The A6274 and A6284 are programmable linear current
regulator ICs for driving automotive LED arrays. The LED
current is programmed by external resistors. These devices
sink up to 60 mA (A6274) or 120 mA (A6284), from each of
six LED pins, to drive strings of high-brightness LEDs. LED
pins can be paralleled to drive even higher current LED strings.
Current settings are typically accurate to 2%, while typical
matching between LED strings is 0.8%.
LED light output can be adjusted by PWM dimming. The ICs
provide an internal PWM dimming circuit that is programmed
by external resistors for PWM frequency and duty cycle. It
can also accept an external PWM signal. Multiple ICs can be
configured in parallel for larger lighting systems. An internal
FULL (VDR > 3.6 V) option is provided to override the PWM-
dimming ratio for full LED current.
LED current derating with temperature and programmable
VIN levels allows operation over a wide range of operating
conditions.
A6274-84-DS, Rev. 2
• Six LED current sinks rated up to 60 mA (A6274) or
120 mA (A6284)
• Total LED drive current—up to 360 mA or 720 mA
• Wide input voltage range of 5 to 42 V for start/stop, cold-
crank, and load-dump requirements
• Low-dropout voltage—drives two series WLEDs from
7 V input
• Gate driver for external ballast P-MOSFET
• LEDs combined in two groups with separate ENx and
ISETx
• LED current level set by external reference resistors
• Internal or external PWM dimming
• Controlled output drivers slew during PWM for lower
EMI
• Fault detection features: LED string open, LED pin
short-to-ground, single LED short, VOUT short-to-
ground, VIN overvoltage, and thermal protection
• Input supply and temperature-based derating
• Automotive K-temperature range (–40°C to 150°C)
Linear Current Regulator and Controller
for Automotive LED Arrays
PACKAGES:
Not to scale
A6274, A6274-1
A6284, A6284-1
FEATURES AND BENEFITS DESCRIPTION
20-Pin eTSSOP (LP) with Exposed Thermal Pad
AEC-Q100 qualied
Continued on next page...
APPLICATIONS
• Automotive rear combination light
• DRL/position
• General automotive lighting
Figure 1: Typical Application Diagram for “-1” Latching Version
Q1
C3 C4
C2
D1
D2
D3
R1
C5
R3
R2
R4
R5
R8
R9
GATE
VIN
EN1
EN2
BIAS
VTH
FFn
DR
PWMIN
ISET1
ISET2
GND
LED6
LED5
LED4
LED3
LED2
LED1
OUT
COMP
A6274-84
DIM
FULL
FFn
EN2
EN1
R7
C1
R6
January 3, 2017
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
2
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ABSOLUTE MAXIMUM RATINGS
[2]
Characteristic Symbol Notes Rating Unit
VIN, OUT, DR, EN1, EN2, COMP, FFn
VIN, VOUT,
VCOMP
, VDR,
VEN1, VEN2, VFFn
−0.3 to 45 V
GATE VGATE
Max of (–0.3 or
VIN – 9) to 45 V
LED1 to LED6 VLEDx −0.5 to 45 V
All other pins −0.3 to 6.5 V
Junction Temperature TJ−40 to 150 °C
Transient Junction Temperature TJt
Overtemperature event not exceeding 10 seconds, lifetime
duration not exceeding 10 hours, determined by design
characterization.
175 °C
Storage Temperature Range Tstg −55 to 150 °C
2 Stresses beyond those listed in this table may cause permanent damage to the device. The absolute maximum ratings are stress ratings only, and functional 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
Characteristic Symbol Test Conditions [3] Value Unit
Junction-to-Ambient Thermal Resistance RθJA Estimated, on 4-layer PCB based on JEDEC standard 29 °C/W
3 Additional thermal information available on the Allegro website.
SELECTION GUIDE
Part Number ILED(MAX)
FAULT Response
(see Table 2 for details) Package Packing [1]
A6274KLPTR-T 60 mA per channel Unlatched MODE0
20-pin eTSSOP with thermal pad 4,000 pieces per 13-in. reel
A6284KLPTR-T 120 mA per channel Unlatched MODE0
A6274KLPTR-1-T 60 mA per channel Latched MODE1
A6284KLPTR-1-T 120 mA per channel Latched MODE1
1 Contact Allegro™ for additional packing options.
SPECIFICATIONS
A GATE pin is provided to drive an external P-channel MOSFET,
which serves as an active ballast resistor to reduce the heat dissipation
within the IC package. It also serves as an input disconnect switch
in the event of an LED string short-to-ground fault.
The A6274 and A6284 provide a non-latching option while the
A6274-1 and A6284-1 provide a latching option.
DESCRIPTION (continued)
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
3
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package LP, 20-Pin eTSSOP Pinout Diagram
Terminal List Table
Number Symbol Function
1 ISET1
Sets LEDx sink current for LED1-3. Connect
resistor to GND to set current, up to 60 mA
(A6274) or 120 mA (A6284) per channel.
