The A8522 is a programmable multi-output LED driver for
LCD backlighting. It integrates a current-mode boost converter
with internal power switch and 8 current sinks. The IC operates
from 4.5 to 36 V, and is able to withstand up to 40 V load-dump
conditions encountered in automotive systems.
The control loop is optimized to eliminate night flash in display
backlight applications.
The I2C interface allows the user to set the LED currents
individually, up to 60 mA per LED channel. Adjacent channels
may be combined to drive higher-current LED strings. The
PWM dimming duty cycle also is independently controlled
for each LED channel. This flexibility makes the A8522 a
single solution for a wide range of LED applications. Two-way
communication allows fault status to be reported.
A8522-DS, Rev. 12
MCO-0000141
• AEC-Q100 qualified
• Wide input voltage range of 4.5 to 36 V
• Operates down to 3.9 V (VIN falling) for idle stop, and up
to 40 V for load dump
• Integrated boost converter with DMOS switch and OVP
protection up to 39 V
• 8 fully integrated LED current sinks, with individually
programmable current up to 60 mA per channel
• I2C™ interface for programming LED current, PWM
dimming, and various protection thresholds per channel
• Ability to drive multiple loads from a single IC
• Extensive PWM dimming (up to 10,000:1 at 100 Hz),
individually programmable for each channel
• Extensive diagnostics and fault reporting
• Thermal warning and derating of LED current at higher
temperatures
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
PACKAGE:
Typical Application Drawing
Not to scale
A8522
Continued on the next page…
Continued on the next page…
APPLICATIONS:
Automotive:
• Infotainment
• Cluster
• Center-stack lighting
• Head-up display (HUD)
• Daytime running lights (DRL)
COUT
CVDD
OVP
Q1
L1
INS
VDD LED1
LED2
PAD
LED8
R
FSET
R
ADDR
C
Z
R
Z
GATE
EN
FLAG
V
IN
(4.5 to 36 V)
SW
COMP
PGND
AGND
FSET/SYNC
CIN CQ1
V
C
V
C
SDA
SCL
ADDR
A8522
D1
Optional
VOUT
External
Synchronization
R
SENSE
VIN
GPO1 GPO2
Status
/
Interrupt
I
2
C Interface
A
A
A
B
BExternal pull-up voltage, or
connected to VDD
GND C
P
FEATURES AND BENEFITS DESCRIPTION
July 2, 2018
28-pin TSSOP with exposed thermal pad
(suffix LP)
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
2
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
PWM dimming duty cycle also is independently controlled for each
LED channel. This flexibility makes the A8522 a single solution
for a wide range of LED applications, in some cases offering the
ability to replace two or more LED driver ICs with a single device.
The A8522 detects and protects against a wide variety of fault
conditions, and two-way communication allows fault status to be
reported. It provides protection against output short and overvoltage,
open or shorted diode, open or shorted LED pin, shorted boost
switch or inductor, and IC overtemperature. A dual cycle-by-cycle
current limit protects the internal switch against switch overcurrent.
If required, the IC can drive an external PFET as an input-disconnect
switch that is triggered by integrated current sense.
• Buffered PWM dimming control for all channels to facilitate
localized dimming applications
• Polyphase PWM dimming: LED currents staggered to reduce
light flickering and input ripple current
• Synchronize boost switching frequency: 400 kHz to 2.3 MHz
to allow operation below or above the AM band
• Programmable frequency dithering to reduce EMI
• Typical LED current accuracy of 0.7%, and LED-to-LED
matching accuracy of 0.8%
• Protection features
□Open/shorted LED pin detection
□Programmable LED string short detection
□Open/shorted external components (including boost
inductor, Schottky diode, FSET resistor and so forth)
□Input overcurrent protection against output to GND short
□Cycle-by-cycle switch current limit
□Overtemperature, and output overvoltage and undervoltage
protection
FEATURES AND BENEFITS (continued) DESCRIPTION (continued)
SELECTION GUIDE
Part Number
Operating Ambient
Temperature Range
TA (°C)
Package Packing [1] Leadframe
Plating
A8522KLPTR-T –40 to 125 28-pin TSSOP with exposed
thermal pad 4000 pieces per 13-in. reel 100% matte tin
[1] Contact Allegro™ for additional packing options.
