output. A small current
will be sourced from the disabled output to monitor the short and
detect when it is removed. When the voltage at LAx rises above the
short detect voltage, the regulator will be re-enabled.
A shorted LED (figure 1C) will not result in a short fault condition.
The current through the remaining LEDs will remain in regula-
tion and the LEDs will be protected. Due to the difference in the
voltage drop across the LEDs, as a result of the short, the current
matching in the A6269 may exceed the specified limits.
A short between LEDs in different strings (figure 1D) will not
result in a short fault condition. The current through the remaining
LEDs will remain in regulation and the LEDs will be protected.
The current will be summed and shared by the affected strings.
Current matching in the strings will then depend on the LED for-
ward voltage differences.
A6269
VIN
GND
LA2
LA1
A6269
VIN
GND
LA2
LA1
A6269
VIN
GND
LA2
LA1
A6269
VIN
GND
LA2
LA1
A. Any LED cathode short to ground.
Current remains regulated in
non-shorted LEDs. Matching may be
affected.
B. Any LAx output short to ground.
Shorted output is disabled. Other
outputs remain active.
C. Current remains regulated.
Matching may be affected.
Only the shorted LED is inactive.
D. Short between LEDs in different
strings. Current remains regulated.
Current is summed and shared by
affected strings. Intensity match
dependent on voltage binning.
Figure 1. Short circuit conditions.
Automotive LED Array Driver
A6269
7
Allegro MicroSystems
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
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Temperature Monitor A temperature monitor function, included
in the A6269, reduces the LED current as the silicon junction
temperature of the A6269 increases (see figure 2). By mounting the
A6269 on the same thermal substrate as the LEDs, this feature can
also be used to limit the dissipation of the LEDs. As the junction
temperature of the A6269 increases, the regulated current level is
reduced, reducing the dissipated power in the A6269 and in the
LEDs. The current is reduced from the 100% level at typically
2.5% per degree Celsius until the point at which the current drops
to 25% of the full value, defined at TJL
. Above this temperature the
current will continue to reduce at a lower rate until the temperature
reaches the overtemperature shutdown threshold temperature, TJF.
The temperature at which the current reduction begins can be
adjusted by changing the voltage on the THTH pin. When THTH
is left open the temperature at which the current reduction begins is
defined as the thermal monitor activation temperature, TJM, and is
specified, in the characteristics table, at the 90% current level.
Thermal monitor activation temperature can be set to a desired
levelbysettingthevoltageontheTHTHpin(VTHTH). There is an
internal1VsourceconnectedwithaseriesresistortotheTHTH
pin inside the IC. A resistor connected between THTH and GND
willreduceVTHTH and increase TJM. A resistor connected between
THTHandareferencesupplygreaterthan1VwillincreaseVTHTH
and reduce TJM. Figure 3a shows the relationship between TJM and
VTHTH while Figure 3b shows typical resistor values, either pull up
or pull down, to set the voltage on THTH pin. Now, based on the
TJMrequirement,estimatetherequiredVTHTH voltage from Figure
3a,andthen,dependingontheVTHTH value, decide the THTH pin
resistor from Figure 3b. THTH pin resistor may either pull up or
pulldowndependingonVTHTH. As an example, if TJM of 90°C
isrequired,thenfromFigure3a,VTHTHshouldbe1.115V.To
achieve this voltage, use Figure 3b to estimate THTH pin resistor
(RTH).Ifthepull-upvoltageis5V,thena211kΩresistorshould
beused.Ifthepull-upvoltageis3V,usea100kΩresistor.
In extreme cases, if the chip temperature exceeds the overtempera-
ture limit, TJF
, all regulators will be disabled. The temperature will
continue to be monitored and the regulators reactivated when the
temperature drops below the threshold provided by the specified
hysteresis.
Note that it is possible for the A6269 to transition rapidly between
thermal shutdown and normal operation. This can happen if the
thermal mass attached to the exposed thermal pad is small and TJM
is increased to close to the shutdown temperature. The period of
oscillation will depend on TJM
, the dissipated power, the thermal
mass of any heatsink present, and the ambient temperature.
Figure 2. Temperature monitor current reduction.