2 ISET2
Sets LEDx sink current for LED4-6. Connect
resistor to GND to set current, up to 60 mA
(A6274) or 120 mA (A6284) per channel.
Connect ISET2 to BIAS if only one resistor
setting is required for LED1-6.
3 VTH
Sets input voltage threshold for current foldback
and VOUT threshold for open-LED fault (D, E, F,
and G) disable threshold.
4 PWMIN
PWM frequency setting. Internal PWM frequency
set when connected to GND through a resistor
and uses external PWM when a logic signal is
applied to this pin.
5 BIAS
Output of internal bias regulator. Connect a
1 µF decoupling capacitor near to IC pin. BIAS
pin can deliver up to 7 mA to an external load.
6 FFn
Active-low fault flag. This pin can be used as
an input pin while using “-1” latching version. If
pulled low, IC will turn all LEDs off for one-out-
all-out functionality across multiple chips in the
system.
7, 8, 9 LED1-3 Three LED current sinks. Connect the cathode of
each LED string to these pins.
10 GND Ground pin.
11, 12, 13 LED4-6 Three LED current sinks. Connect the cathode of
each LED string to these pins.
14 OUT Connect to drain of series-pass MOSFET.
15 COMP
Connect a 470 nF capacitor across COMP pin
and drain node of external PMOS. If PMOS is
not used, connect this pin to VIN.
16 GATE Gate drive for series-pass MOSFET. If PMOS is
not used, connect this pin to VIN.
17 VIN
Input voltage to IC. Connect to source of series-
pass P-channel MOSFET. Connect a decoupling
capacitor close to this pin.
18 EN1 Active-high-enable input for LED1-3.
19 EN2 Active-high-enable input for LED4-6.
20 DR
Voltage on this pin sets dimming duty cycle
when 0 < VDR < 3.6 V. IC operates with 100%
duty cycle in internal and external PWM mode
when VDR > VDRDC(max)
–PAD Thermal pad. Solder to ground plane for better
thermal performance.
ISET1
ISET2
VTH
PWMIN
BIAS
FFn
LED1
LED2
LED3
GND LED4
LED5
LED6
OUT
COMP
GATE
VIN
EN1
EN2
DR
1
2
3
4
5
6
7
8
9
10 11
12
13
14
15
16
17
18
19
PAD
20
PINOUT DIAGRAM AND TERMINAL LIST TABLE
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
4
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Functional Block Diagram
LDO
VBIAS
EN1 EN1
EN2 EN2
VTH
DR
PWMIN
ISET2
ISET1
FFn
GND
LED6
LED5
LED4
LED3
LED2
LED1
VINGATECOMPOUT
FULL
ON/OFF
EN1
EN2
6
6
OUTShort
V
OUTShort
Fault
Driver
Reference
Current
Internal
PWM
Generator
Feedback
and Control
LED
Open/
Short
Detect
A6274-84
TSD
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
5
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
INPUT SPECIFICATIONS
Operating Input Voltage Range VIN ● 5 – 42 V
Input Quiescent Current
[1] IQVENx = high, FULL mode – – 6mA
Input Sleep Supply Current
[1] IQSLEEP VEN1 = VEN2 = 0 V; VDR = VBIAS ● – – 6μA
INTERNAL BIAS CIRCUIT
BIAS Pin Voltage VBIAS IBIAS = 0 to 7 mA, 5.6 V ≤ VIN ≤ 18 V ● 4.75 5 5.25 V
BIAS Pin Dropout VBIASDROP
Minimum voltage drop across VIN and
BIAS pins. IBIAS < 7 mA, VIN = 5 V –0.3 –V
VBIAS Undervoltage Release Threshold VBIASSTART VIN rising ● – – 4.6 V
VBIAS Undervoltage Lockout Stop Threshold VBIASSTOP VIN falling ● – – 4.2 V
P-CHANNEL MOSFET DRIVER SPECIFICATION
GATE Sink Current
[1] IGATE(SINK)
Due to on-chip current limit, 10 V < VIN < 18 V 4– – mA
Due to on-chip current limit, VIN = 5 V 2– – mA
GATE Maximum Voltage (w.r.t. VIN)VGATE(MAX) VIN – VGATE, VLEDx = 0.3 V 8 10 12 V
GATE Minimum Voltage (w.r.t. VIN)VGATE(MIN) VIN – VGATE, VLEDx = 1 V –130 360 mV
PMOS Detect Threshold VGATE(PMOS)
Voltage measured (VIN – VGATE) at end of
startup to detect PMOS connected –600 – mV
LEDx CURRENT DRIVER SPECIFICATION
LEDx Regulation Voltage
[2a] VLEDreg
