A1569K
Automotive LED Driver with
Integrated Hall-Effect Switch
FEATURES AND BENEFITS
DESCRIPTION
• 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
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-ratelimited to reduce electrical noise during operation.
PACKAGE:
8-Pin SOICN with Exposed Thermal Pad (Suffix LJ)
Continued on the next page…
Not to scale
For standalone operation,
SEN_EN is pulled high
(e.g., tied to VIN)
Optional
Control Signals
From MCU or
Remote Switch
RIREF
+V
CBYPASS
VIN
SLEEP
LA
150 mA
SEN_EN
LED_ON
EXT
No Connect
or
Connect to GND
HALL
IREF
FADE
THTH
GND
CFADE
(optional)
Typical Application Diagram
A1569K-DS
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
Description (continued)
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.
Selection Guide*
Part Number
Packing
A1569KLJTR-T
3000 pieces per 13-in. reel
* For non-automotive applications, see A1569E datasheet.
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.
Package
8-pin SOICN surface mount
Temperature Range, TA (ºC)
–40 to 125
RoHS
COMPLIANT
SPECIFICATIONS
Absolute Maximum Ratings
Characteristic
Symbol
Notes
Rating
Unit
Forward Supply Voltage
VIN (VDD)
30
V
Reverse Supply Voltage
VRDD
–18
V
VSEN_EN
–18 to 30
V
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
Pin SEN_EN
Pin LA
–0.3 to 6.5
V
–40 to 125
ºC
Operating Ambient Temperature
TA
Maximum Junction Temperature
TJ(MAX)
165
ºC
Tstg
–65 to 170
ºC
Storage Temperature
Range K
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
Automotive LED Driver with
Integrated Hall-Effect Switch
Current Reference
Sample & Hold
Dynamic Offset
Cancellation
A1569K
Slew
Limit
GND
LA
Temp
Monitor
Control Logic
Clock/Logic
Regulator
Thermal
Shutdown
Current
Regulator
Wake Up
RPD
VIN
SEN_EN
RPD
EXT
FADE
IREF
THTH
+
CFADE
RIREF
(optional)
Functional Block Diagram
Pinout Drawing and Terminal List
Terminal List
VIN
1
8
GND
SEN_EN
2
7
THTH
EXT
3
6
IREF
LA
4
5
FADE
PAD
Package LJ, 8-Pin SOICN Pinout Drawing
Pin Number
Pin Name
Description
1
VIN
2
SEN_EN
3
EXT
4
LA
LED anode (+) connection
5
FADE
Fade-in/fade-out dimming
6
IREF
Current reference
Supply
Hall sensor enable
External override input
7
THTH
Thermal threshold
8
GND
Ground reference
–
PAD
Exposed thermal pad (may be left
floating or tied to ground)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
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.1
Max.
Units
Electrical Characteristics
VIN Functional Operating Range
Operating, TJ < 165°C
7
–
24
V
VIN Quiescent Current
VIN (VDD)
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 Accuracy2
EILA
20 mA > ILA > 150 mA
–5
±4
5
%
SEN_EN = high, BFIELD < BRP
–
GH × IREF
–
–
RIREF = 600 Ω, SEN_EN = high and BFIELD < BRP, or
EXT = high
–
150
170
mA
VIN – VLA , ILA = 150 mA
–
–
2.4
V
VIN – VLA , ILA = 50 mA
–
800
–
mV
Current rising or falling between 10% and 90%,
CFADE = 100 pF
–
80
–
µs
Output Source Current
Dropout Voltage
Current Slew Time
ILA
VDO
tFADE(MIN)
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
Input Voltage Range
VLOGIC
–
50
–
kΩ
EXT, IREF, THTH, FADE
–0.3
–
5.5
V
SEN_EN
–0.3
–
24
V
Continued on next page...
1
2
Typical data is at TA = 25ºC and VIN = 12 V and it is for design information only.
When SEN_EN or EXT = high, EILA = 100 × {[( | ILA | + 0.5 ) × RIREF / 90 ] – 1}, with ILA in mA and RIREF in kΩ.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
ELECTRICAL CHARACTERISTICS (continued): Valid at TA = –40°C to 125°C, VIN = 7 to 24 V (unless otherwise
specif ied)
Characteristic
Symbol
Test Conditions
Min.
Typ.1
Max.
