Description
The A6260 is a linear, programmable current regulator
providing up to 350 mA for driving high-brightness LEDs.
The LED current, accurate to 4%, is set by a single low-power
sense resistor. Driving LEDs with constant current ensures
safe operation with maximum possible light output.
For automotive applications, optimum performance is
achieved when driving between 1 and 3 LEDs at cur-
rents up to 350 mA.
The low dropout voltage of the A6260 allows a single white
LED to be driven safely, at full current, with a supply voltage
down to 6 V.
An enable input allows PWM dimming and can be used to
enable low-current sleep mode. The rate of change of current
during PWM switching is limited to reduce EMI.
Overcurrent detection is provided to protect the LEDs and
the A6260 during short-to-supply or short-to-ground at any
LED terminal.
The integrated temperature monitor can be used to reduce
the LED drive current if the chip temperature exceeds the
thermal limit.
The device is available in an 8-pin SOIC package with exposed
thermal pad (suffix LJ). The device is lead (Pb) free with 100%
matte-tin leadframe plating.
6260-DS, Rev. 4
Features and Benefits
▪ Automotive grade
▪ LED drive current up to 350 mA
▪ 6 to 40 V supply
▪ Reverse battery protection
▪ Low drop-out voltage
▪ LED short circuit and thermal protection
▪ 10 μA maximum shutdown current
▪ PWM dimming control input
▪ Current slew rate limiting
High Brightness LED Current Regulator
Package: 8-pin SOIC with exposed
thermal pad (suffix LJ)
Typical Application
Not to scale
A6260
7 to 20 V
(–14 V min, 40 V max)
L
A
PWM Dimming
and
On-Off Control
EN
VIN
SENSE
GND
Automotive
12 V Power Net
THTH LC
LSS
A6260
High Brightness LED Current Regulator
A6260
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Selection Guide
Part Number Packing Ambient Temperature, TA
(°C)
A6260KLJTR-T 3000 pieces per reel –40 to 125
A6260SLJTR-T 3000 pieces per reel –20 to 85
THERMAL CHARACTERISTICS may require derating at maximum conditions
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance
RθJA
4-layer PCB based on JEDEC standard 35 ºC/W
2-layer PCB with 0.8 in.2 of copper area
each side 62 ºC/W
RθJP 2 ºC/W
*Additional thermal information available on Allegro website.
Absolute Maximum Ratings*
Characteristic Symbol Notes Rating Units
Load Supply Voltage VIN –14 to 40 V
EN Pin Voltage VEN –14 to 40 V
LA and LC Pins Voltage VLx –0.3 to 40 V
LSS Pin Voltage VLSS –0.3 to 0.3 V
SENSE Pin Voltage VSENSE –0.3 to 0.3 V
THTH Pin Voltage VTHTH –0.3 to 7 V
Ambient Operating Temperature Range TA
Range K –40 to 125 ºC
Range S –20 to 85 ºC
Junction Operating Temperature Range TJ–40 to 150 ºC
Storage Temperature Range Tstg –55 to 150 ºC
ESD Rating, Human Body Model AEC-Q100-002, all pins 2000 V
ESD Rating, Charged Device Model AEC-Q100-011, all pins 1050 V
*With respect to GND.
High Brightness LED Current Regulator
A6260
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Block Diagram
LA
VIN
SENSE
Reg
GND
Reference
Generator
EN
VBATT
RS
Current
Regulator
Current Limited
Switch
Slew
Limit
LSS
Output
Monitor
Temp
Monitor
Temp
Comp LC
Control
Logic
THTH
RTH
Terminal List Table
Number Name Description
1 SENSE Current sense input
2 GND Ground reference
3 THTH Thermal threshold input
4 EN Enable input
5 VIN Main supply
6 LA LED anode (+) connection
7 LC LED cathode (-) connection
8 LSS Low-side sense connection
8
7
6
5
1
2
3
4
LSS
LC
LA
VIN
SENSE
GND
THTH
EN
Pin-out Diagram
High Brightness LED Current Regulator
A6260
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristics Symbol Test Conditions Min. Typ. Max. Units
Supply and Reference
VIN Functional Operating Range1VIN 6 – 40 V
VIN Quiescent Current I
INQ LA, LC unconnected – – 4 mA
VIN Shutdown Current IINS EN < 400 mV – 1 10 μA
Startup Time tON EN 2 V to 35 mA ILC 91827μs
Current Regulation
Maximum Current Sink ILCmax RS = 250 mΩ, VIN – VLA > 2 V 350 – – mA
Current Sink ILC RS = 286 mΩ, VIN – VLA > 2 V 333 350 367 mA
Current Sink Accuracy errILC 100 mA < ILC < 350 mA –5 ±4 5 %
SENSE Reference Voltage VSENREF 260 mΩ < RS < 1Ω 97 102 107 mV
Switch Dropout Voltage VDO
VIN – VLA , ILOAD = 350 mA – 2.25 2.35 V
VIN – VLA , ILOAD = 150 mA – 1.35 1.4 V
Regulator Saturation Voltage VSAT
VLC – VSENSE, ILOAD = 350 mA – 500 550 mV
VLC – VSENSE, ILOAD = 150 mA – 250 275 mV
Output Current Slew Time trCurrent rising from 10% to 90% 50 80 120 μs
tfCurrent falling from 90% to 10% 60 100 150 μs
Logic Input
Input Low Voltage VIL – – 0.8 V
Input High Voltage VIH 2––V