Table of Contents
Features and Benefits 1
Description 1
Applications 1
Package 1
Typical Application Drawing 1
Selection Guide 2
Specifications 3
Absolute Maximum Ratings 3
Thermal Characteristics 3
Functional Block Diagram 4
Pinout Diagram and Terminal List Table 5
Electrical Characteristics 6
Characteristic Performance 9
Fault Handling 14
Input Overcurrent Protection 14
Switch Overcurrent Protection 15
LED String Open Fault Detection 15
Protection Against Open/Missing BOOST Diode 16
Functional Description 17
Enabling the IC 17
PWM Dimming 18
Output Current and Voltage 18
Boost Frequency Dithering 22
Polyphase Grouping 22
Boost Output Voltage Regulation 23
Output Hysteresis 24
Soft Start Timing 24
Input Disconnect Switch 24
System Failure Detection and Protection 26
Fault Handling 27
Application Information 30
Package Outline Design 37
Appendix A: Programming Information A-1
I2C Interface Description A-2
Timing Considerations A-2
I2C Command Write to the A8522 A-3
I2C Command Read from the A8522 A-4
Order of Reading and Writing Registers A-4
Dealing with Incomplete Transmission A-4
Register Map A-6
Register Field Reference A-8
Appendix B: Feedback Loop Calculations B-1
Power Stage Transfer Function B-1
Output to Control Transfer Function B-2
Stabilizing the Closed Loop System B-4
Measuring Feedback Loop Gain, Phase Margin B-6
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
3
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
ABSOLUTE MAXIMUM RATINGS [1]
Characteristic Symbol Notes Rating Unit
LEDx Pins VLEDx –0.3 to 42 V
¯
F
¯
¯
L
¯
¯
A
¯
¯
G
¯
, GPO2, and OVP Pins –0.3 to 42 V
EN, VIN, INS, and GATE Pins INS and GATE pins should not exceed VIN by more than 0.4 V –0.3 to 40 V
SW Pin VSW
Continuous –0.6 to 42 V
t < 50 ns –1.0 to 46 V
VDD, FSET/SYNC, COMP, GPO1,
SDA, SCL, and ADDR Pins –0.3 to 5.5 V
Operating Ambient Temperature TAK temperature range –40 to 125 °C
Maximum Junction Temperature TJ(max) 150 °C
Storage Temperature Tstg –65 to 150 °C
[1] Operation at levels beyond the ratings listed in this table may cause permanent damage to the device. The Absolute Maximum ratings are stress ratings only, and func-
tional operation of the device at these or any other conditions beyond those indicated in the Electrical Characteristics table is not implied. Exposure to Absolute Maximum-
rated conditions for extended periods may affect device reliability.
THERMAL CHARACTERISTICS: May require derating at maximum conditions; see application information
Characteristic Symbol Test Conditions [2] Value Unit
Package Thermal Resistance RθJA On 4-layer PCB based on JEDEC standard 28 °C/W
[2] Additional thermal information available on the Allegro website.
SPECIFICATIONS
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
4
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Functional Block Diagram
100 kΩ
Fault
Current
Sense
Diode Open
Sense
OVP Sense
TSD
Open /Short
LED Detect
Enable
Regulator
UVLO
GATE
VDD
VIN
SW
AGND
FSET /SYNC
Bandgap
Reference
Driver
Circuit
Startup/
Shutdown
Oscillator
Internal
V
CC
Internal
V
CC
VOVP REG
OVP
LED1
LED8
...
V
REF
EN
AGND
Register
SDA
SCL
VOVP
10 µA
REG
ADDR
FLAG
I2C
Interface COMP
V
REG
PWM1 to
PWM8
ISET1 to
ISET8
LED Driver
COMP
Fault
Status
INS OCP
`
`
PGND
GPO1
GPO2
MUX
Selector
COMP
PAD
+
–
+
–
+
–
+
–
+
–
+
–
8
88
8
OCP
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
5
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Package LP, 28-Pin TSSOP Pinout Diagram
Terminal List Table
Name Number Function
ADDR 25 This pin has 4 levels that allow the user to set up to 4 physical IC addresses based on the voltage level. Connect a
resistor to GND to set the voltage level.
AGND 7, 15 Analog ground; connect all noise-sensitive components (especially for COMP) to this quiet ground, and connect to
thermal pad.
COMP 6 Output of error amplifier and compensation node; connect a type-2 feedback network from this pin to AGND for
control loop compensation.
