Description
The A6210 is a buck regulator that uses valley current-mode
control. This control scheme allows very short switch on-times
to be achieved, making it ideal for applications that require
high switching frequencies combined with high input voltages
and low output LED span voltages.
Low system cost is accomplished through high switching
frequencies of up to 2.0 MHz, allowing smaller and lower value
inductors and capacitors. In addition, few external components
are required through high levels of integration. Optimal drive
circuits minimize switching losses.
The switching frequency is maintained constant, as the on-time
is modulated by the input voltage. This feed-forward control
ensures excellent line correction. The on-time is set by an
external resistor pulled-up to the input supply.
Internal housekeeping and bootstrap supplies are provided
which require the addition of only one small ceramic capacitor. A
top-off charge pump ensures correct operation at light loads.
Internal diagnostics provide comprehensive protection against
input undervoltages and overtemperatures.
The device package is a 16-contact, 4 mm × 4 mm, 0.75 mm
nominal overall height QFN, with exposed pad for enhanced
thermal dissipation. It is lead (Pb) free, with 100% matte tin
leadframe plating.
6210-DS, Rev. 2
Features and Benefits
User-configurable on-time, achieving switching
frequencies up to 2.0 MHz
Brightness control through PWM of DIS pin
Minimal external components required
No output capacitor required
Wide input voltage range: 9 to 46 V
Low 0.18 V sense voltage for higher efficiency
Output Current: up to 3.0 A
Low standby current <100 A
Thermal shutdown
Supplied in a thermally-enhanced 4 mm QFN package
3 A, 2 MHz Buck-Regulating LED Driver
Applications:
Typical Application
A6210
GNDNC
L
D1 LED1
LED2
LED3
1
68 H
LX
VIN
ISEN
SGND
A 6210
TON
22 nF
R1
150 k
C1
1.0 F
390 m
DIS
PWM or Switch
R2
C2
BOOT
VIN 24 V
LED span voltage = 10.5 V
Average LED current = 500 mA
Peak to peak current = 60 mA
Switching frequency = 1.4 MHz
Efficiency = 90.5%
Package 16-contact QFN (suffix EU):
High brightness LEDs
LED driver modules, power supplies and lamps, such as
MR16 and MR11
4 mm × 4 mm × 0.75 mm
Suggested Parts
Name Description Manufacturer - Part Number
C1 1 F, 25V, X5R or X7R ceramic, 1210 Taiyo Yuden, TDK
C2 22 nF, 50V, X5R or X7R ceramic, 0805
D1 1 A, 30 V, Schottky diode
L1 68 H, 1 A inductor Taiyo Yuden - NR 6045T 680M
R1 180 k, 1%, 0805
R2 390 m, 1%, 0805
3 A, 2 MHz Buck-Regulating LED Driver
A6210
2
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Absolute Maximum Ratings (reference to GND)
Characteristic Symbol Notes Rating Units
VIN Pin Supply Voltage VIN –0.3 to 50 V
LX Pin Switching Node Voltage VLX –1 to 50 V
ISEN Pin Current Sense Voltage VISEN –1.0 to 0.5 V
DIS Pin Disable Voltage VDIS –0.3 to 7 V
TON Pin On-Time Voltage VTON –0.3 to 50 V
Operating Ambient Temperature TARange G –40 to 105 ºC
Maximum Junction Temperature TJ(max) 150 ºC
Storage Temperature Tstg –55 to 150 ºC
Selection Guide
Part Number Packing Package
A6210GEUTR-T 1500 pieces per reel 16-contact 4 mm × 4 mm QFN with exposed thermal pad
Thermal Characteristics may require derating at maximum conditions, see application information
Characteristic Symbol Test Conditions* Value Units
Package Thermal Resistance,
Junction to Ambient RJA On 4-layer PCB based on JEDEC standard 36 ºC/W
Package Thermal Resistance,
Junction to Pad RJP On 4-layer PCB based on JEDEC standard 2 ºC/W
*Additional thermal information available on the Allegro website.
