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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 A Thermal shutdown Supplied in a thermally-enhanced 4 mm QFN package
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 x 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.
Applications:
High brightness LEDs LED driver modules, power supplies and lamps, such as MR16 and MR11
Package 16-contact QFN (suffix EU):
4 mm x 4 mm x 0.75 mm
Typical Application
VIN 24 V
R1 150 k C1 1.0 F VIN
BOOT
LX
C2 22 nF
L1 68 H
TON
A 6210
D1 ISEN R2 390 m
LED1
LED2
PWM or Switch DIS NC GND SGND
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 C1 C2 D1 L1 R1 R2 Description 1 F, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 1 A, 30 V, Schottky diode 68 H, 1 A inductor 180 k, 1%, 0805 390 m, 1%, 0805 Manufacturer - Part Number Taiyo Yuden, TDK
Taiyo Yuden - NR 6045T 680M
6210-DS, Rev. 1
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Selection Guide
Part Number
A6210GEUTR-T
Packing
1500 pieces per reel
Package
16-contact 4 mm x 4 mm QFN with exposed thermal pad
Absolute Maximum Ratings (reference to GND)
Characteristic VIN Pin Supply Voltage LX Pin Switching Node Voltage ISEN Pin Current Sense Voltage DIS Pin Disable Voltage TON Pin On-Time Voltage Operating Ambient Temperature Maximum Junction Temperature Storage Temperature Symbol VIN VLX VISEN VDIS VTON TA TJ(max) Tstg Range G Notes Rating -0.3 to 50 -1 to 50 -1.0 to 0.5 -0.3 to 7 -0.3 to 50 -40 to 105 150 -55 to 150 Units V V V V V C C C
Recommended Operating Conditions
Characteristic Supply Voltage Switching Node Switching Frequency Range Operating Ambient Temperature Junction Temperature Symbol VIN VLX fSW TA TJ Continuous conduction mode Conditions Min. 9 -0.7 0.1 -40 -40 Typ. - - - - - Max. 46 46 2.0 105 125 Units V V MHz C C
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
RJA RJP
Test Conditions*
On 4-layer PCB based on JEDEC standard On 4-layer PCB based on JEDEC standard
Value
36 2
Units
C/W C/W
*Additional thermal information available on the Allegro website.
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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A6210
3 A, 2 MHz Buck-Regulating LED Driver
Functional Block Diagram
VIN 24 V
C1 1.0 F VIN Linear Regulator R1 180 k Sleep Circuit Driver TON BOOT Top-off Charge Pump
C2 22 nF
VIN
LX
L1 68 H
LED1
D1 On Timer Off Timer Control Logic Blank ISEN R2 390 m
LED2
LED3
DIS Switch Closed = On
Regulator Comparator
VIN UVLO Linear OK TSD Fault
+ -
SGND
Reg Ref
NC
GND
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 70C
Terminal List Table
Number Name VIN NC TON GND ISEN SGND DIS BOOT LX PAD Input supply No connection; tie to GND Terminal for on-time setting with external resistor Ground terminal Current sense input Current sense ground reference Disable/enable logic input; active high Bootstrap supply node Switch node Exposed thermal pad; connect to ground plane (GND) by through-hole vias Function
Pin-out Diagram
16 NC 15 NC 14 NC 13 NC
1 2, 7, 13, 14, 15, 16 3 4, 5, 6 8 9 10 11 12 -
VIN NC TON GND
1 2 3 4 5 6 7 8 PAD
12 LX 11 BOOT 10 DIS 9 SGND
(Top View)
ISEN
GND
GND
NC
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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A6210
3 A, 2 MHz Buck-Regulating LED Driver
ELECTRICAL CHARACTERISTICS* valid at TJ = 25C, VIN = 9 to 46 V, unless otherwise noted
Characteristic General VIN Quiescent Current Current Sense Voltage On-Time Tolerance Minimum On-Time Period Minimum Off-Time Period Start-Up Time Buck Switch On-Resistance Input DIS Input Voltage Threshold DIS Open-Circuit Voltage DIS Input Current Protection VIN Undervoltage Shutdown Threshold VIN Undervoltage Shutdown Hysteresis Overtemperature Shutdown Threshold Overtemperature Shutdown Hysteresis
*Specifications
Symbol IVINOFF VSENSE TON Ton(min) Toff(min) tSTART RDS(on)
Conditions DIS = high, VIN = 46 V Based on selected value
Min. - 176 -15 - -
Typ. - 183 - 50 - 15 350 550 - - - - - 165 15
Max. 100 190 15 60 350 - - - 1 7 -1 7.5 1.1 - -
Units A mV % ns ns s m m V V A V V C C
Using application circuit on page 1; time from IS application of (enable) to reaching target current D TJ = 25C, ILOAD = 3 A TJ = 125C, ILOAD = 3 A Device enabled Device disabled DIS = 0 V Voltage rising Temperature rising Recovery = TJTSD - TJTSD(hys)
- - - - 2 -10 6.3 0.7 - -
VDIS VDISOC IIN VINUV VINUV(hys) TJTSD TJTSD(hys)
over the junction temperature range of -40C to 125C are assured by design and characterization.