A6274; not in derating ● – 0.4 0.7 V
A6284; not in derating ● – 0.55 0.85 V
LEDx Accuracy [3] ErrLEDx
Measured at ILED(MAX), LEDx mismatch < 0.5 V,
5 V < VIN < 18 V, TJ = 0°C to 150°C –23.5 %
LEDx Matching
[4] ΔILEDx
ISET2 connected to BIAS; compared to
average ILEDx, measured at ILED(MAX), LEDx
mismatch < 1 V, 5 V < VIN < 18 V
● – 0.8 3 %
Maximum LEDx Current ILED(MAX)
A6274 ● – 60 – mA
A6284 ● – 120 – mA
Minimum LEDx Current ILED(MIN)
A6274 –6– mA
A6284 –12 – mA
Maximum LED Current, ISETx Pin Short-to-
Ground
[2] ILED(ISETshrt)
A6274 –66 – mA
A6284 – 129 – mA
LED Current Ramp Time tRAMP ILEDx 10% to 90% and 90% to 10% – 8– μs
ISETx to ILEDx Gain gILED
A6274 –248 –A/A
A6284 – 492 – A/A
ISETx Voltage Level VISET 0.015 mA ≤ IISETx ≤ 0.3 mA – 1.2 –V
Continued on the next page…
ELECTRICAL CHARACTERISTICS: Valid at VIN = 14 V, VENx = 3.3 V; ● indicates specications across the full operating temperature
range with TJ = –40°C to 150°C; other specications are at TJ = 25°C, unless noted otherwise. Refer to Figure 1 for typical application circuit.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
6
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
PROTECTION
VIN Required to Derate ILED by 10% VINth(L) VVTH = 1.84 V 19 20 21 V
VIN Derating Range (VINth(L) to VINth(H))VINthd ILED drops from 90% to 50% level – 6.4 –V
MOSFET Drain Short Protection Threshold VOUT(SC) Measure across OUT and GND pins – 1–V
MOSFET Drain Short Protection Blank Delay
During Startup td(OUT,scblnk_strt) Protection disabled from enable instance – 12 – ms
MOSFET Drain Short Protection Blank Delay
During Steady-State td(OUT,scblnk_stdy) Protection blank time – 1– µs
String Short Detect Voltage VSC(STRING)
While LED sinks are in regulation; sensed
from VLEDx to VLEDreg, 5 V < VIN < 18 V 1.8 –2.6 V
LEDx Not-In-Use Voltage VLEDx(NULL) Detect during tLEDdet time period 0.18 0.26 0.34 V
LEDx Pin Source Current ILEDsrc Source current for Not-In-Use Detection 65 – 95 μA
LED Connected Detect Time tLEDdet ENx = high and VGATE ≤ (VIN – 3.3) at startup – 5 – ms
LEDx Short-to-Ground Detect Voltage VLED(SC) − − 0.16 V
Open-LED Disable Voltage VOLED_dis Measured at OUT pin, VVTH = 2 V –10 –V
Input Overvoltage Threshold VVINOV VEN1 = VEN2 = high – 43 –V
Thermal Monitor Activation Temperature
[2] TJM TJ where ILED drops to 90% level – TJF – 21 –°C
Thermal Monitor Low-Current Temperature
[2] TJL TJ where ILED drops to 35% level – TJF – 7 – °C
Overtemperature Shutdown
[2] TJF Temperature increasing − 175 − °C
Overtemperature Hysteresis
[2] TJ(HYS) Recovery = TJF – TJ(HYS) −30 −°C
PWM DIMMING: INTERNAL AND EXTERNAL
Internal-to-External PWM Mode Delay td(PWM,INEX) −1− µs
External-to-Internal PWM Mode Delay td(PWM,EXIN) VPWMIN < VLOGIC(L) −20 − ms
PWM DIMMING INTERNAL
Maximum PWM-Dimming Frequency fPWM(MAX) 7.15 kΩ between PWMIN and GND − 2050 − Hz
Minimum PWM-Dimming Frequency fPWM(MIN) 71.5 kΩ between PWMIN and GND 195 215 235 Hz
PWM Duty Cycle
DPWM5
[2]
DR driven by resistor divider from BIAS,
VBIAS ÷ VDR = 27.78, PWM = 205 Hz to
2 kHz
● 4.5 5.0 5.5 %
DPWM90
DR driven by resistor divider from BIAS,
VBIAS ÷ VDR = 1.54, PWM = 205 Hz to
2 kHz
87 90 93 %
VDRDC(MAX)
Minimum required voltage on DR for 100%
duty cycle 3.6 − − V
DR Pin Current
[1] IDR(SRC) VDR = 2 V − − 1μA
ELECTRICAL CHARACTERISTICS (continued): Valid at VIN = 14 V, VENx = 3.3 V; ● indicates specications across the full operating tempera-
ture range with TJ = –40°C to 150°C; other specications are at TJ = 25°C, unless noted otherwise. Refer to Figure 1 for typical application circuit.
