A6262 Datasheet

A6262
Automotive LED Array Driver
Features and Benefits
Description
▪AEC Q-100 qualified
▪Total LED drive current up to 400 mA
▪Current shared equally up to 100 mA by 4 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 A6262 is a linear, programmable current regulator providing
up to 100 mA from each of four 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 4 strings at 100 mA each. Outputs can be
connected in parallel or left unused as required.
Applications:
▪Dome light, map light, space lighting, mood lighting
Short detection is provided to protect the LEDs and the A6262
during a short-to-ground at any LED output pin. The output
will automatically resume the regulated current when the short
is removed.
Packages
10-pin MSOP with
exposed thermal pad
(suffix LY)
A temperature monitor is included to reduce the LED drive
current if the chip temperature exceeds an adjustable thermal
threshold.
16-pin TSSOP with
exposed thermal pad
(suffix LP)
The device packages are a 10-pin MSOP (suffix LY), and
a 16-pin TSSOP (LP), both with exposed pad for enhanced
thermal dissipation. They are lead (Pb) free, with 100% matte
tin leadframe plating.
Not to scale
+
Typical Application Diagram
Automotive
12 V power net
VIN
A6262
PWM dimming
input from LCU
On/Off
EN
LA1
SW
LA2
IREF
LA3
THTH
LA4
PAD
GND
–
A6262-DS, Rev. 7
100 mA
100 mA
100 mA
100 mA
A6262
Automotive LED Array Driver
Selection Guide
Part Number
Ambient Operating
Temperature, TA (°C)
A6262KLPTR-T
A6262KLYTR-T
–40 to 125
Packing
Package
4000 pieces per 13-in. reel
16-pin TSSOP with exposed thermal pad,
4.4 × 5 mm case
10-pin MSOP with exposed thermal pad,
3 × 3 mm case
Absolute Maximum Ratings1
Characteristic
Rating
Unit
–0.3 to 50
V
Pin EN
–0.3 to 50
V
Pins LA[1:4]
–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
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 information
Characteristic
Symbol
Test Conditions*
LP package
Package Thermal Resistance
(Junction to Ambient)
RθJA
LY package
Package Thermal Resistance
(Junction to Pad)
Value
Unit
On 4-layer PCB based on JEDEC standard
34
ºC/W
On 2-layer PCB with 3.8 in.2 of copper area each side
43
ºC/W
On 4-layer PCB based on JEDEC standard
48
ºC/W
48
ºC/W
2
ºC/W
On 2-layer PCB with
2.5 in.2
RθJP
of copper area each side
*To be verified by characterization. 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
A6262
Automotive LED Array Driver
Functional Block Diagram
VBAT
VIN
D
SW
IREF
RTH
R
Q
Current
Regulators
Control
Logic
EN
THTH
C
Deglitch
Q
Temp
Comp
Temp
Monitor
LA1
LA2
Slew
Limit
LA3
LA4
Current
Reference
RREF
PAD
Pin-out Diagrams
NC 1
16 NC
NC 2
15 NC
THTH 3
14 SW
IREF 4
GND 5
PAD
13 EN
12 VIN
GND
Terminal List Table
Number
Name
LP
LY
Function
EN
13
9
Enable
SW
14
10
Switch input
LA1 6
11 LA4
GND
5
3
Ground reference
LA2 7
10 LA3
NC 8
9 NC
IREF
4
2
Current reference
LA1
6
4
LED anode (+) connection 1
LA2
7
5
LED anode (+) connection 2
LA3
10
6
LED anode (+) connection 3
LA4
11
7
LED anode (+) connection 4
NC
1,2,8,
9,15,16
n.a.