EN 4 Enable for the A8522; IC stays in shutdown mode as long as EN = VEN(L)
, enables the part when connected to VEN(H)
or to VIN
.
¯
F
¯
¯
L
¯
¯
A
¯
¯
G
¯ 9This active-low, open-drain pin is used to indicate that system attention is required, such as during startup or a fault
condition. Connect a resistor with a value from 10 to 100 kΩ between this pin and the target logic level voltage.
FSET/SYNC 5 Frequency/synchronization pin; a resistor, RFSET , from this pin to GND sets the switching frequency, and this pin can
also be used to synchronize to an external switching frequency.
GATE 1 Gate driver for optional external PMOS input disconnect switch, that in the event of a fault (such as output shorted to
GND) is turned off by this pin being pulled high (turning off input supply); if not used, this pin should be left open.
GPO1 22 General purpose open-drain output 1, programmable by internal register.
GPO2 21 General purpose open-drain output 2, programmable by internal register.
INS 2 Input current sense, used together with VIN pin to detect input overcurrent fault; if not used, this pin should be tied to
VIN.
LEDx
10, 11, 12,
13, 14, 16,
17, 18
LED current sink channels 1 through 8. Up to 60 mA per channel. Any unused LEDx pin should be connected to GND
through a 4.7 kΩ resistor.
NC 19, 20 No connect. Terminate each pin to GND through a 4.7 kΩ resistor (do not short to GND directly). See page A-8 for
important notes on initialization of register 0x00.
OVP 27 Connect this pin to output voltage VOUT to provide output Overvoltage Protection (OVP) and Undervoltage Protection
(UVP).
PAD –
Exposed pad of the package providing enhanced thermal dissipation. This pad must be connected to the ground
plane(s) of the PCB with at least 8 vias, directly in the pad, and AGND and PGND pins must be connected to this
ground pad on the PCB.
PGND 26 Power ground for internal NMOS switching device; connect this pin to ground terminal of output ceramic capacitor(s)
and to thermal pad.
SCL 24 I2C clock signal.
SDA 23 I2C data signal.
SW 28 The drain of the internal NMOS switch of the boost converter.
VDD 8 Output of internal LDO; connect a 0.47 µF decoupling capacitor between this pin and AGND.
VIN 3 Input power to the A8522.
GATE
INS
VIN
EN
FSET/SYNC
COMP
AGND
VDD
FLAG
LED1
LED2
LED3
LED4
LED5
SW
OVP
PGND
ADDR
SCL
SDA
GOP1
GPO2
NC
NC
LED8
LED7
LED6
AGND
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
PAD
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
6
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Characteristic Symbol Test Conditions Min. Typ. Max. Unit
INPUT VOLTAGE
Input Voltage Range VIN Measured at the VIN pin 4.5 −36 V
VIN Pin UVLO Start VINUV(ON) VIN rising − − 4.35 V
VIN Pin UVLO Stop VINUV(OFF) VIN falling − − 3.90 V
VIN Pin UVLO Hysteresis VINUV(HYS) −400 −mV
INPUT CURRENT
Input Quiescent Current IQMeasured at the VIN pin, EN = VEN(H) ,
fSW = 2 MHz no load −15 −mA
Input Sleep Supply Current IQSLEEP
Sum of VIN and INS pin currents,
VIN = VINS = 16 V, VEN = 0 V −3.5 10.0 µA
EN (ENABLE) PIN
EN Input Logic Level - Low VEN(L) 4.5 V < VIN < 36 V − − 0.4 V
EN Input Logic Level - High VEN(H) 4.5 V < VIN < 36 V 1.5 − − V
EN Internal Pull-Down Resistance RENPD −100 − kΩ
Error Amplifier
Source Current IEA(SRC) VCOMP = 0.75 V, VLEDx = 0.3 V −–200 −µA
Sink Current IEA(SINK) VCOMP = 0.75 V, VLEDx = 1.5 V −+200 −µA
COMP Pin Internal Pull-Down
Resistance RCOMPPD During startup and shutdown −2000 − Ω
OUTPUT OVERVOLTAGE AND UNDERVOLTAGE PROTECTION
Overvoltage Threshold VOVPMIN OVP register = xxx0 0000 7.5 8 8.5 V
VOVPMAX OVP register = xxx1 1111 38 39 40 V
Overvoltage Step Size VOVPSTEP −1.0 −V
Undervoltage Threshold VUVPMIN OVP register = xxx0 0000 −0.49 −V
VUVPMAX OVP register = xxx1 1111 −2.5 −V
OVP Pin Input Impedance ROVP VOVP = 20 V, EN = VEN(H) −800 − kΩ
OVP Leakage Current IOVPLKG VOVP =16 V, EN = VEN(L) −0.1 1 µA
Secondary Overvoltage Protection VOVP(sec) Measured at SW pin −44 −V
BOOST Switch
Switch On-Resistance RDS(ON) ISW = 0.750 A, VIN = 16 V −220 350 mΩ