Continued on the next page…
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
7
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Characteristics Symbol Test Conditions Min. Typ. Max. Unit
LOGIC SIGNAL SPECIFICATIONS
FFn Output (Open Drain) VFFn(L) IFFn = 1 mA, fault asserted – – 0.4 V
FFn Output Leakage Current
[1] IFFn(LKG) VFFn = 12 V, fault not asserted –1 – 1 µA
PWMIN, ENx Low Voltage VLOGIC(L) ● – – 0.8 V
PWMIN, ENx High Voltage VLOGIC(H) ●2– – V
FFn Input Low Voltage VFFLOGIC(L)
MODE = 1; FFn pin acts as bidirectional
pin when MODE = 1 ● – – 0.8 V
FFn Input High Voltage VFFLOGIC(H) ●2.1 – – V
PWMIN Input Hysteresis VLOGIC(HYS) 150 270 – mV
ENx Input Hysteresis VLOGIC(HYS1) 40 – – mV
ENx Internal Pull-Down Resistance RPD(ENx) −200 − kΩ
COMP SPECIFICATIONS
COMP Source Current ICOMP(SOURCE) −320 −µA
COMP Sink Current
[2] ICOMP(SINK) − –320 − µA
COMP Startup Sinking Current ICOMP(START) VLEDx is < regulation voltage − 2− mA
1 For input and output current specifications, negative current is defined as coming out of the node or pin (sourcing), and positive current is defined as going into the node
or pin (sinking).
2 Ensured by design and characterization, not production tested.
2a Max limit ensured by design and characterization, not production tested.
3 LED accuracy is defined for A6274 as |[1 – (RISETx × ILED(avg) ÷ 298)]| and for A6284 as |[1 – (RISETx × ILED(avg) ÷ 590)]|,
where ILED(avg) is the average of ILED1 through ILED6, RISETx is in kΩ, and ILED is in mA.
4 LED current matching is defined as [(ILEDx – ILED(avg)) ÷ ILED(avg)], with ILED(avg) as defined in Footnote 3.
ELECTRICAL CHARACTERISTICS (continued): Valid at VIN = 14 V, VENx = 3.3 V; ● indicates specications across the full operating tempera-
ture range with TJ = –40°C to 150°C; other specications are at TJ = 25°C, unless noted otherwise. Refer to Figure 1 for typical application circuit.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
8
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
FUNCTIONAL DESCRIPTION
Powering Up
The A6274/84 can be enabled either by ENx inputs or by input
voltage as shown in Figure 3 and 4 respectively. In both cases, the
IC starts when the internal bias circuit voltage, VBIAS, rises above its
starting level, VBIASSTART
. Any existing latched fault is cleared.
The IC shuts down when input voltage or both ENx inputs fall such
that the internal bias circuit voltage, VBIAS, drops below its stopping
level, VBIASSTOP
.
EN1 is the active-high-enable input for LED1-3 while EN2 is the
active-high-enable input for LED4-6. To drive all the LED strings
with common EN input, connect EN1 and EN2 together. EN1 and
EN2 pins are high-voltage tolerant and can be directly connected to a
power supply.
Refer to Figure 3 for startup with ENx. Once ENx goes high,
the BIAS regulator is allowed to start after a few microsec-
onds internal delay (A to B), and the IC powers up when
VBIAS > VBIASSTART (at C). Once the IC powers up, it will
check LEDx pin voltage to identify if any LEDx pin is used,
unused, or shorted to ground.
After startup, for the time period of tLEDdet (C to D), the IC
detects unused LED sink pins by injecting current ILEDsrc to
LEDx pins and measures voltage on the LEDx pins. If the LEDx
voltage is equal to VLEDx(NULL), the IC detects it as an unused
channel and disables the corresponding LEDx channel. The inter-
nal current source, ILEDsrc, is removed after tLEDdet time period
and disabled strings will be removed from the regulation loop.
The unused pin, with the pull-down resistor, will be taken out of
regulation at this point and will not contribute to the series-pass
regulation loop or fault detection. The FFn pin remains high dur-
ing the tLEDdet period. The enabled strings will be continuously
monitored, and can be treated as a fault after the tLEDdet period.
All unused pins must be connected with a resistor connected from
LEDx to ground, as shown in Figure 2. LEDx pins source ILEDsrd
current. Voltage on an LEDx pin, when connected through resis-
tor, will be VLEDx(NULL).
FULL and DIM Mode
When the DR pin voltage is above VDRDC(MAX), the LEDs
operate with 100% duty cycle (FULL mode). In FULL mode,
the LEDs turn on with 100% duty cycle regardless of internal
or external PWM mode. When the DR pin voltage is lower than
VDRDC(MAX), the LEDs operate with PWM dimming (DIM
mode). PWM frequency and duty cycle in DIM mode is con-
trolled by the PWMIN and DR pins.
Table 1: LED Detection Voltage Thresholds
LED Pin Voltage Level LED Pin Action
VLED(SC) (<160 mV) Indicates short-to-ground FFn goes low after tLEDdet time period.
VLEDx(NULL)
(>180 mV, <340 mV) Not used Unused LEDx is removed from regulation loop. Related sink remains disabled and
latched until it is re-enabled.
