The A1569K is a highly integrated solution that combines a
Hall-effect switch with a linear, programmable current regulator,
providing up to 150 mA to drive one or more LEDs. With the
addition of only two passive components and one or more
LEDs, the A1569K forms a complete, magnetically actuated
lighting solution that is small, flexible, elegant, easy to design,
rugged, and reliable. It is optimized for automotive interior and
auxilliary lighting such as map lights, glove boxes, consoles,
vanity mirrors, hood/truck/bed lights, etc.
The LED drive current is set by an external resistor; the LED is
then activated by the built-in Hall-effect switch and features an
adjustable fade-in/fade-out effect. Omnipolar operation (either
north or south pole) and high magnetic sensitivity make the
A1569K tolerant of large air gaps and mechanical misalignment.
System assembly is easier, as the magnet can be oriented with
either pole facing the device. Chopper stabilization provides
low switchpoint drift over the operating temperature range.
The driver can also be activated via an external input for direct
control of the LED.
In addition to contactless operation and safe, constant-current
LED drive, reliability is further enhanced with reverse-battery
protection, thermal foldback, and automatic shutdown for
thermal overload and shorts to ground. The A1569K will prevent
damage to the system by removing LED drive current until
the short is removed and/or the chip temperature has reduced
below the thermal threshold. The driver output is slew-rate-
limited to reduce electrical noise during operation.
A1569K-DS, Rev. 1
MCO-0000611
• Linear LED drive current ≤150 mA set by an external
reference resistor
• High sensitivity, omnipolar Hall-effect switch for LED
on/off control
• Low component count for small size and ease of design
• Elegant fade-in/fade-out effects with adjustable duration
(optional)
• Qualified per AEC-Q100 for automotive applications
• Low dropout voltage and low supply current
• Chopper-stabilized Hall switch
□Low switchpoint drift over temperature
□Insensitivity to physical stress
• Input pin for external LED driver control
• Slew-rate-limited LED output drive for current transient
suppression
• Ruggedness and reliability
□Integrated voltage regulator for operation from 7 to 24 V
□Reverse-battery protection
□Automatic short-circuit and thermal overload
protection and recovery
□–40ºC to 125ºC ambient temperature range
• Small 8-pin SOIC package with thermal pad
Automotive LED Driver with
Integrated Hall-Effect Switch
PACKAGE:
8-Pin SOICN with Exposed Thermal Pad (Su󰀩x LJ)
Typical Application Diagram
A1569K
FEATURES AND BENEFITS DESCRIPTION
Not to scale
VIN
SEN_EN
LA
EXT HALL
IREF
RIREF CFADE
(optional)
THTH
FADE
GND
150 mA
+V
No Connect
or
Connect to GND
LED_ON
Optional
Control Signals
From MCU or
Remote Switch
SLEEP
For standalone operation,
SEN_EN is pulled high
(e.g., tied to VIN)
CBYPASS
Continued on the next page…
February 22, 2019
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
2
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Selection Guide*
Part Number Packing Package Temperature Range, TA (ºC)
A1569KLJTR-T 3000 pieces per 13-in. reel 8-pin SOICN surface mount –40 to 125
* For non-automotive applications, see A1569E datasheet.
Absolute Maximum Ratings
Characteristic Symbol Notes Rating Unit
Forward Supply Voltage VIN (VDD) 30 V
Reverse Supply Voltage VRDD –18 V
Pin SEN_EN VSEN_EN –18 to 30 V
Pin LA VLA –0.3 to 30 V
Pin EXT VEXT –0.3 to 6.5 V
Pin IREF VIREF –0.3 to 6.5 V
Pin THTH VTHTH –0.3 to 6.5 V
Pin FADE VFADE –0.3 to 6.5 V
Operating Ambient Temperature TARange K –40 to 125 ºC
Maximum Junction Temperature TJ(MAX) 165 ºC
Storage Temperature Tstg –65 to 170 ºC
SPECIFICATIONS
RoHS
COMPLIANT
The device is packaged in an 8-pin SOICN (LJ) with an exposed
pad for enhanced thermal dissipation. It is RoHS compliant, with
100% matte-tin leadframe plating.