Recommended Operating Conditions
Characteristic Symbol Conditions Min. Typ. Max. Units
Supply Voltage VIN 9 – 46 V
Switching Node VLX –0.7 – 46 V
Switching Frequency Range fSW Continuous conduction mode 0.1 – 2.0 MHz
Operating Ambient Temperature TA–40 – 105 ºC
Junction Temperature TJ–40 – 125 ºC
3 A, 2 MHz Buck-Regulating LED Driver
A6210
3
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Reg
Ref
+
–
Control
Logic
On
Timer
Regulator
Comparator
Off
Timer
Driver
Linear
Regulator
Fault
VIN UVLO
TSD
Linear OK
VIN
DIS
GND
TON
BOOT
LX
ISEN
V
IN
24 V
V
IN
Sleep
Circuit
SGND
Switch
Closed = On
NC
C1
1.0 F
C2
L1
68 H
D1
R2
390 m
Blank
Top-off
Charge
Pump
22 nF
R1
180 k
Switching Frequency = 1.4 MHz
All capacitors are X5R or X7R ceramic
Resistor R2 should be surface mount, low inductance type, rated at 250 mW at 70°C
LED1
LED2
LED3
Functional Block Diagram
Pin-out Diagram
Terminal List Table
Number Name Function
1 VIN Input supply
2, 7, 13, 14,
15, 16 NC No connection; tie to GND
3 TON Terminal for on-time setting with external resistor
4, 5, 6 GND Ground terminal
8 ISEN Current sense input
9 SGND Current sense ground reference
10 DIS Disable/enable logic input; active high
11 BOOT Bootstrap supply node
12 LX Switch node
–PAD
Exposed thermal pad; connect to ground plane
(GND) by through-hole vias
12
11
10
9
1
2
3
4
5
6
7
8
16
15
14
13
NC
NC
NC
NC
GND
GND
NC
ISEN
LX
BOOT
DIS
SGND
PAD
VIN
NC
TON
GND
(Top View)
3 A, 2 MHz Buck-Regulating LED Driver
A6210
4
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
ELECTRICAL CHARACTERISTICS* valid at TJ = 25°C, VIN = 9 to 46 V, unless otherwise noted
Characteristic Symbol Conditions Min. Typ. Max. Units
General
VIN Quiescent Current IVINOFF DIS = high, VIN = 46 V – – 100 A
Current Sense Voltage VSENSE 176 183 190 mV
On-Time Tolerance TON Based on selected value –15 – 15 %
Minimum On-Time Period Ton(min) – 50 60 ns
Minimum Off-Time Period Toff(min) – – 350 ns
Start-Up Time tSTART
Using application circuit on page 1; time from
application of ¯
D
¯
¯
I
¯
¯
S
¯
(enable) to reaching target current –15–s
Buck Switch On-Resistance RDS(on) TJ = 25°C, ILOAD = 3 A – 350 – m
TJ = 125°C, ILOAD = 3 A – 550 – m
Input
DIS Input Voltage Threshold VDIS Device enabled – – 1 V
DIS Open-Circuit Voltage VDISOC Device disabled 2 – 7 V
DIS Input Current IIN DIS = 0 V –10 – –1 A
Protection
VIN Undervoltage Shutdown Threshold VINUV Voltage rising 6.3 – 7.5 V
VIN Undervoltage Shutdown Hysteresis VINUV(hys) 0.7 – 1.1 V
Overtemperature Shutdown Threshold TJTSD Temperature rising – 165 – °C
Overtemperature Shutdown Hysteresis TJTSD(hys) Recovery = TJTSD – TJTSD(hys) – 15 – °C
*Specifications over the junction temperature range of –40°C to 125°C are assured by design and characterization.
3 A, 2 MHz Buck-Regulating LED Driver
A6210
5
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Basic Operation
The A6210 is a buck regulator that utilizes valley current mode
control. The on-time is set by the amount of current that flows
into the TON pin. This is determined by the value of the TON
resistor chosen (R1 in the Functional Block diagram) and the
magnitude of the input voltage, VIN. Under a specific set of
conditions, an on-time can be set that then dictates the switching
frequency. This switching frequency remains reasonably con-
stant throughout load and line conditions as the on-time varies
inversely with the input voltage.
At the beginning of the switching cycle, the buck switch is turned
on for a fixed period that is determined by the current flowing
into TON. Once the current comparator trips, a one-shot mono-
stable, the On Timer, is reset, turning off the switch. The current
through the inductor then decays. This current is sensed through
the external sense resistor (R2), and then compared against the
current-demand signal. After the current through the sense resis-
tor decreases to the valley of the current-demand signal, the On
Timer is set to turn the buck switch back on again and the cycle is
repeated.
