Green AL8400 /AL8400Q LINEAR LED DRIVER-CONTROLLER with 200mV CURRENT SENSE VOLTAGE and AUTOMOTIVE GRADE Description Pin Assignments The AL8400 is a 5-terminal adjustable Linear LED driver-controller offering excellent temperature stability and output handling capability. The AL8400 simplifies the design of linear and isolated LED drivers. With its low 200mV current sense FB pin, it controls the regulation of LED current with minimal power dissipation when compared to traditional linear LED drivers. This makes it ideal for medium to high current LED driving. The AL8400 open-collector output can operate from 0.2V to 18V enabling it to drive external MOSFET and Bipolar transistors. This enables the MOSFET and Bipolar selection to be optimized for the chosen application. It also provides the capability to drive longer LED chains, by tapping VCC from the chain, where the chain voltage may exceed 18V. Features • Low Reference Voltage (VFB = 0.2V) • -40 to +125°C Temperature Range The AL8400Q is Automotive Grade and is AEC-Q100 Grade 1 • 3% Reference Voltage Tolerance at +25°C qualified. • Low Temperature Drift • 0.2V to 18V Open-Collector Output • High Power Supply Rejection: It is available in the space saving low profile SOT353 package. Applications (> 45dB at 300kHz) • Isolated Offline LED Lamps • • Linear LED Driver • • LED Signs Lead-Free Finish; RoHS Compliant (Notes 1 & 2) • Instrumentation Illumination Halogen and Antimony Free. “Green” Device (Note 3) Notes: AL8400QSE-7 Automotive Grade qualified to AEC-Q100 Grade 1 SOT353: Available in “Green” Molding Compound (No Br, Sb) 1. EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant. All applicable RoHS exemptions applied. 2. See http://www.diodes.com for more information about Diodes Incorporated’s definitions of Halogen- and Antimony-free, "Green" and Lead-free. 3. Halogen- and Antimony-free "Green” products are defined as those which contain <900ppm bromine, <900ppm chlorine (<1500ppm total Br + Cl) and <1000ppm antimony compounds. Typical Applications Circuit Vcc RB 3 Vcc OUT 5 CD AL8400 Q2 FB GND GND 2 E1 1 4 CL RSET ILED = VREF/RSET AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 1 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Pin Descriptions Pin Number 1 2 3 4 5 Name E1 GND VCC FB OUT Function Emitter Connection. Connect to GND. Analog Ground. Ground return for reference and amplifier. Connect to E1. Supply Input. Connect a 0.47μF ceramic capacitor close to the device from VCC to GND. Feedback Input. Regulates to 200mV nominal. Output. Connect a capacitor close to device between OUT and GND. See the Applications Information section. Functional Block Diagram Figure 1 Block Diagram Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.) Symbol VCC VOUT VFB VE1 TJ TST Parameter Supply Voltage Relative to GND OUT Voltage Relative to GND FB Voltage Relative to GND E1 Voltage Relative to GND Operating Junction Temperature Storage Temperature Rating 20 20 20 -0.3 to+0.3 -40 to 150 -55 to 150 Unit V V V V °C °C These are stress ratings only. Operation outside the absolute maximum ratings may cause device failure. Operation at the absolute maximum rating for extended periods may reduce device reliability. Package Thermal Data Package θJA SOT353 400°C/W AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 PDIS TA = +25°C, TJ = +150°C 310mW 2 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Symbol VCC VOUT IOUT TA Parameter Supply Voltage Range OUT Voltage Range OUT Pin Current Operating Ambient Temperature Range Min 2.2 0.2 0.3 -40 Max 18 18 15 +125 Units V mA °C Electrical Characteristics (Note 4) (@TA = +25°C, VCC= 12V, VOUT = VFB, IOUT = 1mA, unless otherwise specified.) Symbol VFB Parameter Conditions Feedback Voltage FBLOAD Feedback Pin Load Regulation IOUT = 1 to 15mA FBLINE Feedback Pin Line Regulation VCC = 2.2V to 18V FBOVR Output Voltage Regulation VOUT = 0.2V to 18V, IOUT =1mA (Ref. Figure 1) IFB FB Input Bias Current VCC = 18V ICC Supply Current VCC = 2.2V to 18V, IOUT =10mA OUT Leakage Current VCC = 18V, VOUT = 18V, VFB =0V Dynamic Output Impedance IOUT = 1 to 15mA, f < 1kHz Power