Units
1.2
–
1.8
V
–
1
–
mA
200
–
500
mV
Protection
Short Detect Voltage
VSCD
Measured at LA
Short-Circuit Source Current
ISCS
Short present LA to GND
Short Release Voltage Hysteresis
Thermal Monitor Activation2
Thermal Monitor Slope2
VSCR – VSCD, measured with 0.1 µF cap between
ILA and GN
VSChys
TJM
dISEN/dTJ
TJ with ISEN = 90%, THTH open
110
130
145
ºC
ISEN = 50%, THTH open
–3.5
–2.5
–1.5
%/ºC
135
150
165
ºC
Thermal Monitor Low Current
Temperature
TJL
TJ at ISEN = 25%, THTH open
Overtemperature Shutdown
TJF
Temperature increasing
–
170
–
ºC
Overtemperature Hysteresis
TJhys
Recovery occurs at TJF – TJhys
–
15
–
ºC
BOPS
SEN_EN = high and BFIELD > BOP, LED is off
(EXT = low)
–
40
70
G
–70
–40
–
G
Magnetic Characteristics3
Operate Point
Release Point
Hysteresis
BOPN
BRPS
SEN_EN = high and BFIELD < BRP, LED is on
(EXT = low)
5
25
–
G
BRPN
–
–25
–5
G
BHYS
| BOPX – BRPX |
5
15
25
G
BHYS
BOP
Decreasing
BFIELD
Magnitude
BRP
Decreasing
Magnitude Field
LED Turns On
LED Off
Increasing
Magnitude Field
LED Turns Off
LED On
Increasing
BFIELD
Magnitude
Figure 1: Hall Switch Control of LED State
Typical data is at TA = 25ºC and VIN = 12 V; for design information only.
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.
1
2
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
THERMAL CHARACTERISTICS
Characteristic
Symbol
Min.
Typ.
Max.
Units
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.
Test Conditions
–
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
Thermal Resistance
(Junction to Ambient)
Package Thermal
Resistance (ºC/W)
200
One-sided board
Two-sided board
150
• All copper is 2 oz. thickness
• Area of copper refers to individual test
locations on PCB
100
50
0
0.2
0.4
0.6
2
Area of Copper, One Side (in )
0.8
Figure 2: Thermal Resistance (RθJA) versus Copper Area on Printed Circuit Board (PCB)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
CHARACTERISTIC PERFORMANCE
BHYSS vs. TA
25
20
15
10
TA (°C)
-40
25
125
5
0
0
5
10
15
20
25
30
Magnetic Hysteresis, BHYSS (gauss)
Magnetic Hysteresis, BHYSS (gauss)
BHYSS vs. VIN
25
23
21
19
17
15
13
11
9
7
5
VIN (V)
7
12
18
24
-50
Supply Voltage, VIN (V)
0
50
40
30
TA (°C)
20
-40
25
125
10
0
15
20
25
30
Magnetic Hysteresis, BOPS (gauss)
Magnetic Hysteresis, BOPS (gauss)
60
10
70
60
50
40
VIN (V)
30
7
12
18
24
20
10
0
-50
Supply Voltage, VIN (V)
0
60
-40
25
125
50
40
30
20
10
0
15
20
Supply Voltage, VIN (V)
25
30
Magnetic Hysteresis, BRPS (gauss)
Magnetic Hysteresis, BRPS (gauss)
TA (°C)
10
100
150
BRPS vs. TA
70
5
50
Ambient Temperature, TA (°C)
BRPS vs. VIN
0
150
BOPS vs. TA
70
5
100
Ambient Temperature, TA (°C)
BOPS vs. VIN
0
50
70
VIN (V)
60
7
12
18
24
50
40
30
20
10
0
-50
0
50
100
150
Ambient Temperature, TA (°C)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
BHYSN vs. TA
-5
-7
-9
-11
-13
-15
-17
-19
-21
-23
-25
TA (°C)
-40
25
125
0
5
10
15
20
25
30
Magnetic Hysteresis, BHYSN (gauss)
Magnetic Hysteresis, BHYSN (gauss)
BHYSN vs. VIN
-5
-7
-9
-11
-13
-15
-17
-19
-21
-23
-25
VIN (V)
7
12
18
24
-50
Supply Voltage, VIN (V)
0
-20
-30
-40
TA (°C)
-50
-40
25
125
-60
-70
15
20
25
30
Magnetic Hysteresis, BOPN (gauss)
Magnetic Hysteresis, BOPN (gauss)
-10
10
0
-10
-20
-30
VIN (V)
-40
7
12
18
24
-50
-60
-70
-50
Supply Voltage, VIN (V)
0
-20
-30
-40
TA (°C)
-50
-40
25
125
-60
-70
15
20
Supply Voltage, VIN (V)
25
30
Magnetic Hysteresis, BRPN (gauss)
Magnetic Hysteresis, BRPN (gauss)
-10
10
100
150
BRPN vs. TA
0
5
50
Ambient Temperature, TA (°C)
BRPN vs. VIN
0
150
BOPN vs. TA
0
5
100
Ambient Temperature, TA (°C)
BOPN vs. VIN
0
50
0
-10
-20
-30
VIN (V)
-40
7
12
18
24
-50
-60
-70
-50
0
50
100
150
Ambient Temperature, TA (°C)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
IINQ vs. TA
10
9
8
7
6
5
4
3
2
1
0
TA (°C)
-40
25
125
0
5
10
15
20
25
Quiescent Current, IINQ (mA)
Quiescent Current, IINQ (mA)
IINQ vs. VIN
10
9
8
7
6
5
4
3
2
1
0
30
VIN (V)
7
12
18
24
-50
Supply Voltage, VIN (V)
0
IINS vs. VIN
25
TA (°C)
20
-40
25
125
15
10
5
Sleep Current, IINS (µA)
Sleep Current, IINS (µA)
100
150
IINS vs. TA
25
0
VIN (V)
7
12
18
24