Disable/Enable The regulator is enabled by pulling the DIS pin
low. To disable the regulator, the DIS pin can simply be discon-
nected (open circuit).
Shutdown The regulator is disabled in the event of either an
overtemperature event, or an undervoltage on VIN (VINUV) or on
an internal housekeeping supply.
As soon as any of the above faults have been removed and
assuming DIS = 0, the output is restored.
Switch On Time and Switching Frequency The switch
on-time effectively determines the operating frequency of the
converter. To minimize the size of the power inductor and input
filtering it is recommended to run with as high a frequency
as possible. The MOSFET drivers are optimized to minimize
switching losses.
An important consideration in selecting the switching frequency
is to ensure that the on time (60 ns) and off time (350 ns) limita-
tions are not reached under extreme conditions:
• the minimum on time occurs at maximum input voltage
• the minimum off time occurs at minimum input voltage
The following table takes into account the above maximum off
time figure and outlines the typical switching frequencies that can
be achieved for a given number of LEDs and input voltage. Note
that it is highly recommended that worst case values are used
when considering any design.
Switching
Frequency
(MHz)
Input Voltage
12 V 24 V 36 V
Quantity
of LEDs
LED
Span
Voltage
(V)
Quantity
of LEDs
LED
Span
Voltage
(V)
Quantity
of LEDs
LED
Span
Voltage
(V)
2.0 1 3.5 2 7.0 3 10.5
1.7 1 3.5 3 10.5 4 14.0
1.0 2 7.0 4 14.0 6 21.0
0.300 3 10.5 6 21.0 9 31.5
The switch on time is programmed by the current flowing into
the TON pin. The current is determined by the input voltage, VIN ,
and the resistor, R1. The on time, Ton
, can be found:
Ton =.
VIN × 2.05 × 1010 10 × 10–9
R1
+
(1)
To calculate the actual switching frequency, fsw
, the Ton from the
above calculation can be used in conjunction with the transfer
function of the converter, as follows:
fSW =.
×
VOUT
+
Vf
VIN
+
Vf
1
Ton
(2)
A simplified approach to selecting the Ton resistor (R1), to
accomplish an approximate switching frequency, can be found
from the following formula:
R1fSW
=.
VIN × 2.05 × 1010
(3)
Figure 1 illustrates a range of switching frequencies that can be
achieved with a given resistor and LED voltage. Each LED is
assumed to have a voltage drop of 3.5 V.
High Brightness LED Driving
The A6210 can be configured as a very simple, low cost, high
brightness LED driver. The solution can drive high brightness
LEDs up to more than 3 A, while achieving very high efficien-
cies, in excess of 90%.
The solution uses valley current mode control. This architecture
is optimized for high switching frequencies, allowing the use
Functional Description
3 A, 2 MHz Buck-Regulating LED Driver
A6210
6
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
of physically small, low value inductors. An output capacitor is
not necessary either to reduce the ripple current or to close the
control loop.
High efficiencies are achieved via drive circuits optimized to
minimize switching losses and the current sense voltage has a
typical voltage drop of only 183 mV. The current in the LED
string can be pulse width modulated (PWM) via the DIS (Dis-
able/Enable) pin. See figure 4.
The actual current control is maintained on the valley of the cur-
rent ripple. The average LED current is the valley level plus half
the inductor ripple current, as shown in figure 2.
To avoid potential mistriggering issues, it is recommended that
the ripple current that flows through the sense resistor (R2) does
not develop a ripple voltage of less than 20 mV.
The average LED current can be found from:
Iav IVALLEY +
=,
2
IRIPPLE
(4)
substituting values:
Iav ton
=,
R2
183 mV
L
V
IN
–V
LED
××
1
2
+
(5)
where:
ton =.
V
IN
+V
f
V
LED
+V
f
×1
f
SW
(6)
Note: Vf is the forward voltage drop of the recirculation diode
and sense resistor (R2). The valley current is determined by the
sense voltage (183 mV) divided by the sense resistor.