Switch Leakage Current ISWLKG
VSW = 16 V, EN = VEN(L)
, TA = TJ = –40°C
to 85°C −0.1 10 µA
VSW = 16 V, EN = VEN(L)
, TA = TJ = 125°C −3−µA
Cycle-by-Cycle Switch Current Limit ISW(LIM) 3.6 4.2 4.8 A
Secondary Switch Current Limit [2] ISWLIM(sec)
Higher than maximum ISW(LIM) at any
condition (A8522 latches when detected) 5.6 7.0 −A
Minimum Switch On-Time tSWONTIME RFSET = 10 kΩ − 85 120 ns
Minimum Switch Off-Time tSWOFFTIME RFSET = 10 kΩ − 55 85 ns
Continued on the next page…
ELECTRICAL CHARACTERISTICS [1]: Valid at VIN = 16 V , TA = 25°C, EN = VEN(H) , indicates specications valid across
the full operating temperature range with TA = TJ = –40°C to 125°C and with typical specications at TA = 25°C; unless other-
wise specied
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
7
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Continued on the next page…
Characteristic Symbol Test Conditions Min. Typ. Max. Unit
SWITCHING FREQUENCY
Boost Stage Switching Frequency fSW
RFSET = 10 kΩ 1.8 2 2.2 MHz
RFSET = 20.1 kΩ − 1−MHz
RFSET = 40.6 kΩ − 500 −kHz
FSET/SYNC Pin Voltage VFSETSYNC RFSET = 10 kΩ − 1.00 −V
SYNCHRONIZATION
Synchronized Boost Stage Switching
Frequency fSW_SYNC 400 −2300 kHz
Synchronization Input Minimum
Off-Time tSYNCPWOFF 150 − − ns
Synchronization Input Minimum
On-Time tSYNCPWON 150 − − ns
Synchronization Input Logic – Low VSYNCON(L) − − 0.4 V
Synchronization Input Logic – High VSYNCON(H) 2− − V
LED CURRENT SINKS
LEDx Accuracy (Average) ErrLEDx Measured at ILEDMAX (maximum LED current) −0.7 3 %
LEDx Matching ΔILEDx
Compared to average ILEDx , measured at
ILEDMAX
−0.8 3 %
LEDx Regulation Voltage VREG ISET register= xx11 1111 −0.85 1.0 V
ILEDx Step Size ISETSTEP Total 64 steps 0.9 1 1.1 mA
Maximum LEDx Current (Average) ILEDMAX ISET register = xx11 1111 62 64 66 mA
Minimum LEDx Current ILEDMIN ISET register = xx00 0000 −1−mA
LEDx Short-Detect Threshold VLED_SD
Short-Detect register = 000 −12 −V
Short-Detect register = 111 −5−V
INTERRUPTS (FLAG, GPO1 AND GPO2 PINS)
Pin Pull-Down Voltage Fault / Interrupt condition asserted, pull-up
current = 0.5 mA − − 0.4 V
Pin Leakage Current Fault / Interrupt condition cleared, pull-up to
3.6 V − − 1 µA
INTERNAL MASTER CLOCK
Master Clock Period TCLK 120 150 180 ns
Master Clock Temperature Deviation [2] DTCLK TCLK change over temperature range –2.5 – 2.5 %
ELECTRICAL CHARACTERISTICS [1] (continued): valid at VIN = 16 V , TA = 25°C, EN = VEN(H) , indicates specications
valid across the full operating temperature range with TA = TJ = –40°C to 125°C and with typical specications at TA = 25°C;
unless otherwise specied
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
8
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Characteristic Symbol Test Conditions Min. Typ. Max. Unit
INPUT DISCONNECT
GATE Pin Sink Current IGSINK
VGATE = VIN , no input overcurrent fault
tripped −115 −µA
GATE Pin Source Current IGSOURCE
VGATE = VIN – 5 V, input overcurrent fault
tripped −–6 −mA
GATE Voltage at Off VGSOFF EN = VEN(L)
, or overcurrent fault occurred −VIN −V
GATE Voltage at On VGSON
Gate-to-source voltage when gate is on,
measured as VIN – VGATE
5−8 V
GATE Pin Leakage Current IGLKG EN = VEN(L)
, VGATE = VIN − − 1 µA
INS Pin Sink Current IINSSINK −20 −µA
INS Trip Point VINSTRIP Measured between VIN and INS 90 105 120 mV
INS Trip Detection Time [2] tINSTRIP Sensed voltage, VIN – VINS = 160 mV −2−µs
Thermal Protection (TSD)
Thermal Shutdown Threshold [2] TSD Temperature rising 155 170 −°C
Thermal Shutdown Hysteresis [2] TSDHYS −20 −°C
Thermal Warning Threshold TSDWARN
Temperature rising, measured as difference
from TSD −20 −°C
I2C INTERFACE
Logic Input (SDA, SCL) – Low VSCL(L) − − 0.8 V
Logic Input (SDA, SCL) – High VSCL(H) 2.3 − − V
Logic Input Hysteresis VI2CIHYS −150 −mV
Logic Input Current II2CI –1 −1 µA
Output Voltage SDA VI2COut(L) SDA = low, pull-up current = 2.5 mA − − 0.4 V
Output Leakage SDA II2CLKG EN = low, pull-up to 5.5 V − − 1 µA
SCL Clock Frequency fCLK − − 400 kHz
ADDR PIN
Voltage Level for Address 100,0000 VADDLEVEL1 ADDR connected to GND 0 −0.5 V