Figure 3a. Relationship between TJM and VTHTH.Figure 3b. Typical Resistor Values to Set Voltage on THTH Pin.
0.8
0.85
0.9
0.95
1
1.05
1.1
1.15
1.2
1.25
70 80 90 100 110 120 130 140 150
VTHTH (V)
Thermal Monitor Acvaon Temperature, TJM (°C )
0.80
0.85
0.90
0.95
1.00
1.05
1.10
1.15
1.20
1.25
0 50 100 150 200 250
VTHTH (V)
RTH (kΩ)
RTH Pull down to GND
RTH Pull up to 5 V
RTH Pull up to 3 V
0
10
20
30
40
50
60
70
80
90
100
110
70 80 90 100 110 120 130 140 150 160 170 180
Relave Sense Current (%)
Juncon Temperature, TJ (°C)
T
JM
T
JL
Automotive LED Array Driver
A6269
8
Allegro MicroSystems
955 Perimeter Road
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Application Information
Power Dissipation
The most critical design considerations when using a linear regu-
lator such as the A6269 are the power produced internally as heat
and the rate at which that heat can be dissipated.
There are three sources of power dissipation in the A6269:
• The quiescent power to run the control circuits
• The power in the reference circuit
• The power due to the regulator voltage drop
The elements relating to these dissipation sources are illustrated
infigure4.
Quiescent Power The quiescent power is the product of the
quiescent current, IINQ
,andthesupplyvoltage,VIN , and is not
related to the regulated current. The quiescent power, PQ, is there-
fore defined as:
PQ = VIN × IINQ (3)
Reference Power The reference circuit draws the reference
current from the supply and passes it through the reference resis-
tor to ground. The reference current is 8% of the output current
on any one active output. The reference circuit power is the prod-
uct of the reference current and the difference between the supply
voltageandthereferencevoltage,typically1.2V.Thereference
power, PREF , is therefore defined as:
PREF =
RREF
(VIN – VREF) × VREF
(4)
Regulator Power In most application circuits the largest dis-
sipation will be produced by the output current regulators. The
power dissipated in each current regulator is simply the product
of the output current and the voltage drop across the regulator.
The total current regulator dissipation is the sum of the dissipa-
tion in each output regulator. The regulator power for each output
is defined as:
PREGx =(VIN – VLEDx ) × ILEDx
(5)
where x is 1 or 2.
Notethatthevoltagedropacrosstheregulator,VREG , is always
greaterthanthespecifiedminimumdrop-outvoltage,VDO
. The
output current is regulated by making this voltage large enough
to provide the voltage drop from the supply voltage to the total
forwardvoltageofallLEDsinseries,VLED .
The total power dissipated in the A6269 is the sum of the qui-
escent power, the reference power, and the power in each of the
regulators:
P
DIS
=P
Q
+ P
REF
+ PREGA + PREGB + PREGC + PREGD
(6)
The power that is dissipated in each string of LEDs is:
PLEDx =VLEDx × ILEDx
(7)
wherexisA,B,C,orD,andVLEDx is the voltage across all
LEDs in the string.
Figure 4. Internal power dissipation sources.
A6269
LAx
ILAx
IINQ
IREF
VIN
GND
IREF
RREF
VREF
VLED
VREG
VIN
Automotive LED Array Driver
A6269
9
Allegro MicroSystems
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From these equations (and as illustrated in figure 5) it can be seen
that, if the power in the A6269 is not limited, then it will increase
as the supply voltage increases but the power in the LEDs will
remain constant.
Dissipation Limits
There are two features limiting the power that can be dissipated
by the A6269: thermal shutdown and thermal foldback.
Thermal Shutdown If the thermal foldback feature is disabled
by connecting the THTH pin to GND, or if the thermal resistance
from the A6269 to the ambient environment is high, then the
silicon temperature will rise to the thermal shutdown threshold
and the current will be disabled. After the current is disabled the
power dissipated will drop and the temperature will fall. When
the temperature falls by the hysteresis of the thermal shutdown
circuit, then the current will be re-enabled and the temperature
will start to rise again. This cycle will repeat continuously until
the ambient temperature drops or the A6269 is switched off. The
period of this thermal shutdown cycle will depend on several
electrical, mechanical, and thermal parameters, and could be from
a few milliseconds to a few seconds.