Input Hysteresis VIhys 150 350 – mV
Protection
Switch Overcurrent Trip Level I
LAOC –600 –500 –400 mA
Overcurrent Detection Time2tOCD From detection to ISCU > –1.2 mA – 3 – μs
Switch Current Limit ILALIM –1.5×
ILAOC –mA
LC Short Circuit Release Voltage VSCCR Measured at VLC, when rising 1.0 1.2 1.4 V
Short Circuit Source Current2ISCU When short is detected –1.5 –1.1 –0.7 mA
Thermal Monitor Activation Temperature TJM TJ at ILC = 90%, THTH open 90 105 120 ºC
Thermal Monitor Low Current Temperature TJL TJ at ILC = 25%, THTH open 110 130 150 ºC
Overtemperature Shutdown Threshold TJF Temperature increasing – 165 – ºC
Overtemperature Hysteresis TJhys Recovery = TJF – TJhys –15–ºC
1Functions correctly, but parameters are not guaranteed, below the general limit (7 V).
2For input and output current specifications, negative current is defined as coming out of (sourcing) the specified device pin.
ELECTRICAL CHARACTERISTICS valid at TJ = –40°C to 150°C, VIN = 7 to 40 V, unless noted otherwise
High Brightness LED Current Regulator
A6260
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
The A6260 is a linear current regulator that is designed to provide
drive current and protection for series-connected, high bright-
ness LEDs in automotive applications. It provides programmable
current output at load voltages up to 3 V below the main supply
voltage. For automotive applications optimum performance is
achieved when driving 1 to 3 LEDs at currents up to 350 mA.
The LED current is set by a single low-power sense resistor and
the LED brightness can be further controlled by a PWM input to
the EN pin. The EN input can also be used as an on/off switched
input and the A6260 will enter a low current (<10 μA) sleep
mode if EN is held low.
For incandescent replacement configurations, the EN input can
be connected directly to the VIN pin with the supply to VIN con-
trolled by a simple on/off switch.
The LEDs and the regulator are protected from excessive currents
caused by short circuits to ground or supply or by reversal of the
power supply connections.
Integrated thermal management circuits can be used to reduce
the regulated current level at high temperatures to limit power
dissipation.
Pin Functions
VIN Pin Supply to the control circuit. A small-value ceramic
bypass capacitor (typically 100 nF) should be connected from
close to this pin to the GND pin.
GND Pin Ground reference connection. Should be connected
directly to the negative supply as close as possible to the bottom
(ground connection) of the sense resistor.
EN Pin Logic input to enable operation. Can be used as a direct
PWM input. Chip enters a low-power sleep mode when this pin is
held low.
THTH Pin Sets the thermal monitor threshold, TJM, where the
output current starts to be reduced with increasing temperature.
When this pin is left open, the threshold temperature will typi-
cally be the specified default value. A resistor connected between
THTH and GND can be used to increase the threshold tempera-
ture. A resistor connected between THTH and VIN can be used to
decrease the threshold temperature. Connecting THTH directly to
GND disables the thermal monitor function.
LA Pin Switched and protected current source connected to the
anode of the LEDs.
LC Pin Controlled current sink connected to the cathode of the
LEDs.
LSS Pin Low-side current sink connection from the current regu-
lator to power ground via a sense resistor. A current sense resistor
(240 mΩ to 3 Ω) is connected between LSS and power ground.
SENSE Pin LED current sense input. The high impedance
SENSE input should have an independent connection to the top
(LSS connection side) of the sense resistor.
LED Current Level
The LED current is controlled by the internal current regulator
between the LC and LSS pins. This current, defined as the current
into the LC pin, ILC, is set by the value, RS
, of the sense resis-
tor. The voltage across the sense resistor, measured between the
SENSE pin and the GND pin, is compared to a reference voltage,
nominally 102 mV, allowing the use of a low-value sense resistor
with low power dissipation.
The LED current is thus defined as:
I
LC = VSENREF / RS (1)
conversely:
R
S = VSENREF / ILC
The nominal output current settings, ILC, versus the current
setting resistor values, RS, are given in the following table. The
current level defined here is the 100% current level before any
current reduction effects due to the temperature monitor,
described later in this document.
