Allegro A6263 Protected led array driver Datasheet

A6263
Protected LED Array Driver
Features and Benefits
Description
▪ AEC-Q100 qualified
▪ Total LED drive current up to 400 mA
▪ Current shared equally up to 100 mA by up to 4 strings
▪ Wide input voltage range of 6 to 50 V for start/stop, cold
crank, and load dump requirements
▪ Low dropout voltage
• LED current levels set by single reference resistor
• LED string shorted to GND protection
• Overtemperature protection with optional thermal
derating function
▪ Automotive temperature range
The A6263 is a linear, programmable current regulator providing
up to 100 mA from each of 4 outputs to drive arrays of high
brightness LEDs. Outputs can be connected in parallel or left
unused, as required. 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.
The IC provides protection against the following common
faults:
• LED string shorted to GND
• Single or multiple LED short
Applications:
• LED string open
▪ Automotive interior and exterior lighting
• IC pin open/short
• Overtemperature
Package: 8-pin SOICN with exposed
thermal pad (suffix LJ)
If one LED string is open or shorted to ground, the offending
string is disabled, while other LED strings continue to work.
A temperature monitor is included to reduce the LED drive
current if the chip temperature exceeds a thermal threshold.
If necessary, this thermal derating threshold can be adjusted
or disabled.
The device comes in an 8-pin SOIC ( package 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
Light Switch
100 nF
VIN
+
Automotive
12 V power net
–
A6263
LA1
LA2
IREF
LA3
THTH
LA4
100 mA
100 mA
100 mA
100 mA
PAD
GND
Figure 1. Typical application circuit
A6263-DS
1 to 3 LEDs
in series
A6263
Protected LED Array Driver
Selection Guide
Part Number
Ambient Operating
Temperature, TA (°C)
A6263KLJTR-T
–40 to 125
*Contact Allegro™ for additional packing options.
Packing*
3000 pieces per 13-in. reel
Package
8-pin SOICN with exposed thermal pad
Absolute Maximum Ratings*
Characteristic
Input Supply Voltage
Symbol
Notes
VIN
Rating
Unit
–0.3 to 50
V
Pins LA1 through LA2
–0.3 to 50
V
Pins IREF and THTH
–0.3 to 6.5
V
–40 to 125
°C
150
°C
175
°C
–55 to 150
°C
Ambient Operating Temperature
Range
TA
Maximum Continuous Junction
Temperature
TJ(max)
Transient Junction Temperature
TtJ
Storage Temperature Range
Tstg
K temperature range
Overtemperature event not exceeding 10 s, lifetime duration
not exceeding 10 h, guaranteed by design characterization
*Stresses beyond those listed in this table may cause permanent damage to the device. The Absolute Maximum ratings are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in the Electrical Characteristics table is not implied.
Exposure to Absolute Maximum-rated conditions for extended periods may affect device reliability.
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
A6263
Protected LED Array Driver
Functional Block Diagram
VIN
Thermal
Monitor
THTH
IREF
Current
Regulators
Current Reference
IREF
Control
LA1
LA2
LA3
Overtemperature
Fault
Control
LED Open
LA4
LED String
Short to GND
PAD
GND
Terminal List Table
Number
Name
Function
1
THTH
Thermal Threshold. Short this pin to ground to disable
thermal derating feature, or leave open to enable. (Thermal
shutdown function is always enabled.)
2
IREF
Connect a reference resistor between this pin and GND to
set the LED current.
3
LA1
LED anode (+) connection 1*
Pin-out Diagram
THTH
1
IREF
2
LA1
3
6 LA4
4
LA2
LED anode (+) connection 2*
LA2
4
5 LA3
5
LA3
LED anode (+) connection 3*
6
LA4
LED anode (+) connection 4*
7
VIN
Input power to the IC. All LED current sources are enabled
while VIN is above UVLO level. Decouple with a 0.1 μF
capacitor to GND near the IC.
8
GND
IC ground reference. Connect to ground plane(s) of the
PCB using the shortest path possible.
–
PAD
Exposed pad of the package providing enhanced thermal
dissipation. This pad must be connected to the ground
plane(s) of the PCB with at least 8 vias located directly in
the solder land for the pad.
8 GND
PAD
7 VIN
* If any LAx pin is unused, tie it to the VIN pin. Do not leave it open or shorted to GND.