Voltage Level for Address 101,0000 VADDLEVEL2 RADDR = 110 kΩ from ADDR to GND 0.9 −1.3 V
Voltage Level for Address 110,0000 VADDLEVEL3 RADDR = 210 kΩ from ADDR to GND 1.75 −2.45 V
Voltage Level for Address 111,0000 VADDLEVEL4 ADDR connected to VDD pin or open 3.2 −3.6 V
ADDR Pull-Up Current IADDR VADDR = 1 V –8.5 –10 –11.5 µA
INTERNAL REGULATOR
Bias Supply Voltage VDD −3.6 −V
[1] For input and output current specifications, negative current is defined as coming out of the node or pin (sourcing), positive current is defined as going into the node or
pin (sinking).
[2] Ensured by design and characterization, not production tested.
ELECTRICAL CHARACTERISTICS [1] (continued): valid at VIN = 16 V , TA = 25°C, EN = VEN(H) , indicates specications
valid across the full operating temperature range with TA = TJ = –40°C to 125°C and with typical specications at TA = 25°C;
unless otherwise specied
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
9
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
CHARACTERISTIC PERFORMANCE
50
60
70
80
90
100
8 10 12 14 16 18 20
Efficiency, η (%)
VIN (V)
Efficiency versus Input Voltage
7 series LEDs, 8 parallel strings at 60 mA each
70
75
80
85
90
95
0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60
Total LED Current (A)
Efficiency versus Output Current
65
70
75
80
85
90
95
12 14 16 18 20 22 24 26 28 30
Efficiency versus Output Voltage
Efficiency, η (%)
Efficiency, η (%)
Efficiency, η (%)
f
SW
= 400 kHz
f
SW
= 2 MHz
7 series LEDs, 8 parallel strings at 60 mA each
f
SW
= 400 kHz
f
SW
= 2 MHz
V
IN
= 12 V
8 parallel strings at 60 mA each 9 series LEDs, 8 parallel strings at 50 mA each, L1
= 47
µH
f
SW
= 400 kHz
f
SW
= 2 MHz
V
IN
= 12 V
4 series
LEDS
5 series
LEDS 6 series
LEDS
7 series
LEDS 8 series
LEDS 9 series
LEDS
9 series
LEDS
8 series
LEDS
7 series
LEDS
6 series
LEDS
5 series
LEDS
4 series
LEDS
70
75
80
85
90
95
0 200 400 600 800 1000 1200 1400 1600 1800 2000 2200
Efficiency versus Switching Frequency
Output Voltage (V)
Switching Frequency (kHz))
V
IN
= 12 V
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
10
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 12 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 100%
Polyphase mode = on
Test conditions:
LED strings = 8 parallel, 30 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 12 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 100%
Polyphase mode = on
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 5.5 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 0.02% at
200 Hz (5000:1)
Polyphase mode = on
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 5.5 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 0.02% at
200 Hz (5000:1)
Polyphase mode = on
Startup Waveform at VIN = 12 V
Dimming PWM Duty Cycle = 100%
Startup Waveform at VIN = 5.5 V
Dimming PWM Duty Cycle = 100%
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C2 (Red) = VSW (20 V/div)
C4 (Green) = ILED (200 mA/div)
Time scale = 20 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C2 (Red) = VSW (20 V/div)
C4 (Green) = ILED (200 mA/div)
Time scale = 20 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C2 (Red) = VSW (20 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 20 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C2 (Red) = VSW (20 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 20 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Thermal derating chart for LED=
Startup Waveform at VIN = 12 V
Dimming PWM Duty Cycle = 0.02%
Startup Waveform at VIN = 5.5 V
Dimming PWM Duty Cycle = 0.02%
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
11
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
PWM Operation with Polyphase
Transient Response to Step-Change
In PWM Duty Cycle ( 2% to 0.02%)
PWM Operation without Polyphase
Transient Response to Step-Change
In PWM Duty Cycle ( 0.02% to 2%)
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
VIN = 12 V
Dimming PWM duty cycle = 2% at 200 Hz
Polyphasemode=o(allsimultaneously
on)