Thermal Foldback If there is a good thermal connection to the
A6269, then the thermal foldback feature will have time to act.
This will limit the silicon temperature by reducing the regulated
current and therefore the dissipation.
The thermal monitor will reduce the LED current as the tempera-
ture of the A6269 increases above the thermal monitor activation
temperature, TJM , as shown in figure 6. The figure shows the
operation of the A6269 with 2 strings of 3 red LEDs, each string
runningat100mA.TheforwardvoltageofeachLEDis2.3Vand
the graph shows the current as the supply voltage increases from
14to17V.Asthesupplyvoltageincreases,withoutthethermal
foldback feature, the current would remain at 100 mA, as shown
by the dashed line. The solid line shows the resulting current
decrease as the thermal foldback feature acts.
If the thermal foldback feature did not affect LED current, the
current would increase the power dissipation and therefore the
silicon temperature. The thermal foldback feature reduces power
in the A6269 in order to limit the temperature increase, as shown
in figure 7. The figure shows the operation of the A6269 under
the same conditions as figure 6. That is, 2 strings of 3 red LEDs,
each string running at 100 mA with each LED forward voltage
Figure 5. Power Dissipation versus Supply Voltage
3.0
2.5
2.0
1.5
1.0
0.5
0
A6269 Power
Supply Voltage, V
IN
(V)
Power Dissipation, PD (W)
LED Power
2 Strings
VLED = 6.9 V
ILED = 100 mA
8 9 1110 1312 161514
Figure 6. LED current versus Supply Voltage
Figure 7. Junction Temperature versus Supply Voltage
54
52
50
48
46
44
42
40
Without thermal monitor
With thermal monitor
14.0 14.5 15.0 16.0 17.015.5
Supply Voltage, VIN (V)
ILED (mA)
16.5
2 Strings
VLED = 6.9 V
ILED = 100 mA
TA = 50°C
130
125
120
115
110
105
100
Without thermal monitor
With thermal monitor
14.0 14.5 15.0 16.0 17.015.5
Supply Voltage, VIN (V)
TJ (°C)
16.5
2 Strings
VLED = 6.9 V
ILED = 100 mA
TA = 50°C
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A6269
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at2.3V.Thegraphshowsthetemperatureasthesupplyvoltage
increasesfrom14to17V.Withoutthethermalfoldbackfeature
the temperature would continue to increase up to the thermal
shutdown temperature as shown by the dashed line. The solid line
shows the effect of the thermal foldback function in limiting the
temperature rise.
Figures 6 and 7 show the thermal effects where the thermal
resistancefromthesilicontotheambienttemperatureis40°C/W.
Thermal performance can be enhanced further by using a signifi-
cant amount of thermal vias as described below.
Supply Voltage Limits
In many applications, especially in automotive systems, the avail-
able supply voltage can vary over a two-to-one range, or greater
when double battery or load dump conditions are taken into con-
sideration. In such systems is it necessary to design the applica-
tion circuit such that the system meets the required performance
targets over a specified voltage range.
To determine this range when using the A6269 there are two
limiting conditions:
• For maximum supply voltage the limiting factor is the power
that can be dissipated from the regulator without exceeding the
temperature at which the thermal foldback starts to reduce the
output current below an acceptable level.
• For minimum supply voltage the limiting factor is the maximum
drop-out voltage of the regulator, where the difference between
the load voltage and the supply is insufficient for the regulator
to maintain control over the output current.
Minimum Supply Limit: Regulator Saturation Voltage
Thesupplyvoltage,VIN
, is always the sum of the voltage drop
acrossthehigh-sideregulator,VREG , and the forward voltage of
theLEDsinthestring,VLED,asshowninfigure4.
VLED is constant for a given current and does not vary with
supplyvoltage.ThereforeVREG provides the variable difference
betweenVLEDandVIN. V REG has a minimum value below which
the regulator can no longer be guaranteed to maintain the output
current within the specified accuracy. This level is defined as the
regulatordrop-outvoltage,VDO.