PAD
–
–
Exposed thermal pad
THTH
3
1
Thermal threshold
VIN
12
8
Supply
LP Package
THTH 1
10 SW
IREF 2
9 EN
GND 3
PAD
8 VIN
LA1 4
7 LA4
LA2 5
6 LA3
LY Package
No connection; connect to GND
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115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
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A6262
Automotive LED Array Driver
ELECTRICAL CHARACTERISTICS1 Valid at TJ = –40°C to 150°C, VIN = 7 to 40 ; unless otherwise noted
Characteristics
Symbol
Test Conditions
Min.
Typ.
Max.
Unit
Supply and Reference
VIN Functional Operating Range2
6
–
50
V
–
–
10
mA
–
15
µA
15
30
µs
VIN Quiescent Current
IINQ
LA[1:4] connected to VIN
VIN Sleep Current
IINS
EN = GND, VIN = 16 V
–
Startup Time
tON
VIN > 7 V to ILA1 < –5 mA, RREF = 125 Ω
5
Current Regulation
Reference Voltage
Reference Current Ratio
Current Accuracy3
Current Matching4
Output Current, High Level
Maximum Output Current
Minimum Drop-out Voltage
VIREF
1.15
1.2
1.25
V
ILAx / IREF
–
12.5
–
–
EILAx
–10 mA > ILAx > –100 mA
–5
±4
5
%
EIMLAx
–20 mA > ILAx > –100 mA,
VLAx match to within 1 V
–
5
10
%
EN = high
–
GH ×
IREF
–
–
–105
–100
–95
mA
IREF = 9.2 mA, EN = high
–
–
–110
mA
VIN – VLAx , ILAx = –100 mA
–
–
800
mV
VIN – VLAx , ILAx = –40 mA
–
–
660
mV
Current rising or falling between 10% and 90%
50
80
110
µs
GH
ILAx
ILAxmax
VDO
Current Slew Time
0.7 mA < IREF < 8.8 mA
IREF = 8 mA, EN = high
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
–2
–0.8
–0.5
mA
VSCR
Measured at LAx
–
–
1.9
V
200
–
500
mV
Short Release Voltage
Short Release Voltage Hysteresis
Thermal Monitor Activation Temperature
VSChys
TJM
VSCR – VSCD
95
115
130
°C
ISEN = 50%, THTH open
–3.5
–2.5
–1.5
%/°C
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
Thermal Monitor Slope
Thermal Monitor Low Current
Temperature
dISEN/dTJ
TJ with ISEN = 90%, THTH open
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).
3When EN = high, E
ILAx = 100 × [( | ILAx | × RREF / 15 ) –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.
2Function
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115 Northeast Cutoff
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A6262
Automotive LED Array Driver
Functional Description
The A6262 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 four 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.
The A6262 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. The
EN input overrides the SW input when EN is high. When EN
transitions from high to low, SW input logic is reset to off.
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.
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 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
RREF
where ILAx is in mA and RREF is in kΩ; K is 15.
(1)
The output current may be reduced from the set level by the thermal monitor circuit.
Conversely the reference resistors may be calculated from:
RREF =
K
ILAx
where ILAx is in mA and RREF is in kΩ.
(2)
For example, where the required current is 90 mA for all four
channels the resistor value will be:
RREF = 15
90
= 167 Ω
It is important to note that because the A6262 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 A6262 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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A6262
Sleep Mode
When EN is held low the A6262 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 A6262:
•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 A6262 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 A6262 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.
Temperature Monitor A temperature monitor function,
included in the A6262, reduces the LED current as the silicon
junction temperature of the A6262 increases (see figure 2). By
mounting the A6262 on the same thermal substrate as the LEDs,
this feature can also be used to limit the dissipation of the LEDs.
Automotive LED Array Driver
VIN
A. Any LED cathode short to ground.
Current remains regulated in
non-shorted LEDs. Matching may be
affected.
A6262
LA1
LA2
LA3
LA4
GND
VIN
A6262
B. Any LAx output short to ground.
Shorted output is disabled. Other
outputs remain active.
LA1
LA2
LA3
LA4
GND
VIN
A6262
C. Current remains regulated.
Matching may be affected.
Only the shorted LED is inactive.