The A1569K is intented for automotive applications that require
extremely wide operating temperature ranges (up to 125ºC) and
qualification per AEC-Q100. For other applications, refer to the
A1569E.
Description (continued)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
3
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Pinout Drawing and Terminal List
1
2
3
45
6
7
8
PAD
VIN
SEN_EN
EXT
LA
GND
THTH
IREF
FADE
Package LJ, 8-Pin SOICN Pinout Drawing
Terminal List
Pin Number Pin Name Description
1 VIN Supply
2 SEN_EN Hall sensor enable
3 EXT External override input
4 LA LED anode (+) connection
5 FADE Fade-in/fade-out dimming
6 IREF Current reference
7 THTH Thermal threshold
8 GND Ground reference
–PAD Exposed thermal pad (may be left
floating or tied to ground)
Clock/Logic
Sample & Hold
Dynamic Offset
Cancellation
Control Logic
Current
Regulator
Slew
Limit
Thermal
Shutdown
Temp
Monitor
Current Reference
LA
THTHIREF
RIREF
FADE
CFADE
(optional)
EXTSEN_EN
Wake Up
Regulator
VIN
GND
+
RPD RPD
Functional Block Diagram
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
4
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
ELECTRICAL CHARACTERISTICS: Valid at TA = –40°C to 125°C, VIN = 7 to 24 V (unless otherwise specif ied)
Characteristic Symbol Test Conditions Min. Typ.1Max. Units
Electrical Characteristics
VIN Functional Operating Range VIN (VDD)Operating, TJ < 165°C 7 – 24 V
VIN Quiescent Current IINQ LA connected to VIN, LED off – 6 10 mA
VIN Sleep Current IINS SEN_EN and EXT = GND – 10 25 µA
Startup Time tON
SEN_EN = VIN, |B| < |BRPx| – 5 gauss,
RIREF = 600 Ω, CFADE = 100 pF,
measured from VIN > 7 V to ILA source > 90% ILAmax
– – 1 ms
External Response Time tEXT
SEN_EN = GND, VIN > 7 V
RIREF = 600 Ω, CFADE = 100 pF, measured from
EXT > VIH(MIN) to ILA source > 5% ILAmax
– – 1 ms
Current Regulation
Reference Voltage VIREF 267 µA < IREF < 2 mA – 1.2 – V
Reference Current Ratio GH(ILA + 0.5) / IREF – 75 – –
Current Accuracy2EILA 20 mA > ILA > 150 mA –5 ±4 5 %
Output Source Current ILA
SEN_EN = high, BFIELD < BRP – GH × IREF – –
RIREF = 600 Ω, SEN_EN = high and BFIELD < BRP
, or
EXT = high – 150 170 mA
Dropout Voltage VDO
VIN – VLA , ILA = 150 mA – – 2.4 V
VIN – VLA , ILA = 50 mA – 800 – mV
Current Slew Time tFADE(MIN)
Current rising or falling between 10% and 90%,
CFADE = 100 pF – 80 – µs
Logic Inputs
Input Low Voltage VIL SEN_EN, EXT – – 0.8 V
Input High Voltage VIH SEN_EN, EXT 2 – – V
Pull-Down Resistor RPD SEN_EN, EXT – 50 – kΩ
Input Voltage Range VLOGIC
EXT, IREF, THTH, FADE –0.3 – 5.5 V
SEN_EN –0.3 – 24 V
1 Typical data is at TA = 25ºC and VIN = 12 V and it is for design information only.
2 When SEN_EN or EXT = high, EILA = 100 × {[( | ILA | + 0.5 ) × RIREF / 90 ] – 1}, with ILA in mA and RIREF in kΩ.
Continued on next page...
