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A6274 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer A6274
Beschreibung Linear Current Regulator and Controller
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 24 Seiten
A6274 Datasheet, Funktion
A6274, A6274-1
A6284, A6284-1
Linear Current Regulator and Controller
for Automotive LED Arrays
FEATURES AND BENEFITS
• 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)
PACKAGES:
20-Pin eTSSOP (LP) with Exposed Thermal Pad
AEC-Q100 qualified
DESCRIPTION
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.
Continued on next page...
APPLICATIONS
• Automotive rear combination light
• DRL/position
• General automotive lighting
Not to scale
Q1
C2
DIM
FULL
D1
D2
D3 C1
R1
C5
EN1
EN2
R2
R3 R4
FFn
R6
R5
R7
R8
R9
C3
GATE COMP OUT
VIN LED1
LED2
EN1 LED3
EN2 LED4
BIAS A6274-84 LED5
VTH
LED6
FFn GND
DR
PWMIN
ISET1
ISET2
C4
A6274-84-DS, Rev. 1
Figure 1: Typical Application Diagram for “-1” Latching Version






A6274 Datasheet, Funktion
A6274, A6274-1
A6284, A6284-1
Linear Current Regulator and Controller
for Automotive LED Arrays
ELECTRICAL CHARACTERISTICS (continued): Valid at VIN = 14 V, VENx = 3.3 V; ● indicates specifications across the full operating tempera-
ture range with TJ = –40°C to 150°C; other specifications are at TJ = 25°C, unless noted otherwise. Refer to Figure 1 for typical application circuit.
Characteristics
Symbol
Test Conditions
Min. Typ.
Max.
Unit
PROTECTION
VIN Required to Derate ILED by 10%
VIN Derating Range (VINth(L) to VINth(H))
MOSFET Drain Short Protection Threshold
MOSFET Drain Short Protection Blank Delay
VINth(L)
VINthd
VOUT(SC)
td(OUT,scblnk)
String Short Detect Voltage
VSC(STRING)
LEDx Not-In-Use Voltage
VLEDx(NULL)
LEDx Pin Source Current
ILEDsrc
LED Connected Detect Time
tLEDdet
LEDx Short-to-Ground Detect Voltage
VLED(SC)
Open-LED Disable Voltage
VOLED_dis
Input Overvoltage Threshold
VVINOV
Thermal Monitor Activation Temperature 2
TJM
Thermal Monitor Low-Current Temperature 2
TJL
Overtemperature Shutdown 2
TJF
Overtemperature Hysteresis 2
TJ(HYS)
PWM DIMMING: INTERNAL AND EXTERNAL
VVTH = 1.84 V
ILED drops from 90% to 50% level
Measure across OUT and GND pins
Protection disabled from enable instance
While LED sinks are in regulation; sensed
from VLEDx to VLEDreg, 5 V < VIN < 18 V
Detect during tLEDdet time period
Source current for Not-In-Use Detection
ENx = high and VGATE ≤ (VIN – 3.3) at startup
Measured at OUT pin, VVTH = 2 V
VEN1 = VEN2 = high
TJ where ILED drops to 90% level
TJ where ILED drops to 35% level
Temperature increasing
Recovery = TJF – TJ(HYS)
19 20
6.4
1
1
1.8
0.18
65
0.26
5
10
43
TJF – 21
TJF – 7
175
30
21
2.6
0.34
95
0.16
V
V
V
ms
V
V
μA
ms
V
V
V
°C
°C
°C
°C
Internal-to-External PWM Mode Delay
External-to-Internal PWM Mode Delay
PWM DIMMING INTERNAL
td(PWM,INEX)
td(PWM,EXIN)
VPWMIN < VLOGIC(L)
1 − µs
− 20 − ms
Maximum PWM-Dimming Frequency
Minimum PWM-Dimming Frequency
fPWM(MAX)
fPWM(MIN)
DPWM5 2
7.15 kΩ between PWMIN and GND
71.5 kΩ between PWMIN and GND
DR driven by resistor divider from BIAS,
VBIAS ÷ VDR = 27.78, PWM = 205 Hz to
2 kHz
195
● 4.5
2050
215
5.0
235
5.5
Hz
Hz
%
PWM Duty Cycle
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
− − 1 μA
Continued on the next page…
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6

6 Page









A6274 pdf, datenblatt
A6274, A6274-1
A6284, A6284-1
Linear Current Regulator and Controller
for Automotive LED Arrays
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).
9.6 V
100
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.
100 TSD
90
Rising
35
25
0
130
145 154
TJ (ºC) TJM
168 171 175
TJL TJF
80
60
40
6.4 V
20
0
10 15 20 25 30 35
VIN (V)
Figure 6: Input Voltage Derating
(VVTH = 1.64 V)
45
40
35
30
25
20
15
10
5
0
1.6 2 2.4 2.8 3.2 3.6
VVTH (V)
Figure 7: Relationship between VINth(L) and
Voltage on the VTH Pin
40
4
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.
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.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
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