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C4 (Green) = ILED (200 mA/div)
Time scale = 1 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Period
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
VIN = 12 V
Dimming PWM duty cycle = change from
2% to 0.02% at 200 Hz (PWM on-time
change from 100 µs to 1 µs)
Polyphase mode = on
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = I2C clock (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
PWM at 2% PWM at 0.02%
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
VIN = 12 V
Dimming PWM duty cycle = change from
0.02% to 2% at 200 Hz (PWM on-time
change from 1 µs to 100 µs)
Polyphase mode = on
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = I2C clock (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Thermal derating chart for LED=
PWM at 0.02% PWM at 2%
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 12 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 2% at 200 Hz
Polyphase mode = on (each on at assigned
time slot)
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C4 (Green) = ILED (200 mA/div)
Time scale = 1 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Period
Period
/
10
Phase 1
Phase 2
Phase 3
Phase 4
Phase 5
Phase 6
Phase 7
Phase 8
Phase 1
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
12
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
VIN = change from 16 V to 8 V
Dimming PWM duty cycle = 0.02% at
200 Hz
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
VIN = change from 8 V to 16 V
Dimming PWM duty cycle = 0.02% at
200 Hz
Transient Response to Step-Change
In VIN (16 V to 8 V ) PWM Duty Cycle 0.02%
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = VIN (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = VIN (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Transient Response to Step-Change
In VIN (8 V to 16 V ) PWM Duty Cycle 0.02%
Test conditions:
LED strings = 8 parallel, 45 mA each
LEDs = 7 series each string
VIN = change from 16 V to 8 V
Dimming PWM duty cycle = 100%
Test conditions:
LED strings = 8 parallel, 45 mA each
LEDs = 7 series each string
VIN = change from 8 V to 16 V
Dimming PWM duty cycle = 100%
Transient Response to Step-Change
In VIN (16 V to 8 V ) PWM Duty Cycle 100%
Transient Response to Step-Change
In VIN (8 V to 16 V ) PWM Duty Cycle 100%
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = VIN (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Scope traces:
C1 (Yellow) = VOUT (5 V/div)
C3 (Blue) = VIN (5 V/div)
C4 (Green) = ILED (20 mA/div)
Time scale = 10 ms/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
13
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
LED strings = 8 parallel
LEDs = 7 series each string
fSW = 2 MHz
Dimming PWM duty cycle = 100%
Polyphase mode = on
Test conditions:
LED strings = 8 parallel
LEDs = 8 series each string
fSW = 2 MHz
Dimming PWM duty cycle = 100%
Polyphase mode = on
Temperature Rise versus VIN
7 series LEDs in 8 parallel strings
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Temperature Rise versus VIN
8 series LEDs in 8 parallel strings
60 mA
each string
40 mA
each string
30 mA
each string
IC Case Temperature (°C)
V
IN
(V)
IC Case Temperature (°C)
VIN (V)
60 mA
each string
40 mA
each string
30 mA
each string
Switch Node, AC Output Voltage Ripple,
And Inductor Current
Scope traces:
C1 (Yellow) = VOUT (500 mV, AC/div)
C2 (Red) = VSW (10 V/div)
C4 (Green) = IL (inductor current)(200 mA/
div)
Time scale = 200 ns/div
A8522 evaluation PCB:
L1 = 10 µH, COUT5 = 68 µF / 50 V polymer
electrolytic, COUT4 = 2.2 µF /
50 V 1206 ceramic, RZ=10kΩ,CZ = 5.6
nF, CP = 120 pF
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
LED VREG = 0.85 V
VIN = 12 V
VOUT hysteresis = 0.45 V
Dimming PWM duty cycle = 20%
Polyphase mode = on
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
14
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
Q1 = AO4421
CGS = 10 nF
VIN = 12 V
RSENSE = 18 mΩ
GATE is being slowly pulled down (from VIN to VIN – 6.8 V) to control the inrush current.