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
5
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Characteristic Symbol Test Conditions Min. Typ.1Max. Units
Protection
Short Detect Voltage VSCD Measured at LA 1.2 – 1.8 V
Short-Circuit Source Current ISCS Short present LA to GND – 1 – mA
Short Release Voltage Hysteresis VSChys
VSCR – VSCD, measured with 0.1 µF cap between
ILA and GN 200 – 500 mV
Thermal Monitor Activation2TJM TJ with ISEN = 90%, THTH open 110 130 145 ºC
Thermal Monitor Slope2dISEN/dTJISEN = 50%, THTH open –3.5 –2.5 –1.5 %/ºC
Thermal Monitor Low Current
Temperature TJL TJ at ISEN = 25%, THTH open 135 150 165 ºC
Overtemperature Shutdown TJF Temperature increasing – 170 – ºC
Overtemperature Hysteresis TJhys Recovery occurs at TJF – TJhys – 15 – ºC
Magnetic Characteristics3
Operate Point BOPS SEN_EN = high and BFIELD > BOP
, LED is off
(EXT = low)
– 40 70 G
BOPN –70 –40 – G
Release Point BRPS SEN_EN = high and BFIELD < BRP
, LED is on
(EXT = low)
5 25 – G
BRPN – –25 –5 G
Hysteresis BHYS | BOPX – BRPX | 5 15 25 G
ELECTRICAL CHARACTERISTICS (continued): Valid at TA = –40°C to 125°C, VIN = 7 to 24 V (unless otherwise
specif ied)
LED On
LED Of
f
Decreasing
BFIELD
Magnitude
Increasing
BFIELD
Magnitude
Decreasing
Magnitude Field
LED Turns On
Increasing
Magnitude Field
LED Turns Off
B
RP
BHYS
B
OP
Figure 1: Hall Switch Control of LED State
1 Typical data is at TA = 25ºC and VIN = 12 V; for design information only.
2 Guaranteed by design.
3 Magnetic flux density, B, is indicated as a negative value for north-polarity magnetic fields, and is a positive value for south-polarity magnetic fields.
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
6
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
THERMAL CHARACTERISTICS
Characteristic Symbol Test Conditions Min. Typ. Max. Units
Thermal Resistance
(Junction to Ambient)
RθJA (High-K)
JEDEC Package MS-012 BA.
Test is performed using a high thermal conductivity,
multilayer printed circuit board that closely
approximates those specified in the JEDEC
standards JESD51-7. Thermal vias are included per
JESD51-5.
– 35 – ºC/W
RθJA (Usual-K)
JEDEC Package MS-012 BA.
Multiple measurement points on both single- and
dual-layer printed circuit boards with minimal
exposed copper (2-oz) area.
See Figure 2 for more detail.
– 62-147 – ºC/W
200
150
100
50
0 0.2 0.4 0.6 0.8
Area of Copper, One Side (in )
2
Package Thermal
Resistance (ºC/W)
One-sided board
Two-sided board
Figure 2: Thermal Resistance (RθJA) versus Copper Area on Printed Circuit Board (PCB)
• All copper is 2 oz. thickness
• Area of copper refers to individual test
locations on PCB
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
7
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
CHARACTERISTIC PERFORMANCE
0
5
10
15
20
25
0 5 10 15 20 25 30
Magnec Hysteresis, BHYSS (gauss)
Supply Voltage, VIN (V)
BHYSS vs. VIN
-40
25
125
TA(°C)
5
7
9
11
13
15
17
19
21
23
25
-50 0 50 100 150
Magnec Hysteresis, BHYSS (gauss)
Ambient Temperature, TA(°C)
BHYSS vs. TA
7
12
18
24
VIN (V)
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Magnec Hysteresis, BOPS (gauss)