Sense Resistor Selection
ILC
(mA)
RS
(mΩ)
PD(RS)
(mW)
ILC
(mA)
RS
(mΩ)
PD(RS)
(mW)
350 286 35 125 800 13
300 333 30 100 1000 10
250 400 25 70 1429 7
200 500 20 50 2000 5
150 667 15 35 2857 4
Parallel operation
The A6260 is a constant current controller, that is, it controls the
output current irrespective of output voltage (within the compli-
ance range). This allows the outputs of two or more A6260s to be
connected in parallel (see figure 4e, in the Applications Infor-
mation section). In this configuration, each A6260 must have a
Functional Description
High Brightness LED Current Regulator
A6260
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
dedicated sense resistor, which determines its share of the current
provided to the LED.
LED Brightness
Although the LED brightness can be controlled by changing the
current (intensity) this may slightly affect the color or the color
temperature of the light from the LED. When multiple LEDs
are used, it is usually more desirable to control the brightness by
switching the fixed LED current with a pulse width modulated
signal. This allows the LED brightness to be set using a digital
control input with little effect on the LED color.
In the A6260, the brightness level can be controlled by a PWM
signal applied to the EN input. This controls both the low-side
linear regulator and the high-side switch.
When EN is switched from high to low, the low-side regulator
reduces the current to zero before allowing the high-side switch
to turn off.
When EN is switched from low to high, the high-side switch is
turned on before the low-side regulator increases the current to
the full operating level.
To assist EMC, the rate of change of the LED current is limited
and the current will rise and fall within the limits (tr, tf) defined in
the Electrical Characteristics table.
Note that EN can be used for PWM dimming even when the
high-side switch is bypassed. (See figure 4(d)).
Sleep Mode
When EN is held low, the A6260 will be in shutdown mode and
all internal circuits will be in a low-power sleep mode. In this
mode, the input current, IINS
, will be 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 A6260:
▪ The high-side switch between VIN and LA has overcurrent
detection and a current limiter. It assumes that a short circuit is
present if the current exceeds the trip value, ILAOC
, for longer
than the overcurrent detection time, tOCD.
▪ The current regulator between LC and LSS provides a natural
current limit due to the regulation.
▪ 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 total of five short circuit conditions can exist as illustrated in
figure 1.
LA Short to Supply (figure 1a) This condition is permitted
because the current remains regulated by the current sink. This
configuration may also be used in applications with low supply
voltages (see figure 4d in the Applications Information section).
LA Short to Ground (figure 1b) This condition is detected when
the high-side switch current exceeds the trip value, ILAOC
, for
longer than the overcurrent detection time, tOCD (3 μs typical).
When a short is detected, the switch and the regulator are both
disabled. When the voltage at LC drops below the short release
voltage, VSCCR, a low value current, ISCU (1.1 mA typical), is
then sourced from LA to provide a short circuit monitor. When
(a) LA Short to Supply
Permitted because
current remains
regulated
(b) LA Short to Ground
Detected when switch
current exceeds trip
value for longer than
3 μs, released when
VLC >VSCCR
Detected when switch
current exceeds trip
value for longer than
3 μs, released when
VLC >VSCCR
(c) LC Short to Supply
Current remains
regulated, thermal
shutdown provides
protection
Current remains
regulated, thermal
shutdown provides
protection
(d) LC Short to Ground (e) LA Short to LC
L
A
LC
VIN
A6260
GND
L
A
LC
VIN
A6260
GND
L
A
LC
VIN
A6260
GND
L
A
LC
VIN
A6260
GND
L
A
LC
VIN
A6260
GND
Figure 1. Short circuit conditions detected
High Brightness LED Current Regulator
A6260
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
the short circuit is removed the short circuit source current, ISCU ,
pulls the voltage at the LC pin above VSCCR, and the switch and
regulator are re-enabled.
LC Short to Supply (figure 1c) In this condition, the current
into the LC pin remains regulated but the power dissipated in
the A6260 increases. This higher dissipation causes the thermal
monitor to reduce the current to protect the regulator. In extreme
cases, or in cases where the thermal monitor is disabled, the
increased dissipation may cause temperature to reach the thermal
shutdown level, at which point the regulator will be disabled.
LC Short to Ground (figure 1d) This condition is detected when
the high-side switch current exceeds the trip value, ILAOC
, for
longer than the overcurrent detection time, tOCD (3 μs typical).
When a short is detected, the switch and the regulator are both
disabled. When the voltage at LC drops below the short release
voltage, VSCCR, a low value current, ISCU (1.1 mA typical), is
then sourced from LA to provide a short circuit monitor. When
the short circuit is removed, ISCU pulls the voltage at the LC pin
above VSCCR, and the switch and regulator are re-enabled.