Test conditions:
Q1 = AO4421
CGS = 10 nF
VIN = 12 V
RSENSE = 18 mΩ
Startup into a VOUT-to-GND short. GATE is pulled high as soon as the input current > 5.8 A, in
order to turn off the input disconnect switch.
Test conditions:
Q1 = AO4421
CGS = 10 nF
VIN = 12 V
RSENSE = 18 mΩ
Output shorted to GND during normal operation, causing a huge inrush current. GATE is pulled
high, in order to turn off the input disconnect switch and prevent damage to the power supply.
Input Overcurrent Protection
Scope traces:
C1 (Yellow) = VIN (2 V/div)
C2 (Red) = VGATE (2 V/div)
C3 (Blue) = VOUT (5 V/div)
C4 (Green) = IIN (1 A/div)
Time scale = 200 µs/div
Scope traces:
C1 (Yellow) = VIN (2 V/div)
C2 (Red) = VGATE (2 V/div)
C3 (Blue) = VOUT (5 V/div)
C4 (Green) = IIN (1 A/div)
Time scale = 50 µs/div
Scope traces:
C1 (Yellow) = VIN (2 V/div)
C2 (Red) = VGATE (2 V/div)
C3 (Blue) = VOUT (5 V/div)
C4 (Green) = IIN (5 A/div)
Time scale = 10 µs/div
Case 1: Normal startup when using input disconnect
switch
Case 2: Output-to-GND short fault occurred before
startup
Case 3: Output-to-GND short occurred during normal
operation
FAULT HANDLING
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
15
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
fSW = 1 MHz
VIN = 6.5 V
VIN intentionally lowered to the point where SW cycle-by-cycle current limit is tripped.
SW operating at maximum on-time initially. Inductor current ramps up and trips
cycle-by-cycle current limit (≈ 4.2 A). Present on-time is truncated immediately. Next
switching cycle starts normally.
Test conditions:
LED strings = 8 parallel, 60 mA each
LEDs = 7 series each string
fSW = 2 MHz
VIN = 12 V
One LED string is disconnected during normal operation. After output trips OVP, the offending
LED string is removed from regulation, while other strings continue to function correctly.
Switch Overcurrent Protection
LED String Open Fault Detection
Scope traces:
C2 (Red) = VSW (10 V/div)
C4 (Green) = IL (1 A/div)
Time scale = 500 ns/div
Scope traces:
C1 (Yellow) = VFLAG (5 V/div)
C2 (Red) = VSW (10 V/div)
C3 (Blue) = VOUT (5 V/div)
C4 (Green) = ILED (100 mA/div)
Time scale = 200 µs/div
Switching
Period
Switching
Period
ton(max)
toff(min)
ton(truncated)
Cycle-by-cycle current limit, ISW(LIM)
One LED string disconnects; VOUT starts to ramp up
OVP trips; IC stops switching
and pulls FLAG low
FLAG cleared as
VOUT drops lower
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
16
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
Test conditions:
BOOST diode becomes open during normal operation. Energy stored in inductor causes a high
voltage across SW. SW DMOS conducts at VSW > 75 V to discharge the energy safely. IC shuts
off after detecting an overvoltage condition at the SW pin.
Test conditions:
BOOST diode is missing during startup. Energy stored in inductor gradually builds up, causing
higher and higher voltage across the SW pin. Eventually the IC shuts off after detecting an
overvoltage fault at the SW pin (VSW > 50 V).