20
15
10
5
0
0
5
10
15
20
25
30
-50
Supply Voltage, VIN (V)
80
75
70
65
60
10
15
20
Supply Voltage, VIN (V)
25
30
Reference Current Ratio, GH
-40
25
125
5
100
90
TA (°C)
0
50
150
GH vs. TA (IREF = 2 mA)
90
85
0
Ambient Temperature, TA (°C)
GH vs. VIN (IREF = 2 mA)
Reference Current Ratio, GH
50
Ambient Temperature, TA (°C)
VIN (V)
85
7
12
18
24
80
75
70
65
60
-50
0
50
100
150
Ambient Temperature, TA (°C)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
ILA vs. TA
180
170
160
150
140
130
TA (°C)
-40
25
125
120
110
100
0
5
10
15
20
Supply Voltage, VIN (V)
25
30
Output Source Current, ILA (mA)
Output Source Current, ILA (mA)
ILA vs. VIN
180
170
160
150
140
VIN (V)
7
12
18
24
130
120
110
100
-50
0
50
100
150
Ambient Temperature, TA (°C)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
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
BFIELD
B > BOP
B < BRP
SEN_EN
High
Low
EXT
High
Low
ILED
Max
0 mA
Fade in
Fade out
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.
BFIELD
B > BOP
B < BRP
SEN_EN
High
Low
EXT
High
Low
ILED
Max
0 mA
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.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
BFIELD
B > BOP
B < BRP
SEN_EN
High
Low
EXT
High
Low
ILED
Max
0 mA
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.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
FUNCTIONAL DESCRIPTION
The A1569K is a linear current regulator with an integrated Halleffect 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 integrated 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 shutdown 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,
VREF × GH
ILA =
RIREF
(1)
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.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
Conversely, the reference resistor may be calculated from:
VREF × GH
RIREF =
ILA + 0.5
Safety Features
(2)
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:
RIREF =
90
= 1192 Ω or 1.19 kΩ
0.075 + 0.0005
(3)
It is important to note that because the A1569K 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 an adequate heat sink, or airflow, or both, for
the power dissipated. 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.
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
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.
A short to ground on any LED cathode as in Figure 6 will not
result in a short fault condition. The current through the remaining LEDs will remain in regulation and the LEDs will be protected. 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.
Fade-In/Fade-Out
Temperature Monitor and Thermal Protection
Sleep Mode
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).
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
Current remains regulated
in non-shorted LEDs.
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.
LA
A1569K
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 .
GND
Figure 6: Any Cathode Short to Ground
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Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
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 shutdown temperature. The period of oscillation will depend on TJM,
the dissipated power, the thermal mass of any heat sink present,
and the ambient temperature.
In extreme cases, if the chip temperature exceeds the overtemperature limit (TJF), the regulator will be disabled. The tem-
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.
VIN
LA
Shorted output is
disabled. Low current
is sourced to detect
when short is cleared.
A1569K
GND
Figure 7: Output Short to Ground
Relative Sense Current (%)
used to limit the dissipation of the LEDs. As the junction temperature 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 temperature reaches the overtemperature shutdown threshold temperature (TJF).
100
90
80
TJM
60
40
TJF
25
20
0
70
TJL
90
110
130
150
170
Junction Temperature, TJ (ºC)
Figure 9: Temperature Monitor Current Reduction
VIN
LA
A1569K
Only shorted LED(s)
is(are) inactive. Current
remains regulated in
non-shorted LED(s).