Worked example
This example uses the brief specification outlined in the typical
application circuit on page 1. The following information is used
as a starting point:
VIN = 24 V ,
3 LEDs producing VLED = 12 V ,
ILED = 500 mA, and
LED ripple current, IRIPPLE = 60 mA .
The duty cycle can be found initially. Assume the forward voltage
drop of the re-circulation diode is 400 mV, and that the sense
resistor is 183 mV. Then:
D0.39
=.
V
IN
+V
f
V
LED
+V
f==
12 + 0.58
24 + 0.58
(7)
One of the objectives is to maximize the switching frequency to
minimize the inductor value. When driving at very high switching
frequencies, the duty cycle may be limited due to the minimum
Average
LED Current
t
on
+ t
off
= 1/ f
SW
1
/
2
I
RIPPLE
Current
Time
Valley Current
0
t
on
t
off
Figure 2. Current control
Figure 1. Switching frequency versus value of external resistor R1 on the
TON pin.
400
600
800
1000
1200
1400
1600
1800
2000
104105106
Resistor, R1
fSW (kHz)
(kΩ)
1 LED
2 LEDs
3 LEDs
4 LEDs
5 LEDs
3 A, 2 MHz Buck-Regulating LED Driver
A6210
7
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
off-time of 350 ns. A minimum off-time is required to ensure the
bootstrap supply operates correctly. It can be shown that:
fSW =,
t
off
(min)
1 – D
(8)
where toff is 350 ns maximum.
Therefore:
fSW ==.
350 × 10–9 1.4 MHz
1 – 0.51
The ton resistor (R1) value can be found:
R1=
V
LED
× 2.051 × 1010
f
SW
==
12 × 2.051 × 1010
1.4 × 106176 × 103.
(9)
Choose R1 = 180 k.
The inductor (L1) can now be found using the target LED ripple
current of 60 mA:
L1=
(V
IN
– V
LED)
× D
I
RIPPLE
× f
SW
==
(24 – 12) × 0.51
60 × 10–3 × 1.4 × 10672 × 10–6 .
(10)
Choose L1 = 68 H.
The inductor current rating should exceed the average current
plus half of the ripple current. In addition, it is recommended that
a margin of at least 20% be allowed. In this example, the inductor
current rating, IL , should be:
I
L 1.2 × (500 × 10–3 + 60 × 10–3 / 2) = 636 mA .
The valley control current is simply the average LED current
minus half the ripple current. Therefore:
IVALLEY =
I
RIPPLE
==
2
2.
60 × 10–3
500 × 10–3 –470 mA
I
av –
(11)
The sense resistor (R3) value can be found:
R3=
V
SENSE
I
VALLEY
==
183 × 10–3
470 × 10–3 0.36 .
(12)
Choose R3 = 390 m.
The ripple voltage developed across the sense resistor (R2) is
60 mA × 390 m = 23 mV, which is greater than the minimum
required value of 20 mV.
Measured switching waveforms
From figure 3, it can be seen that the average current through
the LED string is 484 mA. This represents an error of 3.2% with
respect to the target current of 500 mA.
3 A, 2 MHz Buck-Regulating LED Driver
A6210
8
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Average
LED Current
494 mA
Figure 4. PWM on DIS pin at 400 Hz: (A) narrow duty cycle, (B) wide duty cycle.