LA Short to LC (figure 1e) This condition is effectively the same
as the LC Short-to-Supply condition. In this condition, the cur-
rent into the LC pin remains regulated but the power dissipated in
the A6260 increases. This higher dissipation causes the thermal
monitor to reduce the current to protect the regulator. In extreme
cases, or in cases where the thermal monitor is disabled, the
increased dissipation may cause temperature to reach the thermal
shutdown level, at which point the regulator will be disabled.
Temperature Monitor
The primary function of the temperature monitor included in the
A6260 is to limit the power dissipation of the A6260 and maintain
the junction temperature below the maximum. However, it can
also be used to reduce LED current as LED temperature increases.
This can be achieved by mounting the A6260 on the same thermal
substrate as the LEDs, so that temperature rise in the LEDs would
also affect the A6260. As the junction temperature of the A6260
increases, the integrated temperature monitor lowers the regulated
current level, reducing the dissipated power in the A6260 and in the
LEDs. As shown in figure 2, from the full 100% current level (see
the LED Current Level section), current is reduced at a rate of 4%
per degree Celsius typically, until the point at which the current drops
to 25% of the full level. The junction temperature at the 25% current
level is defined as TJL. If the temperature continues to rise above
TJL, the temperature monitor would continue to reduce current, but
at a slower rate, until the temperature reaches the overtemperature
shutdown 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 typically 98°C. The thermal monitor activation temperature,
TJM, is defined in the Electrical Characteristics table at the 90%
current level.
TJM can be increased by reducing the voltage at the THTH pin,
VTHTH, and is defined as approximately:
003630V5031
TTHTH
JM .
.−
=
(2)
where TJM is in °C.
The equivalent circuit of the THTH pin is a 1.124 V source with
a series 5 kΩ resistor. A resistor connected between THTH and
GND will reduce VTHTH and increase TJM , according to the fol-
lowing formula:
TH
TH
THTH
R
R
V+
×= 5
124.1
(3)
where RTH, in kΩ, is the resistor between THTH and GND.
A resistor connected between THTH and a reference supply
greater than 2 V will increase VTHTH and reduce TJM. For
0
20
25
40
60
80
90
T
JM
T
JF
T
JL
100
70 90 110 130 150 170
Junction Temperature, TJ (°C)
Relat ive LED Current, ILC (%)
Figure 2. Temperature monitor current reduction
High Brightness LED Current Regulator
A6260
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
example, with RTH connected to 5 V, VTHTH will be:
()
TH
RTHTH
R55
1241V1241V+
×−+= ..
(4)
Figure 3 shows how the nominal value of the thermal monitor
activation temperature varies with the voltage at THTH and with
a pull-down resistor, RTH, to GND or with a pull-up resistor, RTH,
to 5V.
In extreme cases, if the chip temperature exceeds the overtem-
perature limit, TJF, both the sink regulator and the source switch
will be disabled. The temperature will continue to be monitored
and the output re-activated when the temperature drops below the
threshold provided by the specified hysteresis, TJhys.
0
50
100
150
200
250
300
50 70 90 110 130 150
T
JM
(°C)
R
TH
(kΩ)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
V
THTH
(V)
RTH pull-up to 5 V
VTHTH
RTH pull-down to GND
Figure 3. TJM versus RTH (pull-up or –down), and VTHTH
High Brightness LED Current Regulator
A6260
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Applications Information
L
A
EN
VIN
Automotive
12V Power Net
High-Side
PWM Source
SENSE
GND
LC
Ground
LSS
THTH
LA
SENSE
GND
EN
VIN
Automotive
12V Power Net
LC
Ground
LSS
THTH
LA
EN
VIN
Automotive
12 V Power Net
SENSE
GND
LC
Ground
LSS
THTH
L
A
EN
VIN
Low Voltage
(>6V) Supply
SENSE
GND
LC
Ground
LSS
THTH
L
A
SENSE
GND
EN
VIN
Automotive
12 V Power Net
LC
Ground
LSS
THTH
GND
EN
VIN
THTH
SENSE
LC
LSS
LA
PWM Dimming
and
On-Off Control
PWM Dimming
and
On-Off Control
Figure 4. Typical applications circuits
(a) Basic circuit with PWM (b) Switched supply plus high-side PWM source
(c) Simple switched supply (lamp replacement) (d) Low voltage operation
(e) Parallel operation for higher LED current
High Brightness LED Current Regulator
A6260
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Copyright ©2007-2009, Allegro MicroSystems, Inc.
The products described here are manufactured under one or more U.S. patents or U.S. patents pending.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, 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 in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment 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
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); dimensions may vary with device
A
Branded Face