The minimum supply voltage, below which the LED current does
not meet the specified accuracy, is therefore determined by the
sumoftheminimumdrop-outvoltage,VDO , and the forward
voltageoftheLEDsinthestring,VLED . The supply voltage must
always be greater than this value and the minimum specified sup-
ply voltage, that is:
VIN > VDO + VLED, and
VIN > VIN
(min) (8)
As an example, consider the configuration used in figures 6 and
7 above, namely 2 strings of 3 red LEDs, each string running at
100mA,witheachLEDforwardvoltageat2.3V.Theminimum
supply voltage will be approximately:
VIN(min) = 0.55 + (3 ×2.3)=7.45V
Maximum Supply Limit: Thermal Limitation As described
above, when the thermal monitor reaches the activation tempera-
ture, TJM (due to increased power dissipation as the supply volt-
age rises), the thermal foldback feature causes the output current
to decrease. The maximum supply voltage is therefore defined as
the voltage above which the LED current drops below the accept-
able minimum.
This can be estimated by determining the maximum power that
can be dissipated before the internal (junction) temperature of the
A6269 reaches TJM.
Note that, if the thermal monitor circuit is disabled (by connect-
ing the THTH pin to GND), then the maximum supply limit will
be the specified maximum continuous operating temperature,
150°C.
The maximum power dissipation is therefore defined as:
PD(max) =RθJA
∆T(max)
(9)
whereΔT(max)isdifferencebetweenthethermalmonitoractiva-
tion temperature, TJM
, of the A6269 and the maximum ambient
temperature, TA(max), and RθJA is the thermal resistance from the
internal junctions in the silicon to the ambient environment.
If minimum LED current is not a critical factor, then the maxi-
mum voltage is simply the absolute maximum specified in the
parameter tables above.
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Thermal Dissipation
The amount of heat that can pass from the silicon of the A6269
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A6269. The thermal
resistance, RθJA
, is a measure of the temperature rise created by
power dissipation and is usually measured in degrees Celsius per
watt (°C/W).
Thetemperaturerise,ΔT,iscalculatedfromthepowerdissipated,
PD
, and the thermal resistance, RθJA
, as:
 ΔT = PD × RθJA (10)
A thermal resistance from silicon to ambient, RθJA
, of approxi-
mately 35°C/W can be achieved by mounting the A6269 on a
standardFR4double-sidedprintedcircuitboard(PCB)witha
copper area of a few square inches on each side of the board
under the A6269. Additional improvements in the range of 20%
may be achieved by optimizing the PCB design.
Optimizing Thermal Layout
The features of the printed circuit board, including heat conduc-
tion and adjacent thermal sources such as other components,
have a very significant effect on the thermal performance of the
device. To optimize thermal performance, the following should
be taken into account:
• The device exposed thermal pad should be connected to as
much copper area as is available.
• Copper thickness should be as high as possible (for example,
2 oz. or greater for higher power applications).
• The greater the quantity of thermal vias, the better the dissipa-
tion. If the expense of vias is a concern, studies have shown
that concentrating the vias directly under the device in a tight
pattern, as shown in figure 8, has the greatest effect.
• Additional exposed copper area on the opposite side of the
board should be connected by means of the thermal vias. The
copper should cover as much area as possible.
• Other thermal sources should be placed as remote from the
device as possible
Ø0.3 mm via
Top-layer
exposed copper
Signal traces
LJ package
exposed
thermal pad
LJ package
footprint
0.7 mm
0.7 mm
Figure 8. Suggested PCB layout for thermal optimization
(maximum available bottom-layer copper recommended)
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Application Examples
Operation with High-Side PWM Supply In some filament
bulb replacement applications the supply may be provided by a
PWM-driven high-side switch. The A6269 can be used in this
applicationbysimplyconnectingENtoVIN.
The toggle action of the SW input will be reset to off at each
power-up. From this stage, applying an EN = high signal turns
the LED on, and an EN = low turns the LED off.
Whenpowerisapplied(withENconnectedtoVIN),therewill
be a short startup delay, tON , before the current starts to rise. The
rise time of the current will be limited by the internal current slew
rate control.
Figures 9a to 9c show application circuit options, including a
higher voltage supply, and combinations of outputs tied together
and disabled.