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115 Northeast Cutoff
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A6263
Protected LED Array Driver
ELECTRICAL CHARACTERISTICS1 Valid at TA = 25°C, VIN = 7 to 40 V;
indicates specifications valid across the full operating
temperature range with TA = TJ = –40°C to 125°C and typical specifications at TA = 25°C; unless otherwise specified
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
6
–
50
V
Input Supply
Operating Input Voltage Range2
VIN
VIN Quiescent Current
IINQ
LAx pins connected to VIN
–
–
10
mA
Time3
tON
VIN > 7 V to ILA1 < –5 mA, RREF = 125 Ω
–
20
–
μs
1.15
1.2
1.25
V
6 V < VIN < 40 V
–
12.5
–
A /A
–10 mA > ILAx > –100 mA
–5
±4
5
%
–20 mA > ILAx > –100 mA, VLAx match to
within 1 V
–
5
10
%
–105
–100
–95
mA
IREF = 9.2 mA
–
–
–110
mA
VIN – VLAx , ILAx = –100 mA
–
–
800
mV
VIN – VLAx , ILAx = –40 mA
–
–
660
mV
Startup
Current Regulation
Reference Voltage
Reference Current Ratio
VIREF
GH
Current Accuracy4
EILAx
Current Matching5
EIMLAx
Output Current
Maximum Output Current
Minimum Drop-out Voltage
ILAx
ILAxmax
VDO
0.7 mA < IREF < 8.8 mA
IREF = 8 mA
Protection
Short Detect Voltage
VSCD
Measured at LAx
1.2
–
1.8
V
Short Circuit Source Current
ISCS
Short present from LAx to GND
–2
–0.8
–0.5
mA
Short Release Voltage
VSCR
Measured at LAx
–
–
1.9
V
VSCR – VSCD
200
–
500
mV
TJ with ISEN = 90%
95
115
130
°C
ISEN = 50%
–3.5
–2.5
–1.5
%/°C
TJL
TJ at ISEN = 25%
120
135
150
°C
Overtemperature Shutdown
TJF
Temperature increasing
–
170
–
°C
Overtemperature Hysteresis
TJhys
Recovery = TJF – TJhys
–
15
–
°C
Short Release Voltage Hysteresis
Thermal Monitor Activation Temperature
Thermal Monitor Slope
Thermal Monitor Low Current
Temperature
VSChys
TJM
dISEN/dTJ
1For
input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
is correct but parameters are not guaranteed outside the general limits (7 to 40 V).
3Ensured by design and characterization, not production tested.
4E
ILAx = 100 × [( | ILAx | × RREF / 15 ) –1], with ILAx in mA and RREF in kΩ.
5E
IMLA = 100 × max ( | ILAx– ILA(AV) | ) / ILA(AV) , where ILA(AV) is the average current of all active outputs.
2Function
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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A6263
Protected LED Array Driver
Functional Description
The A6263 is a linear current regulator that is designed to provide drive current and protection for parallel strings of seriesconnected high brightness LEDs. It provides up to 4 matched programmable current outputs at up to 100 mA, with low minimum
dropout voltages below the main supply voltage. For 12 V power
net applications, optimum performance is achieved when driving
4 strings of 1 to 3 LEDs, at current up to 100 mA per string.
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 disables that offending string
only. Similarly, in the case of an open output pin or an open-LED
fault, all other LED strings remain in regulation. Individual outputs can be disabled by connecting the output to VIN. Multiple
outputs can be connected in parallel to drive higher current LED
strings.
Integrated thermal management reduces the regulated current
level at high internal junction temperatures to limit power dissipation. This thermal threshold is programmable and can be
disabled if necessary.
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 ground plane of the circuit board.
IREF 1.2 V reference to set LED current. Connect resistor, RREF ,
to GND to set reference current and thereby LED 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.
LA[1:4] 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 4 matching linear current regulators, between the VIN pin and each of the LAx outputs. The
basic equation that determines the nominal output current at each
LAx pin is:
ILAx =
15
(1)
RREF
where ILAx is in mA and RREF is in kΩ.
The output current may be reduced from the set level by the thermal monitor circuit.
Conversely the reference resistors may be calculated from:
RREF = 15
ILAx
where ILAx is in mA and RREF is in kΩ.
(2)
For example, where the required current is 90 mA for both channels the resistor value will be:
RREF = 15 = 0.167 kΩ
90
These equations completely define the output currents with
respect to the setting resistors. However, for further reference, a
more detailed description of the internal reference current calculations is included below.
It is important to note that because the A6263 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 A6263 may be configured to use fewer than all four LED
strings, either by connecting outputs together for higher currents,
or by connecting the output directly to VIN to disable the regulator for that output. It is also acceptable, though not recommended,
to leave an unused LAx pin floating.
