A6211
Constant-Current 3-Ampere PWM Dimmable
Buck Regulator LED Driver
Features and Benefits
• Supply voltage 6 to 48 V
• True average output current control
• 3.0 A maximum output over operating temperature range
• Cycle-by-cycle current limit
• Integrated MOSFET switch
• Dimming via direct logic input or power supply voltage
• Internal control loop compensation
• Undervoltage lockout (UVLO) and thermal shutdown
protection
• Low power shutdown (1
μA
typical)
• Robust protection against:
▫
Adjacent pin-to-pin short
▫
Pin-to-GND short
▫
Component open/short faults
Description
The A6211 is a single IC switching regulator that provides
constant-current output to drive high-power LEDs. It integrates
a high-side N-channel DMOS switch for DC-to-DC step- down
(buck) conversion. A true average current is output using a
cycle-by-cycle, controlled on-time method.
Output current is user-selectable by an external current sense
resistor. Output voltage is automatically adjusted to drive
various numbers of LEDs in a single string. This ensures the
optimal system efficiency.
LED dimming is accomplished by a direct logic input pulse
width modulation (PWM) signal at the enable pin.
The device is provided in a compact 8-pin narrow SOIC package
(suffix LJ) with exposed pad for enhanced thermal dissipation.
It is lead (Pb) free, with 100% matte tin leadframe plating.
Package 8-pin SOICN with exposed
thermal pad (suffix LJ):
Applications:
• General Illumination
• Scanners and multi-function printers (light bars)
• Architectural lighting
• Industrial Lighting
• Display case lighting / MR16
Not to scale
Typical Application Circuit
V
IN
(6 to 48 V)
GND
C1
1
R1 2
EN
A6211
7
TON
BOOT
3
6
GND
EN
4
VCC 5
CS
VIN
SW
8
C4
D1
...
L1
LED+
Enable/PWM Dimming
(100 Hz to 2 kHz)
C5
LED–
RSENSE
A6211-DS
A6211
Constant-Current 3-Ampere PWM Dimmable
Buck Regulator LED Driver
Selection Guide
Part Number
A6211GLJTR-T
Operating Ambient
Temperature, T
A
–40ºC to 105ºC
Package
8-pin SOICN with exposed thermal pad
Packing
3000 pieces per 13-in reel
Absolute Maximum Ratings
Characteristic
Supply Voltage
Bootstrap Drive Voltage
Switching Voltage
Linear Regulator Terminal
Enable and TON Voltage
Current Sense Voltage
Operating Ambient Temperature
Maximum Junction Temperature
Storage Temperature
Symbol
V
IN
V
BOOT
V
SW
V
CC
V
EN
, V
TON
V
CS
T
A
T
J
(max)
T
stg
G temperature range
VCC to GND
Notes
Rating
–0.3 to 50
–0.3 to V
IN
+ 8
–1.5 to V
IN
+ 0.3
–0.3 to 14
–0.3 to V
IN
+ 0.3
–0.3 to 7
–40 to 105
150
–65 to 125
Unit
V
V
V
V
V
V
ºC
ºC
ºC
Thermal Characteristics
may require derating at maximum conditions, see application information
Characteristic
Package Thermal Resistance,
Junction to Ambient
Package Thermal Resistance,
Junction to Pad
Symbol
R
θJA
R
θJP
Test Conditions*
4-layer PCB based on JEDEC standard
Value
35
2
Unit
ºC/W
ºC/W
*Additional thermal information available on the Allegro website.