LA1
LA2
LA3
LA4
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.
A6262
LA1
LA2
LA3
LA4
GND
Figure 1. Short circuit conditions.
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A6262
90
80
60
TJM
40
25
20
0
70
130
90
110
Junction Temperature, TJ (°C)
TJM will increase as the voltage at the THTH pin, VTHTH , is
reduced and is defined as approximately:
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.
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 A6262 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.
150
170
Figure 2. Temperature monitor current reduction.
1.3
250
1.2
200
RTH pull-up
to 5 V
150
RTH (kΩ)
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.
TJF
TJL
100
1.0
VTHTH
50
0
70
1.1
RTH pull-down
to GND
0.9
RTH pull-up
to 3 V
80
VTHTH (V)
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 (%)
As the junction temperature of the A6262 increases, the regulated
current level is reduced, reducing the dissipated power in the
A6262 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.
Automotive 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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A6262
Automotive LED Array Driver
Application Information
Power Dissipation
The most critical design considerations when using a linear regulator such as the A6262 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 A6262:
The total power dissipated in the A6262 is the sum of the quiescent power, the reference power, and the power in each of the our
regulators:
•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 therefore defined as:
PQ = VIN × IINQ(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
RREF
The total current regulator dissipation is the sum of the dissipation in each output regulator. The regulator power for each output
is defined as:
where x is 1, 2, 3, or 4.
PDIS = PQ + PREF
+ PREGA + PREGB + PREGC + PREGD
The power that is dissipated in each string of LEDs is:
PLEDx = VLEDx × ILEDx
where x is A, B, C, or D, and VLEDx is the voltage across all
LEDs in the string.
(7)
(8)
VIN
A6262
VREG
ILAx
LAx
(5)
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.
PREGx = (VIN – VLEDx ) × ILEDx
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 .
VIN
IREF
IINQ
VLED
IREF
VREF
RREF
GND
(6)
Figure 4. Internal power dissipation sources.
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A6262
Automotive LED Array Driver
Dissipation Limits
There are two features limiting the power that can be dissipated
by the A6262: 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 A6262 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 A6262 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
A6262, 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 A6262 with 4 strings of 3 red LEDs, each string
running at 50 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 50 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 A6262 in order to limit the temperature increase, as shown
in figure 7. The figure shows the operation of the A6262 under
the same conditions as figure 6. That is, 4 strings of 3 red LEDs,
each string running at 50 mA with each LED forward voltage at
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 A6262 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 A6262 increases above the thermal monitor activation
temperature, TJM , as shown in figure 6. The figure shows the
With thermal monitor
4 Strings
VLED = 6.9 V
ILED = 50 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
130
2.5
125
2.0
120
TJ (°C)
Power Dissipation, PD (W)
3.0
1.5
LED Power
1.0
A6262 Power
0.5
0
8
9
10
Figure 5. Power Dissipation versus Supply Voltage
14
15
115
Without thermal monitor
With thermal monitor
110
4 Strings
VLED = 6.9 V
ILED = 50 mA
12
13
11
Supply Voltage, VIN (V)
4 Strings
VLED = 6.9 V
ILED = 50 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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A6262
Automotive LED Array Driver
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.
Thermal Dissipation
The amount of heat that can pass from the silicon of the A6262
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A6262. 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
•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
sum of the minimum drop-out voltage, VDO , and the forward
voltage of the LEDs in the string, VLED . The supply voltage must
(9)
A thermal resistance from silicon to ambient, RθJA , of approximately 30°C/W (LP package) or 34°C/W (LY package) can be
achieved by mounting the A6262 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 A6262. Multiple
thermal vias, as shown in figure 8, help to conduct the heat from
the exposed pad of the A6262 to the copper on each side of the
board. The thermal resistance can be reduced by using a metal
substrate or by adding a heatsink.
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 A6262 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.
Figure 8. Board via layout for thermal dissipation: (top) LP
package and (bottom) LY package.