Supply Rejection Ratio f = 300kHz, VAC = 0.3VPP IOUT(LK) ZOUT PSRR BW G Note: Min Typ Max TA = +25°C 0.194 0.2 0.206 TA = -40°C to +125°C 0.190 TA = +25°C 0.210 3.1 TA = -40°C to +125°C 6 10 TA = +25°C 0.1 1.5 TA = -40°C to +125°C 2 TA = +25°C 2 TA = -40°C to +125°C 3 TA = +25°C -45 TA = -40°C to +125°C TA = +25°C -200 0 0.48 1 TA = -40°C to +125°C 1.5 TA = +25°C 0.1 TA = +125°C 1 TA = +25°C 0.25 TA = -40°C to +125°C 0.4 0.6 Units V mV mV mV nA mA µA Ω TA = +25°C 45 dB Amplifier Unity Gain Frequency TA = +25°C 600 kHz Amplifier Transconductance TA = +25°C 4500 mA/V 4. Production testing of the device is performed at +25°C. Functional operation of the device and parameters specified over the operating temperature range are guaranteed by design, characterization and process control. Typical Characteristics Line Regulation Load Regulation AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 3 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Typical Characteristics (cont.) Supply Current with Input Voltage Supply Current with Load Current FB Voltage Change with Temperature FB Input Current with Temperature Bipolar Transistor Driving MOSFET Driving AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 4 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information Description The AL8400 Linear LED driver controller uses an external pass element to drive the LEDs and uses its FB pin to sense the LED current through an external resistor RSET. The pass element is driven by the AL8400’s open collector OUT pin which allows the pass element to be either an NPN transistor or N-channel MOSFET. An external pull-up resistor, RB, is required to be connected from the OUT pin to VCC. This resistor supplies the output bias current of the AL8400 together with any current which the pass element requires. In order to maintain the accuracy of the 200mV reference voltage on the FB pin the value of RB should be set so that the OUT pin sinks 1mA. Stability As with all ICs, for best stability a 0.1µF minimum (X7R ceramic) power supply decoupling capacitor, CD, connected between VCC and Ground (See Figure 2) is recommended. CD should be placed as close to the VCC pin as possible < 5mm. Figure 2 Application Circuit Using Bipolar Transistor The AL8400 requires an output capacitor, CL in Figure 2, to be connected from the OUT pin to Ground. This capacitor is required to compensate the current control loop of the AL8400. This compensation capacitor must be placed as close to the OUT pin as possible < 5mm. If the PCB traces are too long, there is the possibility of oscillation at about 5MHz. The capacitors CD and CL must be mounted immediately adjacent to the AL8400, with direct connections to OUT, E1, GND and VCC. The limit of 5mm provides a good margin for stability. The value of capacitor CL is determined from the value of the pull-up resistor RB so that: CL x RB ≥ 2ms For example if RB = 1kΩ, then CL must be 2µF or greater. The recommended capacitor type is X7R ceramic. 200 225 V OUT = 0.6V VOUT = 0.6V = 2.2uF =OUT 1kΩ R C B 180 CL = 2.2µF 100 135 50 90 0 Phase (deg) Gain (dB) 150 45 Gain Phas e -50 0 1 10 100 1k 10k 100k 1M Frequency (Hz) Figure 3 Gain and Phase vs. Frequency with RB = 1kΩ and CL = 2.2µF AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 5 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) Bipolar Transistor as the Pass Element For driving currents in the region of about 50mA to about 400mA, the recommended NPN is DNLS320E in the SOT223 package. The high DC current gain of the DNLS320E is useful in this application, in order to minimize the current in RB. The design procedure is as follows, referring to Figure 4. Figure 4 Application Circuit Using Bipolar Transistor There are two important equations for the circuit: LED Circuit Path: 1. VCC = (VLED + VCE + VFB) where VFB is approximately the internal reference voltage of 200mV. The maximum total LED voltage plus the reference voltage determines the minimum supply voltage. Substituting into equation 1 yields: VCC min = VLED max + VCEsat + VFB where VLEDmax is the maximum LED chain voltage. Control Drive Circuit Path 