A6269 Datasheet

A6269
Automotive LED Array Driver
Features and Benefits
Description
▪ 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
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.
▪ Dome light, map light, space lighting, mood lighting
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.
Package: 8-pin SOICN with exposed
thermal pad (suffix LJ)
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.
Applications:
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.
Not to scale
Typical Application Diagram
+
Automotive
12 V power net
VIN
PWM dimming
input from LCU
A6269
EN
On/Off
SW
LA1
IREF
LA2
THTH
PAD
GND
–
A6269-DS, Rev. 7
200 mA
200 mA
A6269
Automotive LED Array Driver
Selection Guide
LED Outputs
Ambient Operating
Temperature, TA (°C)
2 at 200 mA each
–40 to 125
Part Number
A6269KLJTR-T
Packing
3000 pieces per 13-in. reel
Package
8-pin SOICN with exposed thermal pad,
3.9 × 4.9 mm case
Absolute Maximum Ratings1
Characteristic
Rating
Unit
–0.3 to 50
V
–0.3 to 50
V
Pins LA1, LA2
–0.3 to 50
V
Pins IREF, THTH, SW
–0.3 to 6.5
V
–40 to 125
°C
150
°C
175
°C
–55 to 150
°C
Load Supply Voltage
Symbol
Notes
VIN
Pin EN
Ambient Operating Temperature
Range2
TA
Maximum Continuous Junction
Temperature
TJ(max)
Transient Junction Temperature
TtJ
Storage Temperature Range
Tstg
K temperature range
Over temperature event not exceeding 10 s, lifetime duration
not exceeding 10 h, guaranteed by design characterization
1With
respect to GND.
2Limited by power dissipation.
Thermal Characteristics*may require derating at maximum conditions, see application section for optimization
Characteristic
Symbol
Package Thermal Resistance
(Junction to Ambient)
RθJA
Package Thermal Resistance
(Junction to Pad)
RθJP
Test Conditions*
Value
Unit
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
2
ºC/W
*Additional thermal information available on the Allegro™ website.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A6269
Automotive LED Array Driver
Functional Block Diagram
VBAT
VIN
D
SW
C
Deglitch
Q
R
Q
Power-On
Reset
Current
Regulators
Control
Logic
EN
LA1
THTH
IREF
Temp
Comp
Temp
Monitor
LA2
Slew
Limit
Current
Reference
RTH
RREF
PAD
GND
Terminal List Table
Pin-out Diagram
8 SW
Number
Name
1
THTH
Function
2
IREF
Current reference
3
GND
Ground reference
Thermal threshold
THTH
1
IREF
2
GND
3
6 VIN
4
LA1
LED anode (+) connection 1
LA1
4
5 LA2
5
LA2
LED anode (+) connection 2
6
VIN
Supply
7
EN
Enable
8
SW
Switch input
–
PAD
Exposed thermal pad
PAD
7 EN
LJ Package
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115 Northeast Cutoff
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3
A6269
Automotive LED Array Driver
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
Supply and Reference
VIN Functional Operating Range2
6
–
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
Reference Current Ratio
Current Accuracy3
Current Matching4
Output Current
VIREF
GH
EILAx
EIMLAx
ILAx
0.7 mA < IREF < 8.8 mA
1.15
1.2
1.25
V
ILAx / IREF
–
25
–
–
–20 mA > ILAx > –200 mA
–5
±4
5
%
–40 mA > ILAx > –200 mA, VLAx match to
within 1 V
–
5
10
%
EN = high
–
GH ×
IREF
–
–
IREF = 8 mA, EN = high
Maximum Output Current
Minimum Drop-out Voltage
ILAxmax
VDO
Current Slew Time
–210
–200
–190
mA
IREF = 9.2 mA, EN = high
–
–
–220
mA
VIN – VLAx , ILAx = –200 mA
–
–
800
mV
VIN – VLAx , ILAx = –80 mA
–
–
660
mV
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
VSCR
Measured at LAx
–
–
1.9
V
200
–
500
mV
Short Release Voltage
Short Release Voltage Hysteresis
Thermal Monitor Activation Temperature
Thermal Monitor Slope
VSChys
TJM
dISEN/dTJ
VSCR – VSCD
TJ with ISEN = 90%, THTH open
95
115
130
°C
ISEN = 50%, THTH open
–3.5
–2.5
–1.5
%/°C
120
135
150
°C
Thermal Monitor Low Current
Temperature
TJL
TJ at ISEN = 25%, THTH open
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, E
ILAx = 100 × [( | ILAx | × RREF / 30 ) –1], with ILAx in mA and RREF in kΩ.