Supply Voltage, VIN (V)
BOPS vs. VIN
-40
25
125
T
A
(°C)
0
10
20
30
40
50
60
70
-50 0 50 100 150
Magnec Hysteresis, BOPS (gauss)
Ambient Temperature, TA(°C)
BOPS vs. TA
7
12
18
24
VIN (V)
0
10
20
30
40
50
60
70
0 5 10 15 20 25 30
Magnec Hysteresis, BRPS (gauss)
Supply Voltage, VIN (V)
BRPS vs. VIN
-40
25
125
T
A
(°C)
0
10
20
30
40
50
60
70
-50 0 50 100 150
Magnec Hysteresis, BRPS (gauss)
Ambient Temperature, TA(°C)
BRPS vs. TA
7
12
18
24
VIN (V)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
8
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
-25
-23
-21
-19
-17
-15
-13
-11
-9
-7
-5
0 5 10 15 20 25 30
Magnec Hysteresis, BHYSN (gauss)
Supply Voltage, VIN (V)
BHYSN vs. VIN
-40
25
125
TA(°C)
-25
-23
-21
-19
-17
-15
-13
-11
-9
-7
-5
-50 0 50 100 150
Magnec Hysteresis, BHYSN (gauss)
Ambient Temperature, TA(°C)
BHYSN vs. TA
7
12
18
24
VIN (V)
-70
-60
-50
-40
-30
-20
-10
0
0 5 10 15 20 25 30
Magnec Hysteresis, BOPN (gauss)
Supply Voltage, VIN (V)
BOPN vs. VIN
-40
25
125
T
A
(°C)
-70
-60
-50
-40
-30
-20
-10
0
-50 0 50 100 150
Magnec Hysteresis, BOPN (gauss)
Ambient Temperature, TA(°C)
BOPN vs. TA
7
12
18
24
VIN (V)
-70
-60
-50
-40
-30
-20
-10
0
0 5 10 15 20 25 30
Magnec Hysteresis, BRPN (gauss)
Supply Voltage, VIN (V)
BRPN vs. VIN
-40
25
125
T
A
(°C)
-70
-60
-50
-40
-30
-20
-10
0
-50 0 50 100 150
Magnec Hysteresis, BRPN (gauss)
Ambient Temperature, TA(°C)
BRPN vs. TA
7
12
18
24
VIN (V)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
9
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
0
1
2
3
4
5
6
7
8
9
10
0 5 10 15 20 25 30
Quiescent Current, IINQ (mA)
Supply Voltage, VIN (V)
IINQ vs. VIN
-40
25
125
T
A
(°C)
0
1
2
3
4
5
6
7
8
9
10
-50 0 50 100 150
Quiescent Current, IINQ (mA)
Ambient Temperature, TA(°C)
IINQ vs. TA
7
12
18
24
VIN (V)
0
5
10
15
20
25
0 5 10 15 20 25 30
Sleep Current, IINS (µA)
Supply Voltage, VIN (V)
IINS vs. VIN
-40
25
125
T
A
(°C)
0
5
10
15
20
25
-50 0 50 100 150
Sleep Current, IINS (µA)
Ambient Temperature, TA(°C)
IINS vs. TA
7
12
18
24
VIN (V)
60
65
70
75
80
85
90
0 5 10 15 20 25 30
Reference Current Rao, GH
Supply Voltage, VIN (V)
GHvs. VIN (IREF = 2 mA)
-40
25
125
T
A
(°C)
60
65
70
75
80
85
90
-50 0 50 100 150
Reference Current Rao, GH
Ambient Temperature, TA(°C)
GHvs. TA (IREF = 2 mA)
7
12
18
24
VIN (V)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
10
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
100
110
120
130
140
150
160
170
180
0 5 10 15 20 25 30
Output Source Current, ILA (mA)
Supply Voltage, VIN (V)
ILA vs. VIN
-40
25
125
T
A
(°C)
100
110
120
130
140
150
160
170
180
-50 0 50 100 150
Output Source Current, ILA (mA)
Ambient Temperature, TA(°C)
ILA vs. TA
7
12
18
24
VIN (V)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
11
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Function Truth Table
EXT SEN_EN Magnetic Field B LED
0 0 X OFF
0 1 B > BOP OFF
0 1 B < BRP ON
1 X X ON
Example Function Diagrams
B > BOP
B < BRP
High
High
Max
Low
Low
0 mA
Fade in Fade out
BFIELD
ILED
SEN_EN
EXT
Figure 3: Hall-Activated Operation
With EXT low and SEN_EN high, the switching of the LED is controlled by the BFIELD as detected by the Hall sensor.