VLEDx(NULL,max) (>400 mV) LED pin in use None
GATE
VIN
EN1
EN2
BIAS
VTH
FFn
DR
PWMIN
ISET1
ISET2
GND
LED6
LED5
LED4
LED3
LED2
LED1
OUT
COMP
A6274-84
3.3 kΩ
3.3 kΩ
Figure 2: Channel-select setup using LED1-4; LED5-6 un-
used. LED5-6 connected through 3.3 kΩ resistor to GND.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
9
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 3: Typical Start Sequence with ENx
VIN
EN1 = EN 2
VBIAS
VOUT
FFn
V
BIASSTART
V
LEDx(NORMAL)
I
LEDx(NORMAL)
I
LEDx(DISABLED)
V
LEDx(DISABLED)
I
LEDx(TOTAL)
AB CD
FULL MODE DIM MODEt
LEDdet
EF
V
LEDreg
I
LEDsrc
V
LEDx(NULL)
I
LED(PEAK)
total
I
LEDsrc
I
LED(PEAK)
/ Channel
> V
LEDx(NULL)
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
10
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Figure 4: Typical Start Sequence with VIN
VIN
EN1 = EN 2
VBIAS
VOUT
FFn
VLEDx(NORMAL)
ILEDx(NORMAL)
ILEDx(DISABLED)
V
LEDx(DISABLED)
ILEDx(TOTAL)
VBIASSTART
AB CD
FULL MODE DIM MODEtLEDdet
VLEDreg
ILEDsrc
VLEDx(NULL)
ILED(PEAK) total
ILEDsrc
ILED(PEAK) / Channel
> VLEDx(NULL)
VIN MIN
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
11
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
PWM Dimming in DIM Mode
LED dimming during DIM mode can be controlled internally by
the A6274/84, or externally. For external PWM mode, connect an
external clock pulse on the PWMIN pin, which controls dim-
ming, frequency, and duty cycle. The A6274/84 detects the logic
level on the PWMIN pin. When logic voltage is applied on the
PWMIN pin, the IC switches to external PWM mode where dim-
ming, frequency, and duty cycle are directly controlled by signals
on PWMIN pin.
In internal PWM mode, dimming frequency can be set using a
resistor connected from PWMIN pin to GND as shown in Fig-
ure 1. It is not necessary to select the PWM mode before startup:
the IC will transition from internal to external when PWMIN is
raised above VLOGIC(H); and it will transition from external to
internal when external PWMIN signal is removed for more than
20 ms. LEDx will not blink; they will be off during this period.
The recommended range for PWM frequency is 200 Hz to 2 kHz.
Maximum PWM frequency is limited due to acceptable error
at minimum PWM duty cycle. At higher PWM frequency and
smaller duty cycles, error in LED current increases due to slow
ramp-up and ramp-down in LED current. It is recommended to
use a minimum on-time > 20 µs.
The equation for internal PWM frequency setting with the
PWMIN pin resistor is given by:
fPWM = (14165 ÷ RFPWM) + 19
where fPWM is in Hz and RFPWM is in kΩ. For example, with a
29.4 kΩ resistor, fPWM = 500 Hz.
RFPWM must be greater than 5 kΩ for internal PWM; below this
value, the PWMIN pin is detected at a logic-low level and oper-
ates in external PWM mode.
The voltage on the DR pin determines the operating duty cycle.
For better accuracy, derive this voltage from BIAS using a volt-
age divider. The PWM duty cycle depends on the ratio of the DR
and BIAS pin voltages. The duty cycle can be reduced, down to
5% (see Figure 5), as:
PWM (%) = 139 × VDR ÷ VBIAS
where VDR and VBIAS are in volts (V).
LED Current Setting
The peak LED current can be set at up to 60 or 120 mA per chan-
nel through the ISETx pin. ISET1 sets current through LED1-3
and ISET2 sets current through LED4-6.
By connecting ISET2 to BIAS, ISET1 current can be mirrored on
all enabled LED channels (LED1-6). This will improve current
matching between LED1-6 when all LED strings are identical.
Connect a resistor, RISETx, between ISETx pin and ground, to set
peak LED current through each channel. The value of peak LED
current through each LEDx sink is given by:
ILED(PEAK) = 298 ÷ RISETx (kΩ) for A6274
ILED(PEAK) = 590 ÷ RISETx (kΩ) for A6284
where ILED is in mA and RISETx in kΩ. This sets the peak current
through each LEDx, referred as the 100% Current. The average
LEDx current can be reduced from the 100% Current value by
dimming PWM duty ratio.
0
20
40
60
80
100
00.6 1.2 1.8 2.4 3.0 3.6
VDR (V)
PWM Duty Cycle (%)
Figure 5: Relationship of Voltage on DR pin (VDR)
and Dimming Duty Cycle
VDR can be varied from 0 to 3.6 V
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
12
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Input Overvoltage Derating
This feature takes effect at higher VIN levels, limiting power
dissipation in the IC and the external MOSFET. At higher input
voltages, output current drops corresponding with increasing VIN.