4E
IMLA = 100 × [ max ( | ILAx– ILA(AV) | ) / ILA(AV) ] , where ILA(AV) is the average current of all active outputs.
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A6269
Automotive LED Array Driver
Functional Description
The A6269 is a linear current regulator that is designed to provide drive current and protection for parallel strings of seriesconnected 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 illumination 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 connected 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 regulator 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 =
K
(1)
RREF
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 thermal monitor circuit.
Conversely the reference resistors may be calculated from:
K
ILAx
where ILAx is in mA and RREF is in kΩ.
RREF =
(2)
For example, where the required current is 180 mA for both channels the resistor value will be:
RREF = 30 = 167 Ω
180
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 calculations assume adequate heatsinking for the dissipated power. Thermal management is at least as important as the
electrical design in all applications. In high current high ambient
temperature applications 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.
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A6269
Automotive LED Array Driver
VIN
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 provide 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 temperature 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 (figure 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
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.
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 forward voltage differences.
A. Any LED cathode short to ground.
Current remains regulated in
non-shorted LEDs. Matching may be
affected.
A6269
LA1
LA2
GND
VIN
A6269
B. Any LAx output short to ground.
Shorted output is disabled. Other
outputs remain active.
LA1
LA2
GND
VIN
A6269
C. Current remains regulated.
Matching may be affected.
Only the shorted LED is inactive.
LA1
LA2
GND
VIN
D. Short between LEDs in different
strings. Current remains regulated.
Current is summed and shared by
affected strings. Intensity match
dependent on voltage binning.
A6269
LA1
LA2
GND
Figure 1. Short circuit conditions.
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A6269
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.
100
Relative Sense Current (%)
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 4% 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.
Automotive LED Array Driver
90
80
60
TJM
40
25
20
TJF
TJL
0
70
130
90
110
Junction Temperature, TJ (°C)
150
170
Figure 2. Temperature monitor current reduction.
TJM will increase as the voltage at the THTH pin, VTHTH , is
reduced and is defined as approximately:
TJM = 1.46 –VTHTH (°C)
(3)
0.0039
A resistor connected between THTH and GND will reduce VTHTII
and increase TJM. A resistor connected between THTH and a reference supply greater than 1 V will increase VTHTH and reduce TJM.
In extreme cases, if the chip temperature exceeds the overtemperature limit, TJF , all regulators will be disabled. The temperature will continue to be monitored and the regulators re-activated
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.
1.2
200
1.1
150
RTH pull-down
to GND
100
50
0
70
1.0
VTHTH
0.9
RTH pull-up
to 3 V
80
VTHTH (V)
RTH pull-up
to 5 V
RTH (kΩ)
Figure 3 shows how the nominal value of the thermal monitor
activation temperature varies with the voltage at THTH and with
either a pull-down resistor, RTH, to GND or with a pull-up resistor, RTH , to 3 V and to 5 V.
1.3
250
90
100
110
120
130
140
Thermal Monitor Activation Temperature, TJM (°C)
0.8
150
Figure 3. TJM versus a pull-up or pull-down resistor, RTH, and VTHTH.
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A6269
Automotive LED Array Driver
Application Information
Power Dissipation
The most critical design considerations when using a linear regulator 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:
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 quiescent power, the reference power, and the power in each of the
regulators:
• The quiescent power to run the control circuits
• The power in the reference circuit
• The power due to the regulator voltage drop
PDIS = PQ + PREF
+ PREGA + PREGB + PREGC + PREGD
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 therefore defined as:
PQ = VIN × IINQ
(4)
The power that is dissipated in each string of LEDs is:
PLEDx = VLEDx × ILEDx
(VIN – VREF) × VREF
VIN
A6269
VREG
ILAx
LAx
(5)
RREF
Regulator Power In most application circuits the largest dissipation 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 dissipation in each output regulator. The regulator power for each output
is defined as:
PREGx = (VIN – VLEDx ) × ILEDx
where x is 1 or 2.
(8)
where x is A, B, C, or D, and VLEDx is the voltage across all
LEDs in the string.
Reference Power The reference circuit draws the reference
current from the supply and passes it through the reference resistor to ground. The reference current is 8% of the output current
on any one active output. The reference circuit power is the product 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 =
(7)
VIN
IREF
IINQ
VLED
IREF
VREF
RREF
GND
(6)
Figure 4. Internal power dissipation sources.
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A6269
Automotive LED Array Driver
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.
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
54
52
Without thermal monitor
50
ILED (mA)
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.