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A6262
Automotive LED Array Driver
always be greater than this value and the minimum specified supply voltage, that is:
VIN > VDO + VLED, and
VIN > VIN (min) (10)
As an example, consider the configuration used in figures 6 and
7 above, namely 4 strings of 3 red LEDs, each string running at
50 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
A6262 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
(11)
where ΔT(max) is difference between the thermal monitor activation temperature, TJM , of the A6262 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.
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 A6262 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. In addition, in all cases when EN is high, the EN input
will override the SW toggle status and enable the outputs. At the
high-to-low transition of EN, the SW toggle will always be reset
to the off state.
When power is applied, 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, where a manual
switch may be used to turn the light on and the lighting control
unit may dim the light to off (see figure 10). In these cases it is
important to understand the interaction of the two control inputs.
•In all cases, when EN is high the EN input will override the SW
toggle status and enable the outputs.
•When EN is low the SW input can be used to toggle the outputs
on and off.
•The only time there is any interaction between the EN input and
the SW toggle is the high-to-low transition of EN, where the
SW toggle will always be reset to the off state.
•The SW toggle will also be reset to the off state at power-up.
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11
A6262
Automotive LED Array Driver
+
+
12 V PWM
high-side drive
Automotive
24 V power net
VIN
VIN
A6262
EN
LA1
EN
SW
IREF
On/Off
LA2
A6262
LA1
LA2
LA3
LA4
SW
LA3
IREF
LA4
THTH
THTH
GND
GND
–
–
A. High brightness (HB) LED incandescent lamp replacement
B. Higher voltage operation
+
Automotive
12 V power net
VIN
A6262
On/Off
EN
LA1
SW
LA2
IREF
LA3
LA4
THTH
GND
–
C. Mix of output combinations
Figure 9. Typical applications with various supply and output options.
+
Automotive
24 V power net
VIN
PWM dimming
input from LCU
A6262
EN
LA1
On/Off
SW
LA2
IREF
LA3
LA4
THTH
GND
–
Figure 10. Typical applications using SW and EN together
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12
A6262
Automotive LED Array Driver
Package LP, 16-Pin TSSOP with Exposed Thermal Pad
0.45
5.00±0.10
16
0.65
16
8º
0º
0.20
0.09
1.70
B
3±0.05
4.40±0.10
3.00
6.40±0.20
6.10
0.60 ±0.15
A
1
1.00 REF
2
3±0.05
0.25 BSC
Branded Face
16X
SEATING
PLANE
0.10 C
0.30
0.19
SEATING PLANE
GAUGE PLANE
C
3.00
C
PCB Layout Reference View
For Reference Only; not for tooling use (reference MO-153 ABT)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
1.20 MAX
0.65 BSC
1 2
0.15
0.00
A Terminal #1 mark area
B
Exposed thermal pad (bottom surface); dimensions may vary with device
C Reference land pattern layout (reference IPC7351
SOP65P640X110-17M);
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
13
A6262
Automotive LED Array Driver
Package LY, 10-Pin MSOP with Exposed Thermal Pad
3.00 ±0.10
0° to 6°
10
0.15 ±0.05
3.00 ±0.10
4.88 ±0.20
A
0.53 ±0.10
1
2
0.25
1.98
1
Seating Plane
Gauge Plane
2
B
For Reference Only; not for tooling use (reference JEDEC MO-187)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
1.73
A Terminal #1 mark area
B Exposed thermal pad (bottom surface)
10
0.86 ±0.05
SEATING
PLANE
0.27
0.18
0.50
REF
0.05
0.15
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115 Northeast Cutoff
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14
A6262
Automotive LED Array Driver
Revision History
Revision
Revision Date
Description of Revision
6
June 24, 2013
Update Features List, figure 5
7
June 25, 2015
Temperature Monitor text on page 7 updated to match EC table: derating slope is -2.5% per °C
Copyright ©2009-2015, 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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15
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