Output current is controlled with peak current (see Figure 6). The
VIN threshold can be set with an external resistor divider con-
nected from BIAS to VTH. The LED current drops to 90% at the
VINth(L) level and to 50% at VINth(H) level. LED current further
drops to 40% and stays at this level for higher input voltages.
Voltage on VTH pin sets the VINth(L) level, and the VINth(H) level
is typically higher than VINth(L) by VINthd (6.4 V).
The recommended range for VINth(L) is from 18 to 36 V.
VINth(L) = 10 × VVTH + 1.6
where VINth(L) is the supply voltage level where LED current
drops to the 90% level, and VVTH is the voltage on VTH pin. Fig-
ure 7 shows relation between voltage on VTH pin and VINth(L).
Thermal Derating and Protection Shutdown
This feature takes effect at higher temperatures, limiting power
dissipation in the IC and external MOSFETs. At higher tempera-
tures, the LED current drops with increasing TJ, as shown in Fig-
ure 8. Thermal shutdown (TSD) completely disables the outputs
under extreme overtemperature (>175°C) conditions, and FFn
goes low. The IC restarts when the temperature drops by 30°C.
Operation of the Series-Pass Regulator
The A6274/84 consists of six regulated and matched current
sinks, and a series-pass regulator controller to minimize power
dissipation in the sinks. The series-pass regulator is controlled
such that all LEDx pin voltage is above regulation. LEDx pin
having maximum forward voltage drop will be regulated by
series-pass regulator. This ensures optimum voltage supplied to
common-anode node of LED strings to drive all strings at the
desired current.
A capacitor connected across COMP to the drain of the external
MOSFET provides a pole for control-loop stability. It is recom-
mended to use NTB5605 or NTD2955 as external PMOS.
When the external PMOS is not used, connect the GATE and
COMP pins to VIN. When the PMOS pre-regulator is not used,
the LED string short faults B and C will be disabled.
0
20
40
80
100
10 15 20 25 40
VIN (V)
LED Current Drop (%)
30 35
60
V
INth(L)
V
INth(H)
6.4 V
9.6 V
Figure 6: Input Voltage Derating
(VVTH = 1.64 V)
15
20
25
30
35
40
1.6 2 2.4 2.8 3.2 3.6
4
VVTH (V)
V
INth(L)
(V)
45
10
5
0
Figure 7: Relationship between VINth(L) and
Voltage on the VTH Pin
0
25
35
90
100 TSD
130 145 154 175
TJ (ºC)
168 171
TJM TJL TJF
Falling
Rising
LED Current Drop (%)
Figure 8: Output Current Foldback Based on Rising TJ
Output current changed by DC current control; when temperature
exceeds 175°C (typ), the IC turns off due to TSD function, and turns
on again at 145°C (30°C (typ)) hysteresis.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
13
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
MOSFET Drain Short to GND Fault (FAULT A)
This fault is detected when the voltage at OUT pin drops below
VOUT(SC). If the OUT-to-ground short circuit is caused by a weak
shorting link, voltage on OUT pin may not drop below VOUT(SC).
In that case, this fault will not be detected and high current will
flow through the MOSFET.
During startup, the MOSFET drain short to GND is detected after
td(OUT,scblnk_strt) delay from part enabled (ENx pin pulled high and
VBIAS > VBIASstart). During this period, the MOSFET may draw
significant current. Current through the MOSFET is limited by
Rds(on) of the MOSFET and external parasitic resistance from bat-
tery to MOSFET source.
During normal operation, the MOSFET drain short to GND fault
is blanked for td(OUT,scblnk_stdy) period.
Open-LED (FAULTs D, E, F, and G)
During normal operation, if the voltage on any enabled LED
pin drops too low (VLEDx < VLED(SC)) and VOUT is greater than
VOLED_dis, it may indicate either a short across LEDx and GND
(Fault E), an open-LED (Fault F), a mid-LED-string short-to-
ground (Fault D), or LED common-anode open (Fault G).
LEDs in faults D and E will only be reported on FF pin, but will
not be protected, if MOSFET Q1 is not used.
Short LED Faults (FAULTs B and C)
Short LED faults are detected while LED sinks are in regulation
and VLEDx – VLEDreg > VSC (STRING).
Open-LED Disable Threshold
At power-up (EN1 or EN2 raised to logic high), if the input volt-
age is below VOLED_dis, faults D, E, F, and G will be disabled.
Once VIN is raised above VOLED_dis, the faults are enabled and
will remain enabled unless VBIAS drops below VBIASSTOP
. The
IC will continue to operate normally in cases where these faults
exist. VOLED_dis value is given by:
VOLED_dis = 5 × VVTH
Voltage on VTH pin sets the input voltage derating threshold
(VINth(L)) as well as the open-LED disable level (VOLED_dis).
Select the VVTH voltage suitable to avoid an open-LED fault due
to insufficient input voltage.