B > BOP
B < BRP
High
High
Max
Low
Low
0 mA
BFIELD
ILED
SEN_EN
EXT
Figure 4: Disabling the Hall Sensor with SEN_EN
The Hall sensor can be disabled by driving SEN_EN low. This will force the LED off even if the BFIELD is below BOP
.
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
12
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
B > BOP
B < BRP
High
High
Max
Low
Low
0 mA
BFIELD
ILED
SEN_EN
EXT
Don’t Care
Don’t Care Don’t Care
Figure 5: Overriding the Hall Sensor with EXT
When EXT is driven high, it doesn’t matter what the state of the SEN_EN input or the BFIELD are, the LED will be on.
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
13
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
FUNCTIONAL DESCRIPTION
The A1569K is a linear current regulator with an integrated Hall-
effect switch designed to provide drive current and protection for
a string of series-connected high brightness LEDs in automotive
applications. It provides a single programmable current output
at up to 150 mA, with low minimum dropout voltages below the
main supply voltage.
The A1569K is specifically designed for use in illumination
applications where the LED activity is controlled by the inte-
grated Hall-effect switch or an external logic signal, or both.
Current regulation is maintained and the LEDs are protected
during a short to ground at any point in the LED string. A short
to ground on the output terminal will disable the output until the
short is removed. 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 regulator. 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. This pin should be connected
directly to the negative supply.
SEN_EN
Logic input to enable the Hall-effect switch. When this pin is
enabled (logic high), the output current can be controlled by the
state of the magnetic field on the Hall sensor. If the magnetic
field is below BRP, then the LED current will be on, and if the
magnetic field is above BOP, then the LED current will be off.
EXT
Logic input to enable LED current output which provides a direct
on/off action. Note, if the LED is on because the SEN_IN pin is
enabled and the magnetic field is below BRP, then it will remain
on regardless of EXT.
FADE
A capacitor between this pin and GND controls the turn-on and
turn-off times of the LED current.
Note: For best performance, it is important that the ground return
for CFADE is as short as possible, that it is made directly to the
ground pin of the IC, and that it is not shared with other circuitry
or carry other ground return currents (Kelvin connection).
IREF
A 1.2 V reference used to set the LED current drive. Connect
resistor RIREF to GND to set the reference current.
Note: Do not place any capacitance across the RIREF resistor.
THTH
When floating, the thermal monitor threshold TJM is enabled and
the output current will start to reduce with increasing temperature
above 130°C. Connecting the THTH pin directly to GND will
disable the thermal monitor function; however, the thermal shut-
down feature will continue to function—it cannot be disabled.
Refer to the Temperature Monitor section below for more detail.
LA
Current source connected to the anode of the first LED in the
string.
PAD
This is an isolated pad for thermal dissipation only. This pad is
isolated and can be connected to ground or left floating.
LED Current Level
The LED current is controlled by a linear current regulator
between the VIN pin and the LA output. The basic equation that
determines the nominal output current at this pin is:
Given SEN_EN = high and BFIELD < BRP
, or EXT = high,
where ILA is in A, RIREF is in Ω, VREF = 1.2 V, and GH = 75.
Note: the output current may be reduced from the set level by the
thermal monitor circuit.
I=
LA
V
REF
× G
H
R
IREF
(1
)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
14
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Conversely, the reference resistor may be calculated from:
where ILA is in A, RIREF is in Ω, VREF = 1.2 V, and GH = 75.
For example, where the required current is 75 mA, the resistor
value will be:
It is important to note that because the A1569K is a linear regula-
tor, the maximum regulated current is limited by the power dissi-
pation and the thermal management in the application. All current
calculations assume an adequate heat sink, or airflow, or both, for
the power dissipated. Thermal management is at least as impor-
tant 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 applica-
tion section below provides further detail on thermal management
and the associated limitations.