Operation with both EN and SW In some applications it
may be required to utilize the functionality of both the EN input
and the SW input. For example in dome lighting (see figure 10),
a manual switch may be used to toggle the light on or off. While
the light is in the off state, the central lighting control unit may
send a PWM signal to dim the light gradually before turning off
completely. The interaction of the two control inputs is explained
below:
• Internal flip-flop (hence LED light) starts from off state, en-
sured by power-on reset.
• The light can be turned on by either EN = high or by a momen-
tarytoggle(high→low→high)attheSWinput.
• If the light is initially turned on by EN = high, it can be turned
off by EN = low. This allows PWM dimming of the light.
• If the light is initially turned on by SW input, it stays on regard-
less of the state of EN. The light goes off only when another
momentary toggle is received at the SW input, or when the
power is removed.
The behavior above is graphically represented by the state dia-
gram in figure 11. Note that the manual SW input always take
precedence over the EN/PWM dimming input.
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A6269
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A6269
+
–
VIN
12 V PWM
high-side drive
GND
LA1
LA2
LA1
LA2
LA1
LA2
LA1
LA2
EN
SW
IREF
THTH
A6269
+
–
VIN
Automotive
24 V power net
GND
EN
SW
IREF
THTH
A6269
+
–
VIN
Automotive
12 V power net
GND
EN
SW
IREF
THTH
On/Off
A6269
+
–
VIN
Automotive
24 V power net
PWM dimming
input from LCU
GND
EN
SW
IREF
THTH
On/Off
On/Off
Start
LED = Off
LED = On
EN = H
EN = H
PWM Dimming
SW = momentarily shorted
to GND to toggle EN = L
SW = H
SW = SW =
EN = L
LED = On
LED = Off
SW =
Figure 10. Typical applications using SW and EN together Figure 11. State diagram when both SW and EN are used
Figure 9. Typical applications with various supply and output options.
B. Higher voltage operation
C. Mix of output combinations
A. High brightness (HB) LED incandescent lamp replacement
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Binning Resistor Arrangement
An external binning resistor can be connected in series with the
IREF pin to set appropriate current through various LED batches.
A filter capacitor of 100 nF should be placed after RREF1 as
shown in Figure 12.
ILAx(min)=(K)÷(RREF1 + RREF2) (11)
ILAx(max)=(K)÷RREF1 (12)
A6269
LAx
VIN
LED Driver Board
GND
LAx
IREF
LED Board
CREF
RREF1
RREF2
LED1 LED2
LED3 LED4
Figure 12. Application Circuit for Binning – Current-setting resistor (RREF2)
can be placed on LED board for different bins of LEDs
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A6269
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Package LJ, 8-Pin SOICN with Exposed Thermal Pad
3.30
2
1
8
Reference land pattern layout (reference IPC7351
SOIC127P600X175-9AM); all pads a minimum of 0.20 mm from all
adjacent pads; adjust as necessary to meet application process
requirements and PCB layout tolerances; when mounting on a multilayer
PCB, thermal vias at the exposed thermal pad land can improve thermal
dissipation (reference EIA/JEDEC Standard JESD51-5)
PCB Layout Reference View
C
1.27
5.602.41
1.75
0.65
2.41 NOM
3.30 NOM
C
SEATING
PLANE
1.27 BSC
GAUGE PLANE
SEATING PLANE
ATerminal #1 mark area
B
C
B
21
8
C
SEATING
PLANE
C0.10
8X
0.25 BSC
1.04 REF
1.70 MAX
For Reference Only; not for tooling use (reference MS-012BA)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
4.90 ±0.10
3.90 ±0.10 6.00 ±0.20
0.51
0.31 0.15
0.00
0.25
0.17
1.27
0.40
8°
0°
Exposed thermal pad (bottom surface)
A
Branded Face
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A6269
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For the latest version of this document, visit our website:
www.allegromicro.com
Revision History
Number Date Description
7 June 24, 2013 Update Features List, fig. 5
8 August 11, 2016 Revised Temperature Monitor section (page 7) and added Binning Resistor Arrangement section
(page 14)
9 February 6, 2019 Product status changed to Pre-End-of-Life
10 July 1, 2019 Product status changed to Last Time Buy
Copyright 2019, Allegro MicroSystems.
Allegro MicroSystems reserves the right to make, from time to time, such departures from the detail specifications as may be required to permit
improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the
information being relied upon is current.
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