2. VCC = (VRB + VBE + VFB) For a bipolar transistor the voltage (VRB) across bias resistor RB consists of the base current of Q2 and the output current of the AL8400. So rearranging equation 2 yields the boundaries for allowable RB values: 3. R B max = VCC min − VBE max − VFB IOUT min + IB max where IBmax is the maximum transistor base current IB max = 4. R B min = where IBmin is the minimum transistor base current ILED hFE min IB min = where hFEmin is the minimum DC current gain of the transistor. VCC max − VBE min − VFB IOUT max + IB min ILED hFE max where hFEmax is the maximum DC current gain of the transistor. The value of RB should be set somewhere between RBmax and RBmin with the target of trying to get IOUT of the AL8400 close to 1mA for nominal conditions. Once RB has been determined the value for compensation capacitor, CL, should be calculated. CL ≈ 2ms RB Finally, the bipolar selection is also influenced by the maximum power dissipation PTOT = ILED x (VCC – VLED – VREF) = ILED x VCE Since this determines the package choice (θJA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT x θJA where TJ(MAX) is the maximum operating junction temperature, TA is the ambient temperature, θJA is the junction to ambient thermal resistance. AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 6 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) Bipolar Example – Choosing RB and CL The driver is required to control 3 series connected LEDs at 150mA ±10% from a 12V ±5% supply. Each LED has a forward voltage of 3V minimum and of 3.6V maximum. From this information the minimum supply voltage is 11.4V and the maximum LED chain voltage is 10.8V. Rearranging equation 1 (page 7); the minimum voltage drop across the bipolar transistor is determined to be: VCE = VCC min − VLED max − VFB = 11.4 V − 10.8 V − 0.2V = 0.4 V We will use the DNLS320E bipolar transistor (Q2.) RBmax The DNLS320E datasheet table states: VCE(SAT)max = 0.1V at IC = 100mA, IB = 0.5mA hFEmin = 500 @ IC = 100mA, VCE = 2V; The datasheet graph (see left) shows a very slow variation at 100mA, so a value of 500 is considered appropriate. Then IB max = 150mA = 0.3mA 500 The minimum recommended IOUT for AL8400 is 0.3mA and the maximum VBE, according to the DNLS320E datasheet graph (Figure 6), is approximately 0.8V at -55°C. From these and equation 3, the maximum allowed bias resistor value is: VCC min − VBE max − VFB = IOUT min + IB max R B max = = 11.4 − 0.8 − 0.2 0.0003 + 0.0003 = 17.3kΩ Figure 6 DNLS320E VBE vs. IC Figure 5 DNLS320E HFE vs. IC AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 7 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) Bipolar Example – Choosing RB and CL (cont.) RBmin To ensure that the output capability of the AL8400 is not exceeded at maximum VIN, maximum hFE and minimum VBE, these values should be substituted back into the RB equation to determine the minimum allowable value for RB. hFEmax is about 1200 @ IC = 100mA, and a temperature of +85°C (Figure 5) which results in: IB min = 150 = 0.125mA 1200 The maximum recommended IOUT for AL8400 is 15mA.The minimum VBE, according to the DNLS320E datasheet graph (Figure 6), is approximately 0.4V at 85°C and assuming VCCmax = 12.6V, then from equation 4 the bias resistor value is: RB min = = VCC max − VBE min − VFB = IOUT max + IB min 8.4 − 0.4 − 0.2 = 516Ω this is less than 17kΩ and so the AL8400 output current is within its ratings. 0.015 + 0.000125 CL Choosing RB = 11kΩ satisfies the requirements for the AL8400 conformance and sets approximately 1mA in the OUT pin. The required compensation capacitor can therefore be calculated from: CL ≈ 2ms ≈ 0.18μF Æ 180nF 11kΩ The value of RSET is VREF/ILED so: RSET = 0.2/0.15 = 1.333Ω Î Choosing two 2.7Ω yields 1.35Ω giving an approximate 1.3% difference from target. Finally, the maximum power dissipation of the external bipolar transistor is: PTOT = ILED x VCEMAX = ILED x (VCC_max – VLED_MIN – VFB) = 0.51W This determines the package choice (θJA) in order to keep the junction temperature of the bipolar transistor below the maximum value allowed. At a maximum ambient temperature of +60°C