Sleep Mode
When SEN_EN and EXT are held low, the A1569K 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.
Fade-In/Fade-Out
Fade timing is controlled by external capacitor CFADE on the
FADE pin. A larger capacitor will result in a longer fade time.
The 10%-90% fade time is approximated by the equation:
tFADE = CFADE × 0.8 × 106 (4)
where tFADE is in seconds and CFADE is in farads.
Therefore, CFADE of 1 µF will result in tFADE of approximately
1 second (tFADE = 0.000001 F × 0.8 × 106 = 0.8 seconds).
Fade-in is triggered when:
• EXT goes high, or
• SEN_EN is high and BFIELD goes below BRP , or
• BFIELD is below BRP and SEN_EN goes high.
Fade-out is triggered when:
• SEN_EN is low or BFIELD is above BOP and EXT goes low, or
• EXT is low and BFIELD is above BOP and SEN_EN goes low, or
• EXT is low and SEN_EN is high and BFIELD goes above BOP
.
Safety Features
The circuit includes several features to ensure safe operation and
to protect the LEDs and the A1569K:
• The current regulator between VIN and LA output provide a
natural current limit due to the regulation.
• The LA 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 as in Figure 6 will not
result in a short fault condition. The current through the remain-
ing LEDs will remain in regulation and the LEDs will be pro-
tected. If the LA output is pulled below the short detect voltage
as in Figure 7, it will disable the regulator on the 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 LA rises
above the short detect voltage, the regulator will be re-enabled.
A shorted LED or LEDs, as in Figure 8, will not result in a short
fault condition. The current through the remaining LEDs will
remain in regulation and the LEDs will be protected.
Temperature Monitor and Thermal Protection
The temperature monitor function, included in the A1569K,
reduces the LED current as the silicon junction temperature of the
A1569K increases (see Figure 9). By mounting the A1569K on
the same thermal substrate as the LEDs, this feature can also be
VIN
LA
GND
A1569K
Current remains regulated
in non-shorted LEDs.
Figure 6: Any Cathode Short to Ground
R
=
IREF
90
0.075 + 0.0005 (3)
= 1192 Ω or 1.19 kΩ
R
=
IREF I
LA
+ 0.5 (2
)
V
REF
× G
H
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
15
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
used to limit the dissipation of the LEDs. As the junction tem-
perature of the A1569K increases, the regulated current level is
reduced, reducing the dissipated power in the A1569K 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 tem-
perature reaches the overtemperature shutdown threshold tempera-
ture (TJF).
In extreme cases, if the chip temperature exceeds the overtem-
perature limit (TJF), the regulator will be disabled. The tem-
perature will continue to be monitored and the regulator will be
re-activated when the temperature drops below the threshold
provided by the specified hysteresis. Note that it is possible for
the A1569K 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 too close to the shut-
down temperature. The period of oscillation will depend on TJM,
the dissipated power, the thermal mass of any heat sink present,
and the ambient temperature.
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.
When THTH is tied to ground, the thermal monitor function is
disabled; however, the overtemperature thermal protection will
continue to function—it cannot be disabled.
VIN
LA
GND
A1569K
Shorted output is
disabled. Low current
is sourced to detect
when short is cleared.
Figure 7: Output Short to Ground
VIN
LA
GND
A1569K
Only shorted LED(s)
is(are) inactive. Current
remains regulated in
non-shorted LED(s).