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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A6210
3 A, 2 MHz Buck-Regulating LED Driver
Functional Description
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 constant 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 monostable, 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 resistor 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 disconnected (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) limitations are not reached under extreme conditions: * the minimum on time occurs at maximum input voltage * the maximum 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.
Input Voltage Switching Frequency (MHz) 12 V 24 V LED Span Voltage (V) 7.0 10.5 14.0 21.0 36 V Quantity of LEDs 3 4 6 9 LED Span Voltage (V) 10.5 14.0 21.0 31.5 LED Quantity Span Quantity of LEDs Voltage of LEDs (V) 1 1 2 3 3.5 3.5 7.0 10.5 2 3 4 6
2.0 1.7 1.0 0.300
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: R1 Ton = + 10 x 10-9 . VIN x 2.05 x 1010 (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 = 1 VOUT + Vf x VIN + Vf Ton . (2)
A simplified approach to selecting the Ton resistor (R1), to accomplish an approximate switching frequency, can be found from the following formula: R1 = VIN x 2.05 x 1010 fSW . (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 efficiencies, in excess of 90%. The solution uses valley current mode control. This architecture is optimized for high switching frequencies, allowing the use
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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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 (Disable/Enable) pin. See figure 4. The actual current control is maintained on the valley of the current 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 substituting values: Iav = where: ton VLED +Vf 1 = V +V x fSW IN f . (6) 183 mV 1 VIN -VLED x ton + x 2 L R2 , (5) IRIPPLE = IVALLEY + 2 , (4)
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: VLED +Vf 12 + 0.58 0.39 D= VIN +Vf = 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
2000 1800 1600
fSW (kHz)
ton + toff = 1/ fSW
1 LED 2 LEDs 3 LEDs 4 LEDs 5 LEDs
ton
toff
1/ I 2 RIPPLE
1200 1000
Current
1400
Valley Current
800 600 400 104
Average LED Current
0 Time
105 Resistor, R1 (k) 106
Figure 1. Switching frequency versus value of external resistor R1 on the TON pin.
Figure 2. Current control
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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A6210
3 A, 2 MHz Buck-Regulating LED Driver
off-time of 350 ns. A minimum off-time is required to ensure the bootstrap supply operates correctly. It can be shown that: 1-D fSW = toff (min) where toff is 350 ns maximum. Therefore: fSW 1 - 0.51 = 350 x 10-9 = 1.4 MHz (8)
a margin of at least 20% be allowed. In this example, the inductor current rating, IL , should be: IL 1.2 x (500 x 10-3 + 60 x 10-3 / 2) = 636 mA . The valley control current is simply the average LED current minus half the ripple current. Therefore: IVALLEY = Iav - IRIPPLE 2 60 x 10-3 = 470 mA 2 . (11)
,
.
