A6210 3 A, 2 MHz Buck-Regulating LED Driver Features and Benefits Description ▪ 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 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. Applications: ▪ High brightness LEDs ▪ LED driver modules, power supplies and lamps, such as MR16 and MR11 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. Package 16-contact QFN (suffix EU): 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. 4 mm × 4 mm × 0.75 mm Typical Application VIN 24 V R1 150 kΩ BOOT VIN C1 1.0 μF C2 22 nF L1 68 μH LX TON D1 A 6210 ISEN LED2 R2 390 mΩ PWM or Switch DIS 6210-DS, Rev. 1 LED3 SGND NC 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% LED1 GND Suggested Parts Name C1 C2 D1 L1 R1 R2 Description Manufacturer - Part Number 1 μF, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 1 A, 30 V, Schottky diode 68 μH, 1 A inductor 180 kΩ, 1%, 0805 390 mΩ, 1%, 0805 Taiyo Yuden, TDK Taiyo Yuden - NR 6045T 680M 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 × 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 Symbol Notes Rating Units –0.3 to 50 V VLX –1 to 50 V VISEN –1.0 to 0.5 V VIN DIS Pin Disable Voltage VDIS –0.3 to 7 V TON Pin On-Time Voltage VTON –0.3 to 50 V Operating Ambient Temperature TA –40 to 105 ºC Maximum Junction Temperature TJ(max) 150 ºC Tstg –55 to 150 ºC Storage Temperature Range G Recommended Operating Conditions Min. Typ. Max. Supply Voltage Characteristic Symbol VIN Conditions 9 – 46 Units V Switching Node VLX –0.7 – 46 V Switching Frequency Range fSW 0.1 – 2.0 MHz Operating Ambient Temperature TA –40 – 105 ºC Junction Temperature TJ –40 – 125 ºC Continuous conduction mode Thermal Characteristics may require derating at maximum conditions, see application information Characteristic Symbol Package Thermal Resistance, Junction to Ambient RθJA Package Thermal Resistance, Junction to Pad RθJP Test Conditions* Value Units On 4-layer PCB based on JEDEC standard 36 ºC/W On 4-layer PCB based on JEDEC standard 2 ºC/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 2 A6210 3 A, 2 MHz Buck-Regulating LED Driver Functional Block Diagram VIN 24 V C2 22 nF C1 1.0 μF BOOT VIN Top-off Charge Pump Linear Regulator VIN Sleep Circuit R1 180 kΩ L1 68 μH LX LED1 Driver D1 TON On Timer Control Logic Off Timer LED3 ISEN Blank DIS R2 390 mΩ Regulator Comparator Switch Closed = On LED2 SGND VIN UVLO Linear OK + Fault TSD Reg Ref – GND NC 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 Terminal List Table VIN 1 13 NC 14 NC 15 NC 16 NC Pin-out Diagram 12 LX NC 2 TON 3 10 DIS GND 4 9 11 BOOT 8 ISEN 7 NC 6 GND GND 5 PAD (Top View) Number Name 1 VIN Input supply Function 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 SGND 10 DIS 11 BOOT 12 LX – PAD Disable/enable logic input; active high Bootstrap supply node Switch node Exposed thermal pad; connect to ground plane (GND) by through-hole vias Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 3 A6210 3 A, 2 MHz Buck-Regulating LED Driver ELECTRICAL CHARACTERISTICS* valid at TJ = 25°C, VIN = 9 to 46 V, unless otherwise noted Characteristic Symbol Conditions Min. Typ. Max. Units – – 100 μA General VIN Quiescent Current IVINOFF Current Sense Voltage VSENSE On-Time Tolerance ∆TON DIS = high, VIN = 46 V Based on selected value 176 183 190 mV –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 D̄¯¯¯IS̄¯ (enable) to reaching target current – 15 – μs Buck Switch On-Resistance RDS(on) TJ = 25°C, ILOAD = 3 A – 350 – mΩ TJ = 125°C, ILOAD = 3 A – 550 – mΩ VDIS Device enabled – – 1 V VDISOC Device disabled 2 – 7 V DIS = 0 V –10 – –1 μA Voltage rising 6.3 – 7.5 V 0.7 – 1.1 V Temperature rising – 165 – °C Recovery = TJTSD – TJTSD(hys) – 15 – °C Input DIS Input Voltage Threshold DIS Open-Circuit Voltage DIS Input Current IIN Protection VIN Undervoltage Shutdown Threshold VINUV VIN Undervoltage Shutdown Hysteresis VINUV(hys) Overtemperature Shutdown Threshold TJTSD Overtemperature Shutdown Hysteresis TJTSD(hys) *Specifications over the junction temperature range of –40°C to 125°C 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 4 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: 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 Quantity Span Quantity of LEDs Voltage of LEDs (V) 36 V 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: R1 Ton = + 10 × 10–9 . VIN × 2.05 × 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 × 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 × 2.05 × 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. • the maximum off time occurs at minimum input voltage 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 following table takes into account the above maximum off time figure and outlines the typical switching frequencies that can The solution uses valley current mode control. This architecture is optimized for high switching frequencies, allowing the use • the minimum on time occurs at maximum input voltage Allegro MicroSystems, Inc. 115 Northeast Cutoff Worcester, Massachusetts 01615-0036 U.S.A. 1.508.853.5000; www.allegromicro.com 5 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. 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: 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. VIN = 24 V , 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. ILED = 500 mA, and The average LED current can be found from: Iav IRIPPLE = IVALLEY + 2 (4) , 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: substituting values: Iav = 3 LEDs producing VLED = 12 V , 183 mV 1 VIN –VLED × ton + × L R2 2 (5) , VLED +Vf 12 + 0.58 0.39 D= VIN +Vf = 24 + 0.58 = where: ton VLED +Vf 1 = V +V × f IN f SW . (7) One of the objectives is to maximize the switching frequency to (6) . minimize the inductor value. When driving at very high switching frequencies, the duty cycle may be limited due to the minimum 2000 ton + toff = 1/ fSW 1800 1400 1 LED 2 LEDs ton toff 1/ I 2 RIPPLE 4 LEDs Current fSW (kHz) 1600 3 LEDs 5 LEDs 1200 1000 Valley Current 800 0 600 400 104 Average LED Current Time 105 106 Resistor, R1 (kΩ) 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 6 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) (8) , where toff is 350 ns maximum. a margin of at least 20% be allowed. In this example, the inductor current rating, IL , should be: IL ≥ 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: Therefore: fSW 1 – 0.51 = 350 × 10–9 = 1.4 MHz IVALLEY = Iav – . = 500 × 10–3 – The ton resistor (R1) value can be found: VLED × 2.051 × 1010 fSW 12 × 2.051 × 1010 = = 176 × 103 . 1.4 × 106 Choose R1 = 180 kΩ. R1 = (9) (11) 60 × 10–3 = 470 mA 2 . The sense resistor (R3) value can be found: VSENSE IVALLEY 183 × 10–3 = = 0.36 470 × 10–3 (12) R3 = The inductor (L1) can now be found using the target LED ripple current of 60 mA: (V – VLED) × D L1 = IN IRIPPLE × fSW (24 – 12) × 0.51 = 72 × 10–6 . = 60 × 10–3 × 1.4 × 106 IRIPPLE 2 (10) Choose L1 = 68 μH. The inductor current rating should exceed the average current plus half of the ripple current. In addition, it is recommended that . Choose R3 = 390 mΩ. The ripple voltage developed across the sense resistor (R2) is 60 mA × 390 mΩ = 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 LED ripple current ILED 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 Average LED Current Ch1 Ch2 VLX Ch1 Ch2 t VLX t (A) (B) Symbol Ch1 Ch2 t Parameter VLX ILED time Units/Division 5V 100 mA 1 ms 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 μF R1 910 kΩ BOOT VIN C2 22 nF L1 47 μH LX R3 910 kΩ A 6210 Name D1 LED Assembly ISEN TON R2 150 mΩ PWM or Switch DIS NC Suggested Parts SGND GND C1 C2 D1 L1 R1, R3 R2 Description Manufacturer - Part Number 1 μF, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 3 A, 60 V, Schottky diode 47 μH, 1.4 A inductor 910 kΩ, 1%, 0603 150 mΩ, 1%, 1206 Taiyo Yuden, TDK Taiyo Yuden - NR 8040T 470M 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 BOOT VIN C1 1.0 μF C2 22 nF L1 22 μH LX R1 310 kΩ A 6210 Name D1 R2 150 mΩ PWM or Switch NC LED Assembly ISEN TON DIS Suggested Parts R4 180 mΩ SGND GND C1 C2 D1 L1 R1 R2 R4 Description Manufacturer - Part Number 1 μF, 25V, X5R or X7R ceramic, 1210 22 nF, 50V, X5R or X7R ceramic, 0805 3 A, 60 V, Schottky diode 22 μH, 2.8 A inductor 310 kΩ, 1%, 0603 150 mΩ, 1%, 0805 180 mΩ, 1%, 0805 Taiyo Yuden, TDK Coilcraft - MSS1048-223ML 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 10 A6210 3 A, 2 MHz Buck-Regulating LED Driver Package EU, 16-Contact QFN 0.35 4.00 ±0.15 1 0.65 16 16 0.95 A 1 2 2 4.00 ±0.15 2.70 4.10 2.70 4.10 17X D SEATING PLANE 0.08 C 0.30 ±0.05 0.75 ±0.05 0.65 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 2.70 2 1 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 ©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 11