Figure 8: Shorted LED(s)
100
90
80
60
40
20
25
070 90 110 130 150 170
TJM
TJF
TJL
Junction Temperature, T (ºC)
J
Relative Sense Current (%)
Figure 9: Temperature Monitor Current Reduction
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
16
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
APPLICATION INFORMATION
Power Dissipation
The most critical design consideration when using a linear regula-
tor such as the A1569K is 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 A1569K:
• 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 it is not related to the regulated
current. The quiescent power (PQ) is therefore defined as:
PQ = VIN × IINQ (5)
REFERENCE POWER
The reference circuit draws the reference current from the supply
and passes it through the reference resistor to ground. The refer-
ence 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:
REGULATOR POWER
In most application circuits, the largest dissipation will be pro-
duced by the output current regulator. The power dissipated the
current regulator is simply the product of the output current and
the voltage drop across the regulator. The regulator power the
output is defined as:
PREG = (VIN – VLED
) × ILED (7)
Note that the voltage drop across the regulator (VREG) is always
greater than the specified minimum dropout 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 A1569K is the sum of the quiescent power, the
reference power, and the power in the regulator:
PD = PQ + PREG – PREF (8)
The power that is dissipated in the LEDs is:
PLED = VLED × ILED (9)
where VLED is the voltage across all LEDs in the string.
From these equations (and as illustrated in Figure 10), it can be
seen that, if the power in the A1569K is not limited, then it will
increase as the supply voltage increases while the power in the
LEDs will remain constant.
Dissipation Limits
There are two features limiting the power that can be dissipated
by the A1569K: 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 A1569K
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, 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 A1569K is switched off. The period of this thermal shutdown
cycle will depend on several electrical, mechanical, and thermal
parameters.
THERMAL FOLDBACK
If RθJA is low enough, then the thermal foldback feature will have
time to act. This will limit the silicon temperature by reducing the
regulated current and therefore the dissipation.
The thermal monitor will reduce the LED current as the tempera-
ture of the A1569K increases above the thermal monitor activa-
tion temperature (TJM), as shown in Figure 11. The figure shows
the operation of the A1569K with a string of two white LEDs
running at 150 mA. The forward voltage of each LED is 3.15 V,
and the graph shows the current as the supply voltage increases
from 15 to 18 V. As the supply voltage increases, without the
thermal foldback feature, the current would remain at 150 mA, as
shown by the dashed line. The solid line shows the resulting cur-
rent 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 A1569K in order to limit the temperature increase,
as shown in Figure 12. The figure shows the operation of the
A1569K under the same conditions as Figure 11, that is, a string
of two white LEDs running at 150 mA, with each LED forward
voltage at 3.15 V. The graph shows the temperature as the supply
voltage increases from 15 to 18 V. Without the thermal foldback
PREF =
(V –V V
IN REFREF
) ×
R
IREF
(6)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
17
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
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.
Figure 11 and Figure 12 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 avail-
able supply voltage can vary over a two-to-one range, or greater
when double battery or load dump conditions are taken into con-
sideration. In such systems, is it necessary to design the applica-
tion circuit such that the system meets the required performance
targets over a specified voltage range.
To determine this range when using the A1569K, 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 dropout 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).
VLED is constant for a given current and does not vary with sup-
ply voltage. Therefore, VREG provides the variable difference
between VLED and VIN. VREG has a minimum value below which
2.5
2.0
1.5
1.0
0.5
010 11 12 13 14 15 16 17
18
Supply Voltage, (V)VIN
Power Dissipation, P (W)
D
2 LED in series:
I= 150 mA
LED
V= 6.3 V
LED
LED Power
Figure 10: Power Dissipation versus Supply Voltage
150
148
146
144
142
140
18.0 18.5 19.0 19.5 20.0 20.5 21.0
Supply Voltage, (V)VIN
LED Current, (mA)ILA
2 LED in series:
I= 150 mA
LED
TA= 50ºC
V= 6.3 V
LED
Without Thermal Monitor
154
152
Figure 11: LED Current versus Supply Voltage
135
130
125
120
115
18.0 18.5 19.0 19.5 20.0 20.5 21.0
Supply Voltage, (V)V
IN
Junction Temperature, (ºC)T
J
2 LED in series:
I= 150 mA
LED
T
A
= 50ºC
V= 6.3 V
LED
Without Thermal Monitor
145
140
Figure 12: Junction Temperature versus Supply Voltage
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
18
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
the regulator can no longer be guaranteed to maintain the output
current within the specified accuracy. This level is defined as the
regulator dropout 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 dropout voltage (VDO) and the forward volt-
age 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) (10)
As an example, consider the configuration used in Figure 11,
namely a string of two white LEDs, running at 150 mA, with
each LED forward voltage at 3.15 V. The minimum supply volt-
age will be approximately:
VIN(MIN) = 0.8 + (2 × 3.15) = 7.1 V (11)
Maximum Supply Limit: Thermal Limitation
As described above, when the thermal monitor reaches the activa-
tion temperature (TJM), due to increased power dissipation as the
supply voltage rises, the thermal foldback feature causes the out-
put 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
A1569K reaches TJM.