Symbol Parameter Units/Division
Ch1 VLX 5 V
Ch2 ILED 100 mA
t time 1 ms
t
VLX
ILED
t
VLX
ILED
(A) (B)
Average
LED Current
494 mA
Figure 3. Switching voltage versus current through L1 and LED string
Symbol Parameter Units/Division
Ch1 VLX 5 V
Ch2 ILED 100 mA
t time 200 ns
t
VLX
Ch1
Ch2
ILED
LED ripple current
Average LED Current
484 mA
Ch1
Ch2
Ch1
Ch2
3 A, 2 MHz Buck-Regulating LED Driver
A6210
9
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
TON
DIS
PWM or Switch
GNDNC
L
D1
1
47 H
LX
VIN
ISEN
SGND
A 6210
22 nF
R1
910 k
C1
1.0 F
150 m
R2
C2
BOOT
VIN
42 V
R3
910 kLED
Assembly
Average LED current = 1.34 A
Peak to peak current = 200 mA
LED Assembly voltage = 24 V
Switching frequency = 1.0 MHz
Efficiency = 90.5%
Other Application Circuits
Application Circuit 1
Suggested Parts
Name Description Manufacturer - Part Number
C1 1 F, 25V, X5R or X7R ceramic, 1210 Taiyo Yuden, TDK
C2 22 nF, 50V, X5R or X7R ceramic, 0805
D1 3 A, 60 V, Schottky diode
L1 47 H, 1.4 A inductor Taiyo Yuden - NR 8040T 470M
R1, R3 910 k, 1%, 0603
R2 150 m, 1%, 1206
Plot 1. Average current = 1.34 A Plot 2. Peak to peak current = 200 mA
Plot 3. PWM frequency = 10 kHz, maximum duty cycle Plot 4. PWM frequency = 10 kHz, minimum duty cycle
Plot 5. Plot 4 with expanded time scale Plot 6. PWM frequency = 10 kHz, turn off
Channel 1 – Current through inductor and LED Assembly, Channel 2 – Main switching voltage (LX node)
3 A, 2 MHz Buck-Regulating LED Driver
A6210
10
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
LED
Assembly
GNDNC
L
D1
1
22 H
LX
VIN
ISEN
SGND
A 6210
TON
22 nF
R1
310 k
C1
1.0 F
150 m
DIS
PWM or Switch
R2
180 m
R4
C2
BOOT
VIN
24 V
Average LED current = 2.4 A
Peak to peak current = 260 mA
LED Assembly voltage = 15 V
Switching frequency = 1.0 MHz
Efficiency = 94%
Application Circuit 2
Suggested Parts
Name Description Manufacturer - Part Number
C1 1 F, 25V, X5R or X7R ceramic, 1210 Taiyo Yuden, TDK
C2 22 nF, 50V, X5R or X7R ceramic, 0805
D1 3 A, 60 V, Schottky diode
L1 22 H, 2.8 A inductor Coilcraft - MSS1048-223ML
R1 310 k, 1%, 0603
R2 150 m, 1%, 0805
R4 180 m, 1%, 0805
Channel 1 – Current through inductor and LED Assembly, Channel 2 – Main switching voltage (LX node)
Plot 1. Average current = 2.4 A Plot 2. Peak to peak current = 260 mA
Plot 3. PWM frequency = 10 kHz, maximum duty cycle Plot 4. PWM frequency = 10 kHz, minimum duty cycle
Plot 5. Plot 4 with expanded time scale Plot 6. PWM frequency = 10 kHz, turn off
3 A, 2 MHz Buck-Regulating LED Driver
A6210
11
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
Package EU, 16-Contact QFN
0.95
C
SEATING
PLANE
C0.08
17X
16
16
2
1
1
2
16
2
1
A
ATerminal #1 mark area
Coplanarity includes exposed thermal pad and terminals
BExposed thermal pad (reference only, terminal #1
identifier appearance at supplier discretion)
For Reference Only
(reference JEDEC MO-220WGGC)
Dimensions in millimeters
Exact case and lead configuration at supplier discretion within limits shown
C
D
D
C
Reference land pattern layout (reference IPC7351
QFN65P400X400X80-17W2M)
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)
4.10
0.35
0.65
4.10
0.65
0.75 ±0.050.30 ±0.05
0.40 ±0.10
2.70
2.70
4.00 ±0.15
4.00 ±0.15 2.70
2.70
B
PCB Layout Reference View
3 A, 2 MHz Buck-Regulating LED Driver
A6210
12
Allegro MicroSystems, Inc.
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
For the latest version of this document, visit our website:
www.allegromicro.com
Copyright ©2008-2011, Allegro MicroSystems, Inc.
Allegro MicroSystems, Inc. reserves the right to make, from time to time, such de par tures from the detail spec i fi ca tions as may be required to per-
mit improvements in the per for mance, 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 life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The in for ma tion in clud ed herein is believed to be ac cu rate and reliable. How ev er, Allegro MicroSystems, Inc. assumes no re spon si bil i ty for its use;
nor for any in fringe ment of patents or other rights of third parties which may result from its use.
Revision History
Revision Revision Date Description of Revision
Rev. 2 May 2, 2011 Minor edit