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115 Northeast Cutoff
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A6263
Temperature Monitor
A temperature monitor function reduces the LED current as the
silicon junction temperature of the IC increases (see figure 2). By
mounting the A6263 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 A6263 increases, the regulated
current level is reduced, reducing the dissipated power in the
A6263 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.
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.
100
TJM = 1.46 –VTHTH (°C)
(3)
0.0039
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 3 shows how the nominal value of the thermal monitor
activation temperature varies with the voltage at THTH and with
60
TJM
40
25
20
TJF
TJL
0
70
90
130
110
Junction Temperature, TJ (°C)
150
170
Figure 2. Temperature monitor current reduction
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 Electrical Characteristics table, at the 90%
current level.
1.3
250
1.2
200
RTH pull-up
to 5 V
RTH (kΩ)
TJM will increase as the voltage at the THTH pin, VTHTH , is
reduced and is defined as approximately:
90
80
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)
• 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.
• An open circuit on any output will disable the affected string
only.
• The thermal monitor reduces the regulated current as the temperature rises above a programmable thermal threshold.
• Thermal shutdown completely disables the outputs under extreme overtemperature conditions.
either a pull-down resistor, RTH, to GND or with a pull-up resistor, RTH , to 3 V and to 5 V.
Relative Sense Current (%)
Safety Features
The A6263 includes several features to ensure safe operation and
to protect the LEDs and the IC:
Protected LED Array Driver
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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A6263
Fault Cases
Protected LED Array Driver
VIN
A6263
LA1
LA2
LA3
LA4
Case A: Any LED cathode short to GND
GND
Outcome: IC continues to regulate current through all
LED strings. Current matching may suffer.
VIN
A6263
LA1
LA2
LA3
LA4
GND
Case B: LAx pin or high-side of LED string
shorted to GND
Outcome: IC detects pin-to-GND short before
enabling current regulators. Offending LED
string disabled. All other strings remain active.
VIN
A6263
LA1
LA2
LA3
LA4
Case C: Single LED in a string shorted
GND
Outcome: IC continues to regulate current through
all LED strings. Current matching may suffer.
VIN
A6263
LA1
LA2
LA3
LA4
GND
Case D: Short between LED strings
Outcome: LED current regulators continue to
operate normally, but current matching between
LED strings will be affected.
VIN
A6263
LA1
LA2
LA3
LA4
GND
Case E: LAx pin or high-side of LED string
open
Outcome: No current through the offending
LED string. All other strings remain active.
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115 Northeast Cutoff
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A6263
Protected LED Array Driver
Application Information
Power Dissipation
The most critical design considerations when using a linear regulator such as the A6263 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 A6263:
• The quiescent power to run the control circuits
• The power in the reference circuit
• The power due to the regulator voltage drop
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:
(4)
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 =
(VIN – VREF) × VREF
The total power dissipated in the A6263 is the sum of the quiescent power, the reference power, and the power in each of the
four regulators:
PDIS = PQ + PREF
+ PREGA + PREGB + PREGC + PREGD
The elements relating to these dissipation sources are illustrated
in figure 4.
PQ = VIN × IINQ
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 power that is dissipated in each string of LEDs is:
PLEDx = VLEDx × ILEDx
(8)
where x is A, B, C, or D, and VLEDx is the voltage across all
LEDs in the string.
From these equations it can be seen that, if the power in the
A6263 is not limited, then it will increase as the supply voltage
increases but the power in the LEDs will remain constant.
VIN
A6263
(5)
VREG
ILAx
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.
LAx
VIN
IREF
The total current regulator dissipation is the sum of the dissipation in each output regulator. The regulator power for each output
is defined as:
(6)
IINQ
VLED
IREF
VREF
PREGx = (VIN – VLEDx ) × ILEDx
(7)
RREF
GND
where x is 1, 2, 3, or 4.
Note that the voltage drop across the regulator, VREG , is always
greater than the specified minimum drop-out voltage, VDO . The
Figure 4. Internal power dissipation sources.
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A6263
Protected LED Array Driver
Dissipation Limits
There are two features limiting the power that can be dissipated
by the A6263: 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 A6263 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 A6263 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
A6263, 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 temperature of the A6263 increases
above the thermal monitor activation temperature, TJM .
Thermal Dissipation
The amount of heat that can pass from the silicon of the A6263
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A6263. 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
(9)
A thermal resistance from silicon to ambient, RθJA , of approximately 35°C/W can be achieved by mounting the A6263 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 A6263. 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 5, 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 5. Suggested PCB layout for thermal optimization
(maximum available bottom-layer copper recommended)
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A6263
Protected 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)
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A6263
Protected LED Array Driver
Copyright ©2012-2013, 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
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115 Northeast Cutoff
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