Terminal List Table
Pin-out Diagram
VIN 1
8
SW
Number
1
2
3
Name
VIN
TON
EN
CS
VCC
GND
BOOT
SW
PAD
Function
Supply voltage input terminals
Regulator on-time setting resistor terminal
Logic input for Enable and PWM dimming
Drive output current sense feedback
Internal linear regulator output
Ground terminal
DMOS gate driver bootstrap terminal
Switched output terminals
Exposed pad for enhanced thermal dissipation;
connect to GND
TON 2
PAD
EN 3
7
BOOT
4
5
6
6
GND
CS 4
5
VCC
7
8
–
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A6211
Constant-Current 3-Ampere PWM Dimmable
Buck Regulator LED Driver
Functional Block Diagram
CVCC
CBOOT
D1
L1
LED String
VCC
BOOT
SW
V
IN
VIN
V
REG
5.3 V
V
CC
UVLO
Average
On-Time
Current
Generator
Off-Time
Timer
TON
R
ON
On-Time
Timer
Gate Drive
UVLO
Shutdown
Level Shift
EN
C
COMP
V
CC
UVLO
Thermal
Shutdown
CS
PAD
RSENSE
GND
0.2 V
–
Current Limit
Off-Time
Timer
+
I
LIM
–
+
–
V
IL
= 0.4 V
V
IH
= 1.8 V
+
IC and Driver
Control Logic
Buck Switch
Current Sense
–
+
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
A6211
Constant-Current 3-Ampere PWM Dimmable
Buck Regulator LED Driver
ELECTRICAL CHARACTERISTICS
Valid at V
IN
= 24 V, for T
A
= –40°C to 105°C, typical values at T
A
= 25°C; unless
otherwise noted
Characteristics
Input Supply Voltage
V
IN
Undervoltage Lockout Threshold
V
IN
Undervoltage Lockout Hysteresis
VIN Pin Supply Current
VIN Pin Shutdown Current
BOOT Switch Current Limit Threshold
Buck Switch On-Resistance
BOOT Undervoltage Lockout Threshold
Switching Minimum Off-Time
Switching Minimum On-TIme
Selected On-Time
Load Current Sense Regulation
Threshold
Load Current Sense Bias Current
Internal Linear Regulator
VCC Regulated Output
VCC Current Limit*
Enable Input
Logic High Voltage
Logic Low Voltage
EN Pin Pull-down Resistance
Maximum PWM Dimming Off-Time
Thermal Shutdown
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
T
SD
T
SDHYS
–
–
165
25
–
–
°C
°C
V
IH
V
IL
R
ENPD
t
PWML
V
EN
increasing
V
EN
decreasing
V
EN
= 5 V
Measured while EN = low, during dimming
control, and internal references are powered-on
(exceeding t
PWML
results in shutdown)
1.8
–
–
10
–
–
100
17
–
0.4
–
–
V
V
kΩ
ms
V
CC
I
CCLIM
0 mA < I
CC
< 5 mA, V
IN
> 6 V
V
IN
= 24 V, V
CC
= 0 V
5.0
5
5.3
20
5.6
–
V
mA
Symbol
V
IN
V
UVLO
I
IN
I
INSD
I
SWLIM
R
DS(on)
Test Conditions
T
A
= 25°C
V
IN
increasing
V
CS
= 0.5 V, EN = high
EN shorted to GND
V
BOOT
= V
IN
+ 4.3 V, T
A
= 25°C, I
SW
= 1 A
V
BOOT
to V
SW
increasing
V
CS
= 0 V
V
IN
= 24 V, V
OUT
= 12 V, R
ON
= 137 kΩ
Min.
6
–
–
–
–
3.0
–
1.7
–
–
–
800
Typ.
–
5.3
150
5
1
4.0
0.25
2.9
370
110
110
1000
Max.
48
–
–
–
10
5.0
0.4
4.3
–
150
150
1200
Unit
V
V
mV
mA
μA
A
Ω
V
mV
ns
ns
ns
V
UVLO_HYS
V
IN
decreasing
V
BOOTUV
t
OFFmin
t
ONmin
t
ON
BOOT Undervoltage Lockout Hysteresis V
BOTUVHYS
V
BOOT
to V
SW
decreasing
Regulation Comparator and Error Amplifier
V
CSREG
I
CSBIAS
V
CS
decreasing, SW turns on
V
CS
= 0.2 V, EN = low
187.5
–
200
0.9
210
–
mV
μA
*The internal linear regulator is not designed to drive an external load
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
A6211
Constant-Current 3-Ampere PWM Dimmable
Buck Regulator LED Driver
Characteristic Performance
V
IN
V
IN
V
OUT
C1,C2
C1,C2
V
OUT
i
LED
C3
C3
i
LED
V
EN
C4
V
EN
C4
t
t
Panel 1A. V
IN
= 19 V
Panel 1B. V
IN
= 24 V
V
IN
V
OUT
C1,C2
i
LED
C3
V
EN
C4
t
Panel 1C. V
IN
= 30 V
Figure 1. Startup waveforms from off-state at various input voltages; note that the rise time of the LED current depends on
input/output voltages, inductor value, and switching frequency
• Operating conditions: LED voltage = 15 V, LED current = 1.3 A, R
1
= 63.4 kΩ (frequency = 1 MHz in steady state),
V
IN
= 19 V (panel 1A), 24 V (panel 1B) and 30 V (panel 1C)
• Oscilloscope settings: CH1 (Red) = V
IN
(10 V/div), CH2 (Blue) = V
OUT
(10 V/div),
CH3 (Green) = i
LED
(500 mA/div), CH4 (Yellow) = Enable (5 V/div), time scale = 50
μs/div
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
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