Note that, if the thermal monitor circuit is disabled (by connect-
ing the THTH pin to GND), then the maximum supply limit will
be the specified maximum continuous operating temperature,
150°C.
The maximum power dissipation is therefore defined as:
where ΔT(MAX) is the difference between the thermal monitor
activation temperature (TJM) of the A1569K and the maximum
ambient temperature (TA(max)), and RθJA is the thermal resistance
from the internal junctions in the silicon to the ambient environ-
ment. If minimum LED current is not a critical factor, then the
maximum voltage is simply the maximum specified in the param-
eter tables above.
Thermal Dissipation
The amount of heat that can pass from the silicon of the A1569K
to the surrounding ambient environment depends on the thermal
resistance of the structures connected to the A1569K. 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 (13)
A thermal resistance from silicon to ambient (RθJA) of approxi-
mately 35°C/W can be achieved by using a high thermal conduc-
tivity, multilayer printed circuit board as specified in the JEDEC
standards JESD51-7 for JEDEC Package MS-012 BA (including
thermal vias as called out in JESD51-5). Additional improve-
ments may be achieved by optimizing the PCB design.
Optimizing Thermal Layout
The features of the printed circuit board, including heat conduc-
tion and adjacent thermal sources such as other components, have
a significant effect on the thermal performance of the device. To
optimize thermal performance, the following should be taken into
account:
• Maximizing the forward voltage of the LEDs relative to the
VIN of the A1569K will greatly reduce the power dissipated in
the A1569K by reducing the voltage drop across the A1569K.
• The A1569K exposed thermal pad should be connected to as
much copper area as is available. This copper area may be left
floating or connected to ground if desired.
• 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 13, has the greatest effect.
• Additional exposed copper area on the opposite side of the
board should be connected by means of thermal vias. The
copper should cover as much area as possible.
• Other thermal sources should be placed as far away from the
device as possible.
PD(MAX) =R
JA
T(MAX)
(12)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
19
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Signal Traces
LJ Package
Exposed
Thermal Pad
Top Layer
Exposed
Copper
Ø 0.3 mm Via
LJ Package
Outline
0.7 mm
0.7 mm
Figure 13: Suggested PCB Layout for Thermal Optimization
(Maximum available bottom-layer copper recommended)
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
20
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Package Outline Drawing
(Reference MS-012BA)
Dimensions in millimeters – NOT TO SCALE
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
3.30
2
1
8
C
1.27
5.60
2.41
1.75
0.65
2.41 NOM
3.30 NOM
C
1.27 BSC
B
D
2
1
8
C
SEATING
PLANE
C0.10
8X
0.25 BSC
1.04 REF
1.70 MAX
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°
A
Branded Face
SEATING PLANE
GAUGE PLANE
PCB Layout Reference View
A
B
C
D
Terminal #1 mark area
Exposed thermal pad (bottom surface)
Hall element (E1) centered in package (not to scale).
Reference land pattern layout (reference IPC7351 SOIC127P600X175-9AM);
all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to
on a multilayer PCB, thermal vias at the exposed thermal pad land can improve
thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
E1
Figure 14: Package LJ, 8-Pin SOICN with Exposed Thermal Pad
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
21
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
For the latest version of this document, visit our website:
www.allegromicro.com
Revision History
Revision Revision Date Description of Revision
– December 11, 2015 Initial release
1 February 22, 2019 Minor editorial updates
Copyright ©2019, Allegro MicroSystems, LLC
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permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
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