Q1
GATE
VIN
GND
LED6
LED5
LED4
LED3
LED2
LED1
OUT
A6274-84
A
B
C
D
E
H
FG
VIN
COMP
C3 C4
C2
C1 EN1
EN2
BIAS
VTH
FFn
DR
PWMIN
ISET1
ISET2
Figure 10: Various Faults Handled by A6274/84
Gate
Driver
Min
Select
Q1
C3 C4
0.4 V
LED6
LED2
LED1
VIN VOUT
IREF
AR1
SW1
S1
S2
S6
PWM
Generator
DR
PWMIN
Figure 9: External MOSFET Regulator Loop
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
14
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Table 2: Fault Description
Fault Detection Criterion Auto-
Restart FFn LED
Sinks
Ballast
MOSFET
Q1
Operation
MODE State → 1 0 1 or 0 1 0 1 0 1 0
AMOSFET drain
shorted to ground
VOUT < VOUT(SC).
Fault detected after
td(OUT,scblnk_strt) blanking
time from Q1 gate
enabled. During normal
operation, this blanking
time is td(OUT,scblnk_stdy).
No Low All Turn
Off Turn Off IC shutdown and FFn pin goes low. This state remains latched until VIN or any
ENx toggled.
Group 1 Faults Based on Maximum LEDx Pin Voltage
B One LED short
While LED sinks are in
regulation. Sensed from
VLEDx to VLEDreg.
VLEDx – VLEDreg >
VSC(STRING)
No Yes Low
All Turn Off
Operate Normally
Turn Off
Operate Normally
IC shutdown and
FFn pin goes
low. This state
remains latched
until VIN or any
ENx toggled.
LEDx pin voltage on faulty string increases and IC detects
the fault. IC responds only by pulling FFn pin low as long
as fault present. Power dissipation in the faulty LED sink
increases and may hit TSD. Current in LED still regulated
to set level. FFn stays low as long as fault detected.
C Short LED string “.” No Yes Low “.” “.” “.” “.”
IC shutdown and
FFn pin goes
low. This state
remains latched
until VIN or any
ENx toggled. LED
pins rated for
45 V to protect IC
against this fault.
LEDx pin voltage on faulty string increases and IC detects
the fault. IC responds only by pulling FFn pin low as long
as fault present. Power dissipation in the faulty LED sink
increases and may hit TSD. Current in LED still regulated
to set level. FFn stays low as long as fault detected.
LED pins rated for 45 V to protect IC against this fault.
Group 2 Faults Based on LEDx Pin Voltage VLED(SC)
DMid-LED-string
short-to-ground
VOUT > VOLED_dis and
any enabled LEDx pin
voltage < VLED(SC)
No Yes Low
All Turn Off
Operate Normally
Turn Off
Operate Normally
IC shutdown and
FFn pin goes
low. This state
remains latched
until VIN or any
ENx toggled.
LEDx pin voltage on faulty string drops and IC detects the
fault. For a brief time, VOUT increases due to open-loop
operation. Q1 turns on harder as the LEDx pin voltage on
faulty string drops below regulation. VOUT rises close to
VIN. VOUT drops to regulation level after removing the faulty
string from regulation loop. The faulty string removed from
Q1 regulation loop and sinks turned off.
During output overshoot time, Fault B may also be detected
by the IC but it does not affect the operation.
Faulty string will be out of Q1 loop regulation until voltage
on faulty string rises above regulation level or VIN or any
ENx toggled. FFn pin stays low as other string shorted to
ground.
ELEDx pin short-
to-ground “.” No Yes Low “.” “.” “.” “.” “.” “.”
F LED string open “.” No Yes Low “.” “.” “.” “.” “.” “.”
GLED common-
anode open “.” No Yes Low “.” “.” “.” “.” “.”
Voltage on all LED pins drop below regulation level. VOUT
rises close to VIN and stays at this level as all LEDx pins
removed from regulation. Sinks remain active and internal
gate of sink driver rails high. When a string connected back,
VOUT controlled by this string. There will be a small LED
current overshoot. FFn pin stays low if any string is open.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
15
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Table 2: Fault Description (continued)
FAULT Detection Criterion Auto-
Restart
FFn
FAULT
LED
Sinks
Ballast
MOSFET Operation
MODE State → 1 or 0 1 or 0 1 or 0 1 or 0 1 or 0
HString-to-
string short
This condition is not
detected
Operate
Normally Normal Operate
Normally
Operate
Normally
IC operates normally. LED currents in shorted string may not
share same current
Thermal
Shutdown
Junction
temperature
exceeds TJF
Yes Low All Turn
Off Turn Off
IC shutdown and FFn pin goes low. This state remains
latched and re-enables when junction temperature drops
below 145°C. This is a non-latching fault, but this fault leads
to a Fault A condition if thermal shutdown is long enough to
allow the OUT capacitor to fully discharge.
Thermal
Derating
Junction
temperature
exceeds TJM
Operate
Normally Normal
LED
current
derated
based on
TJ
Operate
Normally LED current derated based on junction temperature
VIN Derating
Input voltage VIN
exceeds threshold
set by voltage on
VTH pin
Operate
Normally Normal
LED
current
derated
based on
VIN
Operate
Normally
LED current derated based on supply voltage and VVTH
setting.