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.
GND
Figure 8: Shorted LED(s)
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Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
APPLICATION INFORMATION
Power Dissipation
The most critical design consideration when using a linear regulator 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:
THERMAL SHUTDOWN
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 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:
(V – VREF ) × VREF
(6)
PREF = IN
RIREF
REGULATOR POWER
In most application circuits, the largest dissipation will be produced 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.
Dissipation Limits
There are two features limiting the power that can be dissipated
by the A1569K: thermal shutdown and thermal foldback.
• The quiescent power to run the control circuits
• The power in the reference circuit
• The power due to the regulator voltage drop
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.
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 temperature of the A1569K increases above the thermal monitor activation 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 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 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
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Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
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.
Power Dissipation, PD (W)
2.5
2.0
2 LED in series:
VLED = 6.3 V
ILED = 150 mA
11
12
13
14
15
16
17
18
Supply Voltage, VIN (V)
Figure 10: Power Dissipation versus Supply Voltage
154
LED Current, ILA (mA)
130
2 LED in series:
VLED = 6.3 V
ILED = 150 mA
TA = 50ºC
125
120
18.5
19.0
19.5
20.0
20.5
21.0
Supply Voltage Limits
0.5
152
Without Thermal Monitor
150
148
146
140
18.0
135
Figure 12: Junction Temperature versus Supply Voltage
LED Power
142
m
her
tT
hou
t
i
W
o
al M
Supply Voltage, VIN (V)
1.0
144
or
nit
140
115
18.0
1.5
0
10
145
Junction Temperature, TJ (ºC)
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.
19.0
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
2 LED in series:
VLED = 6.3 V
ILED = 150 mA
TA = 50ºC
18.5
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.
19.5
20.0
20.5
Supply Voltage, VIN (V)
Figure 11: LED Current versus Supply Voltage
21.0
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 supply voltage. Therefore, VREG provides the variable difference
between VLED and VIN. VREG has a minimum value below which
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Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
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 voltage of the LEDs in the string (VLED). The supply voltage must
always be greater than this value and the minimum specified
supply voltage, that is:
VIN > VDO + VLED and VIN > VIN(MIN)
(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 voltage 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 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
A1569K 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:
T(MAX)
PD(MAX) =
RJA
(12)
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 environment. If minimum LED current is not a critical factor, then the
maximum voltage is simply the maximum specified in the parameter 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 approximately 35°C/W can be achieved by using a high thermal conductivity, 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 improvements may be achieved by optimizing the PCB design.
Optimizing Thermal Layout
The features of the printed circuit board, including heat conduction and adjacent thermal sources such as other components, have
a 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.
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Automotive LED Driver with
Integrated Hall-Effect Switch
A1569K
Signal Traces
LJ Package
Outline
LJ Package
Exposed
Thermal Pad
Top Layer
Exposed
Copper
0.7 mm
Ø 0.3 mm Via
0.7 mm
Figure 13: Suggested PCB Layout for Thermal Optimization
(Maximum available bottom-layer copper recommended)
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Automotive LED Driver with
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A1569K
Package Outline Drawing
For Reference Only – Not for Tooling Use
(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
4.90 ±0.10
1.27
0.65
8°
0°
3.30 NOM
8
8
1.75
0.25
0.17
D E1
B
2.41 NOM 3.90 ±0.10 6.00 ±0.20
2.41 5.60
A
1.04 REF
1
2
1
1.27
0.40
0.25 BSC
Branded Face
C
8X
0.10
C
0.51
0.31
1.27 BSC
1.70 MAX
0.15
0.00
SEATING
PLANE
2
3.30
C
PCB Layout Reference View
SEATING PLANE
GAUGE PLANE
A Terminal #1 mark area
B Exposed thermal pad (bottom surface)
C Reference land pattern layout (reference IPC7351 SOIC127P600X175-9AM);
all pads a minimum of 0.20 mm from all adjacent pads; adjust as necessary to
meet application process requirements and PCB layout tolerances; when mounting
on a multilayer PCB, thermal vias at the exposed thermal pad land can improve
thermal dissipation (reference EIA/JEDEC Standard JESD51-5)
D Hall element (E1) centered in package (not to scale).
Figure 14: Package LJ, 8-Pin SOICN with Exposed Thermal Pad
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Automotive LED Driver with
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A1569K
Revision History
Revision
Revision Date
–
December 11, 2015
Description of Revision
Initial release
Copyright ©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 any devices or systems, including but not limited to life support devices or systems, in which a failure of
Allegro’s product can reasonably be expected to cause bodily harm.
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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