48
46
44
The thermal monitor will reduce the LED current as the temperature of the A6269 increases above the thermal monitor activation
temperature, TJM , as shown in figure 6. The figure shows the
With thermal monitor
2 Strings
VLED = 6.9 V
ILED = 100 mA
TA = 50°C
42
40
14.0
14.5
15.0
15.5
16.0
Supply Voltage, VIN (V)
16.5
17.0
Figure 6. LED current versus Supply Voltage
3.0
130
125
2.0
120
TJ (°C)
Power Dissipation, PD (W)
2.5
1.5
LED Power
1.0
A6269 Power
0.5
0
8
9
10
Figure 5. Power Dissipation versus Supply Voltage
14
15
115
Without thermal monitor
With thermal monitor
110
2 Strings
VLED = 6.9 V
ILED = 100 mA
11
12
13
Supply Voltage, VIN (V)
2 Strings
VLED = 6.9 V
ILED = 100 mA
TA = 50°C
105
16
100
14.0
14.5
15.0
15.5
16.0
Supply Voltage, VIN (V)
16.5
17.0
Figure 7. Junction Temperature versus Supply Voltage
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A6269
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 significant amount of thermal vias as described below.
Supply Voltage Limits
In many applications, especially in automotive systems, the available supply voltage can vary over a two-to-one range, or greater
when double battery or load dump conditions are taken into consideration. In such systems is it necessary to design the application 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 . VREG 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
Automotive LED Array Driver
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 supply voltage, that is:
VIN > VDO + VLED, and
VIN > VIN (min)
(9)
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 temperature, TJM (due to increased power dissipation as the supply voltage 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 acceptable 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 connecting 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) =
∆T(max)
RθJA
(10)
where ΔT(max) is difference between the thermal monitor activation 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 maximum voltage is simply the absolute maximum specified in the
parameter tables above.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
A6269
Automotive LED Array Driver
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
(11)
A thermal resistance from silicon to ambient, RθJA , of approximately 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 conduction 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 dissipation. 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
Signal traces
LJ package
footprint
0.7 mm
0.7 mm
LJ package
exposed
thermal pad
Top-layer
exposed copper
Ø0.3 mm via
Figure 8. Suggested PCB layout for thermal optimization
(maximum available bottom-layer copper recommended)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
A6269
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
Automotive LED Array Driver
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, ensured by power-on reset.
• The light can be turned on by either EN = high or by a momentary 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 regardless 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 diagram in figure 11. Note that the manual SW input always take
precedence over the EN/PWM dimming input.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
A6269
Automotive LED Array Driver
+
+
12 V PWM
high-side drive
Automotive
24 V power net
VIN
VIN
A6269
EN
A6269
LA1
LA1
On/Off
EN
SW
IREF
SW
LA2
IREF
LA2
THTH
THTH
GND
GND
–
–
A. High brightness (HB) LED incandescent lamp replacement
B. Higher voltage operation
+
Automotive
12 V power net
VIN
A6269
LA1
EN
On/Off
SW
IREF
LA2
THTH
GND
–
C. Mix of output combinations
Figure 9. Typical applications with various supply and output options.
+
Automotive
24 V power net
SW = momentarily shorted
to GND to toggle
VIN
PWM dimming
input from LCU
EN = L
SW = H
EN = H
A6269
EN
EN = H
LA1
On/Off
Start
LED = Off
LED = On
SW
IREF
EN = L
LED = Off
PWM Dimming
LA2
THTH
SW =
GND
–
Figure 10. Typical applications using SW and EN together
SW =
SW =
LED = On
Figure 11. State diagram when both SW and EN are used
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
A6269
Automotive LED Array Driver
Package LJ, 8-Pin SOICN with Exposed Thermal Pad
4.90 ±0.10
0.65
8°
0°
8
0.25
0.17
B
2.41 NOM
A
1
3.90 ±0.10
6.00 ±0.20
SEATING PLANE
GAUGE PLANE
Branded Face
1.27 BSC
1
1.27
0.40
0.25 BSC
0.51
0.31
2.41
2
SEATING
PLANE
0.10 C
C
5.60
2
3.30
C
PCB Layout Reference View
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
1.70 MAX
0.15
0.00
1.27
1.04 REF
3.30 NOM
8X
8
1.75
A Terminal #1 mark area
B
Exposed thermal pad (bottom surface)
C
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)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
14
A6269
Automotive LED Array Driver
Revision History
Revision
Revision Date
Rev. 7
June 24, 2013
Description of Revision
Update Features List, fig. 5
Copyright ©2009-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC 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.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
15
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