Undervoltage
Protection
VBIAS below
VBIASSTART
Yes Low All Turn
Off Turn Off All faults cleared when this fault occurs. IC restarts when
VBIAS > VBIASSTART
VIN
Overvoltage
Input voltage VIN
exceeds VINOVth
level
Yes Low All Turn
Off Turn Off
This is a non-latching fault but this fault leads to a Fault A
condition if the overvoltage is long enough to allow the OUT
capacitor to fully discharge.
Notes:
• If the non-latching fault condition causes OUT voltage to drop below VOUT(SC), the IC will latch as described in Fault A.
• Once faulty condition is detected, FFn goes low after fault blanking time. Fault blanking time for Fault A is 1 µs; fault blanking time for Fault B and C is 3 µs; fault blanking
time for Fault D, E, F, and G is 65 µs.
• For non-latching part, ignore FFn status when duty cycle is below 5%.
• For non-latching part, it is recommended to use a small capacitor of 4.7 nF from FFn to GND with a 10 kΩ FFn pull-up resistor during dimming mode.
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
16
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Power Derating Based on TJ
An external MOSFET dissipates excess voltage (VIN, VLED,
VLEDreg) and minimizes power loss in sinks. When an external
MOSFET is not used, as shown in Figure 17, internal sinks drop
this excess voltage, and power dissipation in sinks increases. The
A6274/84 derates the LED current based on junction temperature
to extend its operating range. A typical example (below) shows
LED current derating and junction temperature of the IC (TJ) at
different VIN conditions.
Table 3: LED Current Derating and Junction Temperature of the IC (TJ) at Different VIN Conditions
Symbol Value Units Description
VLED 7 V Total LED string voltage at desired LED current
IOUT 0.36 A Total LED current
TA90 °C Ambient temperature
RθJA 30 °C/W Junction-to-ambient thermal resistance for the IC
TJM 154 °C Junction temperature at which LED current drops to 90% level. Refer to Figure 8.
VIN(MIN) 9VMinimum input voltage
VIN(MAX) 40 V Maximum input voltage
0.00
0.05
0.15
0.20
0.30
0.40
812 20 24 32 36 40
V
IN
I
OUT
(A)
0.10
0.35
0.25
16 28
Figure 11: Thermal Derating
80
90
110
120
160
180
812 20 28 36 40
VIN
T
J
100
170
150
16 32
24
140
130
0.00
0.05
0.15
0.20
0.30
0.40
140 145 155 160 170 175
TJ
IOUT (A)
0.10
0.35
0.25
150 165
(a) Output combined LED current derating with supply voltage variation.
LED current drop at higher VIN due to excessive power dissipation. (b) Junction temperature TJ of the IC with supply voltage variation
(c) Output combined LED current derating with junction temperature of the IC
EXAMPLE 1
Linear Current Regulator and Controller
for Automotive LED Arrays
A6274, A6274-1
A6284, A6284-1
17
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Power Derating Based on Input Supply Volt-
age VIN
The A6274/84 derates LED current based on the supply voltage
and reference voltage on the VTH pin. Power dissipation in the
external transistor can be limited at higher input voltage. The
example below shows the selection of VVTH to limit MOSFET
junction temperature below 140°C. Refer to Figure 1 for typical
application.
Table 4: LED Current Derating and Junction Temperature of the IC (TJ) at Different VIN Conditions
Symbol Value Units Description
VLED 7 V Total LED string voltage at desired LED current
IOUT 0.36 A Total LED current
TA90 °C Ambient temperature
RθJA 10 °C/W Junction-to-ambient thermal resistance for MOSFET
VLEDreg 0.4 V LEDx pin regulation voltage
VIN(MIN) 9VMinimum input voltage
VIN(MAX) 40 V Maximum input voltage
VVTH 1.64 V External voltage applied to VTH pin
VINth(L) 18 V Input voltage at which LED current drops to 90% level; refer to Figure 7
0
2
6
8
12
0515 20 35 40 45
VIN (V)
Q1 PD (W)
4
14
10
10 30
25
without thermal derating
with thermal derating
Figure 12: Input Voltage Derating
0.00
0.05
0.15
0.20
0.30
10 15 25 35 40
VIN (V)
Worst-Case P
D
in IC (W)
0.10
0.35
0.25
20 30
0
20
60
100
140
10 15 25 35 40
VIN (V)
Q1 T
J
40
160
120
20 30
80
(a) Power Dissipation in MOSFET (RED – unlimited power dissipa-
tion, Blue – Power dissipation with VIN derating) (b) Worst-Case Power Dissipation in IC
(d) MOSFET Junction Temperature
0.00
0.05
0.15
0.25
0.35
10 15 25 35 40
VIN (V)
I
OUT
(A)
0.10
0.40
0.30
20 30
0.20
(c) Output Current Derating
EXAMPLE 2