the junction temperature becomes TJ = TA + PTOT x θJA = 60 + 0.51 x 125 = +123.75°C N-Channel MOSFET as the Pass Element Alternatively, an N-channel MOSFET may be used in the same configuration. The current in RB is then reduced compared to the case in which the bipolar transistor is used. For LED currents up to about 400mA a suitable MOSFET is DMN6068SE in the SOT223 package. The design procedure is as follows, referring to Figure 7. Figure 7 Application Circuit Using MOSFET AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 8 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) N-Channel MOSFET as the Pass Element (cont.) The equations (1 and 2) for the bipolar transistor are transformed into: LED circuit path: 5. VCC = (VLED + VDS + VFB) where VFB is approximately the internal reference voltage of 200mV. Control drive circuit path 6. VCC = (VRB + VGS + VFB) The maximum total LED voltage plus the reference voltage determines the minimum supply voltage. Substituting into equation 5 yields: VCC min = VLED + VDSMIN + VFB The MOSFET DC gate current is negligible, so the bias resistor RB has only to provide the minimum output current of the AL8400. So rearranging equation 6 yields the boundaries for allowable RB values: 7. R B min = VCC max − VGS min − VFB IOUT max 8. Where IOUTmax is the AL8400 maximum output current R B max = VCC min − VGS max − VFB IOUT min Where IOUTmin is the AL8400 minimum output current Once the value of RB has been determined, somewhere between RBmax and RBmin – trying to get IOUT close to 1mA for all variations, the value for compensation capacitor, CL, should be calculated. The MOSFET selection is also influenced by the maximum power dissipation PTOT = ILED * (VCC – VLED – VFB) = ILED * VDS Since this determines the package choice (θJA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT • θJA where TJ(MAX) is the maximum operating junction temperature, TA is the ambient temperature, θJA is the junction to ambient thermal resistance. Low Supply Voltages and MOSFET as Pass Element When driving a single LED at low supply voltages, a low threshold MOSFET or high gain NPN bipolar transistor should be used as the LED driving pass transistor. This is because a standard threshold voltage MOSFET might not have enough Gate-Source voltage to ensure that it is sufficiently enhanced to regulate the LED current. MOSFET Example Choosing RB and CL The driver is required to control 3 series connected LEDs at 200mA ±10% from an 12V ±5% supply. Each LED has a forward voltage of 3V minimum and of 3.6V maximum. Therefore the minimum supply voltage is 11.4V and the maximum LED chain voltage is 10.8V. Rearranging equation 5 (page 9); the minimum voltage drop across the MOSFET is required to be: ILED × R DS = VCC min − VLED max − VFB = = 11.4 V − 10.8 V − 0.2V = 0.4V Æ RDS(ON) ≤ 2Ω We will use the DMN6068SE N-channel MOSFET (Q2) with a maximum RDS(ON) of 100mΩ at VGS = 4.5V. AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 9 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) MOSFET Example Choosing RB and CL (cont.) RBmax The minimum recommended IOUT for AL8400 is 0.3mA. The maximum VGS is not stated explicitly, but from the datasheet graphs (Figures 8 and 9) it is expected to be approximately 3.8V at -50°C. RB max = = VCC min − VGS max − VFB = IOUT min 11.4 V − 3.8 V − 0.2V = 24.7kΩ 0.3mA To ensure that the output capability of the AL8400 is not exceeded at maximum VIN and minimum VGS these values should be substituted back into the RB equation to determine the minimum allowable value for RB. RBmin The maximum recommended IOUT for the AL8400 is 15mA. The minimum VGS is about 1V and assuming VCCmax = 8.4V: R B min = = VCC max − VGS min − VFB IOUT max = 12.6 V − 1V − 0.2V 15mA = 480Ω this is less than 12kΩ and so the AL8400 output current is within its ratings. Figure 8 Typical Transfer Characteristics Figure 9 Normalised Curves and Temperature Assuming VGS ~ 3V and choosing an RB = 8.2kΩ satisfies the requirements for the AL8400 conformance and sets approximately 1mA in the OUT pin. The required compensation capacitor can therefore be calculated