Protection Against Open/Missing BOOST Diode
Scope traces:
C2 (Red) = VSW (20 V/div)
C3 (Blue) = VFLAG (2 V/div)
Time scale = 500 ns/div
Scope traces:
C2 (Red) = VSW (20 V/div)
C3 (Blue) = VFLAG (2 V/div)
Time scale = 200 ns/div
Case 1: BOOST diode becomes open during normal
operation
Case 2: BOOST diode missing during startup
SW secondary OVP tripped at ≈ 46 V
Switching
Period
Wide Input Voltage, Fault Tolerant, Independently Controlled
Multi-Channel LED Driver with I2C Interface
A8522
17
Allegro MicroSystems, LLC
955 Perimeter Road
Manchester, NH 03103-3353 U.S.A.
www.allegromicro.com
The A8522 is an I2C programmable, multi-channel LED driver
for automotive lighting applications. It incorporates a current-
mode boost controller with internal DMOS boost switch, and
8 integrated current sinks to regulate currents through up to
8 LED strings. Each LED string can be independently enabled or
disabled, with its own LED current and PWM duty cycle pro-
grammed through I2C registers.
Enabling the IC
The IC turns on when a logic high signal, VEN(H) , is applied
on the EN pin, and the input voltage present on the VIN pin is
greater than the UVLO threshold, VINUV(ON) . The EN pin is
rated for 40 V, so it can be tied directly to VIN for certain appli-
cations (see Application Information section). In addition, if the
FSET/SYNC pin is pulled low, the IC does not power up.
The A8522 performs a detailed startup sequence, flow chart and
timing diagram are shown in figures 4a to 4c. Before the LEDs
are enabled, the device goes through a system check to determine
if there are any possible fault conditions that might prevent the
system from functioning correctly. Once the LEDs pass the “LED
short during start up” test the FLAG pin will be pulled low for a
short period of time. If no subsequent faults are detected during
this startup sequence, the IC pulls down the GPO2 pin to signal
to the system controller that the A8522 is ready to receive I2C
commands.
The system controller programs the A8522 internal registers
through I2C Write commands, in order to configure individual
LED strings before they can be turned on. On initial startup I2C
should first send a clear command to bit 2 of register bank num-
ber 56, this ensures that an erroneous fault does not prevent the
LEDs turning on. This command is only required on power up
and/or enable (via EN pin) of the A8522. I2C can now communi-
cate regularly with the A8522. Ensure I2C only enables populated
LED’s. If I2C tries to enable unpopulated LED strings an illegal
action is declared and no LEDs will turn on.
In the event of a genuine fault during start up, the FLAG pin is
pulled low, and the system controller can issue I2C Read com-
mands to investigate the status of fault registers. In this instance
I2C should not clear bit 2 of register bank number 56.
The device enters into shutdown mode when the EN pin is pulled
low, VEN(L) .
Frequency Selection and Synchronization
The internally-generated switching frequency of the boost
converter, fSW , is set by the resistor RFSET , connected from the
FSET/SYNC pin to GND. The frequency can be set in the range
from 400 kHz to 2.3 MHz. The switching frequency is deter-
mined according to the following equation:
fSW (MHz) = 19.9 / RFSET (kΩ) + 0.01 (1)
Figure 1 illustrates how fSW varies with RFSET.
Alternatively, the switching frequency can also be synchronized
using an external clock signal on the FSET/SYNC pin. The exter-
nal clock should be a logic signal between 400 kHz and 2.3 MHz.
When an external clock is applied, the RFSET resistor is ignored.
If the A8522 is started up with a valid external SYNC signal, but
the SYNC signal is lost during normal operation, then one of the
following happens:
1. If the external SYNC signal becomes high impedance (open),
theA8522waitsforapproximately6μsfromthelastedge
detected, before it resumes normal operation at the switching
frequencysetbyRFSET.Nofaultagisgenerated.
2. If the external SYNC signal gets stuck low (shorted to
ground), the A8522 will still attempt to operate at switching
frequency set by RFSET. However, since RFSET is shorted
to GND by the external SYNC signal, it will trip the FSET to
GND short fault and shut down the output. The Fault Flag is
pulled low in this case.
FUNCTIONAL DESCRIPTION
Figure 1: Switching Frequency versus Value of the
RFSET Resistor
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
5 10 15 20 25 30 35 40 45 50
Switching Frequency, fSW (MHz)
RFSET (kΩ)