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Teilenummer | A6210 |
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Beschreibung | 3A 2MHz Buck-Regulating LED Driver | |
Hersteller | Allegro MicroSystems | |
Logo | ||
Gesamt 12 Seiten A6210
3 A, 2 MHz Buck-Regulating LED Driver
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 μA
▪ Thermal shutdown
▪ Supplied in a thermally-enhanced 4 mm QFN package
Applications:
▪ High brightness LEDs
▪ LED driver modules, power supplies and lamps, such as
MR16 and MR11
Package 16-contact QFN (suffix EU):
4 mm × 4 mm × 0.75 mm
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
VIN
24 V
R1
150 kΩ
C1
1.0 μF
Typical Application
VIN BOOT
LX
TON A 6210
ISEN
PWM or Switch
DIS
SGND
NC GND
C2
22 nF
L1
68 μH
D1
R2
390 mΩ
LED1
LED2
LED3
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%
Suggested Parts
Name Description
C1 1 μF, 25V, X5R or X7R ceramic, 1210
C2 22 nF, 50V, X5R or X7R ceramic, 0805
D1 1 A, 30 V, Schottky diode
L1 68 μH, 1 A inductor
R1 180 kΩ, 1%, 0805
R2 390 mΩ, 1%, 0805
Manufacturer - Part Number
Taiyo Yuden, TDK
Taiyo Yuden - NR 6045T 680M
A6210
3 A, 2 MHz Buck-Regulating LED Driver
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 +
IRIPPLE
2
substituting values:
,
(4)
where:
Iav =
183 mV
R2
+
1
2
×
VIN
–VLED
L
×
ton
,
(5)
ton =
VLED +Vf
VIN +Vf
×
1
fSW
.
(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:
D
=
VLED +Vf
VIN +Vf
=
12 + 0.58
24 + 0.58
=
0.39
.
(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
2000
1800
1600
1400
1200
1000
800
600
400
104
1 LED
2 LEDs
3 LEDs
4 LEDs
5 LEDs
105
Resistor, R1 (kΩ)
106
Figure 1. Switching frequency versus value of external resistor R1 on the
TON pin.
ton + toff = 1/ fSW
ton toff
Valley Current
0
Time
Figure 2. Current control
1/2 IRIPPLE
Average
LED Current
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
6 Page A6210
3 A, 2 MHz Buck-Regulating LED Driver
Revision History
Revision
Rev. 2
Revision Date
May 2, 2011
Description of Revision
Minor edit
Copyright ©2008-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, 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 information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
12 Page | ||
Seiten | Gesamt 12 Seiten | |
PDF Download | [ A6210 Schematic.PDF ] |
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