= 500 x 10-3 - (9)
The ton resistor (R1) value can be found: VLED x 2.051 x 1010 fSW 12 x 2.051 x 1010 = = 176 x 103 . 1.4 x 106 Choose R1 = 180 k. R1 =
The sense resistor (R3) value can be found: R3 = VSENSE IVALLEY 183 x 10-3 = = 0.36 470 x 10-3 (12) .
The inductor (L1) can now be found using the target LED ripple current of 60 mA: (V - VLED) x D L1 = IN IRIPPLE x fSW (24 - 12) x 0.51 = 72 x 10-6 . = 60 x 10-3 x 1.4 x 106 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 (10)
Choose R3 = 390 m. The ripple voltage developed across the sense resistor (R2) is 60 mA x 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.
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
7
A6210
3 A, 2 MHz Buck-Regulating LED Driver
ILED
LED ripple current 484 mA
Ch1
VLX
Average LED Current
Ch2 t
Symbol Ch1 Ch2 t
Parameter VLX ILED time
Units/Division 5V 100 mA 200 ns
Figure 3. Switching voltage versus current through L1 and LED string
ILED
ILED 494 mA 494 mA
Average LED Current VLX
Ch1 Ch2
Average LED Current
Ch1 Ch2
VLX
t
t
(A)
Symbol Ch1 Ch2 t Parameter VLX ILED time Units/Division 5V 100 mA 1 ms
(B)
Figure 4. PWM on DIS pin at 400 Hz: (A) narrow duty cycle, (B) wide duty cycle.
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
8
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Other Application Circuits Application Circuit 1
VIN 42 V
C1 1.0 F R1 910 k R3 910 k
VIN
BOOT
LX
C2 22 nF
L1 47 H
Suggested Parts Name Description 1 F, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 3 A, 60 V, Schottky diode 47 H, 1.4 A inductor 910 k, 1%, 0603 150 m, 1%, 1206 Manufacturer - Part Number Taiyo Yuden, TDK
A 6210
TON ISEN
D1
LED Assembly
PWM or Switch DIS SGND GND
R2 150 m
C1 C2 D1 L1 R1, R3 R2
Taiyo Yuden - NR 8040T 470M
NC
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%
Channel 1 - Current through inductor and LED Assembly, Channel 2 - Main switching voltage (LX node)
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
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
9
A6210
3 A, 2 MHz Buck-Regulating LED Driver
Application Circuit 2
VIN 24 V
C1 1.0 F R1 310 k
VIN
BOOT
LX
C2 22 nF
L1 22 H
Suggested Parts Name Description 1 F, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 3 A, 60 V, Schottky diode 22 H, 2.8 A inductor 310 k, 1%, 0603 150 m, 1%, 0805 180 m, 1%, 0805 Manufacturer - Part Number Taiyo Yuden, TDK
A 6210
TON ISEN
D1
LED Assembly
PWM or Switch DIS SGND GND
R2 150 m
R4 180 m
C1 C2 D1 L1 R1 R2 R4
Coilcraft - MSS1048-223ML
NC
Average LED current = 2.4 A Peak to peak current = 260 mA LED Assembly voltage = 15 V Switching frequency = 1.0 MHz Efficiency = 94%
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
Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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A6210
3 A, 2 MHz Buck-Regulating LED Driver
Package EU, 16-Contact QFN
0.35 4.00 0.15 16 1 2 A 4.00 0.15 0.95 1 2 2.70 4.10 16 0.65
2.70 4.10 17X D 0.08 C 0.30 0.05 0.65 SEATING PLANE 0.75 0.05 C C PCB Layout Reference View
For Reference Only (reference JEDEC MO-220WGGC) Dimensions in millimeters Exact case and lead configuration at supplier discretion within limits shown A Terminal #1 mark area B Exposed thermal pad (reference only, terminal #1 identifier appearance at supplier discretion)
0.40 0.10 B 2 1 2.70
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) D Coplanarity includes exposed thermal pad and terminals
16 2.70
Copyright (c)2008-2009, Allegro MicroSystems, Inc. The products described here are manufactured under one or more U.S. patents or U.S. patents pending. Allegro MicroSystems, Inc. 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, Inc. 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, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com
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