from: CL ≈ 2ms ≈ 0.243μF Æ 220nF 8.2kΩ The value of RSET is VREF/ILED RSET = 0.2/0.2 = 1Ω Finally, the maximum power dissipation of the external MOSFET is: PTOT = ILED x VDSMAX = ILED x (VCCmax – VLEDMIN – VFB) = 0.2 x( 12.6 – 9 -0.2) = 0.68W This determines the package choice (θJA) in order to keep the junction temperature below the maximum value allowed. TJ = TA + PTOT x θJA = 60 + 0.68 x 62.5 AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 = +102.5˚C 10 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Application Information (cont.) High Voltage Operation The AL8400 also provides the capability to drive longer LED chains as the voltage across the LED chain is determined by the external switch. The lower supply voltage for the AL8400 can be derived from the supply to the LED chain either by putting a series resistor to the AL8400’s VCC pin and putting a suitable zener diode from its VCC to GND Figure 10 or by tapping its VCC from the LED chain Figure 11. Figure 10 High Voltage Operation with Zener Diode from VIN Equations 1 and 2 (from page 7) now transform into: Control Drive Circuit Path LED Circuit Path: 1. VIN = (VLED + VCE + VFB) 2. VCC = (VRB + VBE + VFB) When the supply voltage for the AL8400 is derived using a zener diode, care has to be taken in dimensioning the resistor R1. The current taken through R1 from VIN has to be large enough to polarize the zener, bias the AL8400 supply current, AL8400 output current and the pass transistor across all input voltage variations. An alternative way of operating the AL8400 from rails greater than 18V is to take its power supply from the LED chain itself. Figure 11 High Voltage Operation Tapping VCC from the LED String When the supply voltage for the AL8400 is derived from the LED string, care has to be taken in dimensioning the resistor RB. The current spilled from the LED chain can reduce the accuracy of the system and brightness matching between the LED. AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 11 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Ordering Information Part Number Package Code Packaging AL8400QSE-7 AL8400SE-7 SE SE SOT353 SOT353 Note: 7” Tape and Reel Quantity Part Number Suffix 3000/Tape & Reel -7 3000/Tape & Reel -7 Automotive Grade Y (Note 5) - 5. Qualified to AEC-Q100 Grade 1. Marking Information (1) SOT353 ( Top View ) 4 7 5 XX : Identification code Y : Year 0~9 W : Week : A~Z : 1~26 week; a~z : 27~52 week; z represents 52 and 53 week X : A~Z : Green XX Y W X 1 2 3 Part Number AL8400SE-7 AL8400QSE-7 Package SOT353 SOT353 Identification Code B4 B4 Package Outline Dimensions (All dimensions in mm.) Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version. A SOT353 Dim Min Max A 0.10 0.30 B 1.15 1.35 C 2.00 2.20 D 0.65 Typ F 0.40 0.45 H 1.80 2.20 J 0 0.10 K 0.90 1.00 L 0.25 0.40 M 0.10 0.22 0° 8° α All Dimensions in mm B C H K J M D AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 F L 12 of 13 www.diodes.com August 2012 © Diodes Incorporated AL8400 /AL8400Q Suggested Pad Layout Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. C2 Z C2 Dimensions Value (in mm) Z 2.5 G 1.3 X 0.42 Y 0.6 C1 1.9 C2 0.65 C1 G Y X IMPORTANT NOTICE DIODES INCORPORATED MAKES NO WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, WITH REGARDS TO THIS DOCUMENT, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE (AND THEIR EQUIVALENTS UNDER THE LAWS OF ANY JURISDICTION). Diodes Incorporated and its subsidiaries reserve the right to make modifications, enhancements, improvements, corrections or other changes without further notice to this document and any product described herein. Diodes Incorporated does not assume any liability arising out of the application or use of this document or any product described herein; neither does Diodes Incorporated convey any license under its patent or trademark rights, nor the rights of others. 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Customers represent that they have all necessary expertise in the safety and regulatory ramifications of their life support devices or systems, and acknowledge and agree that they are solely responsible for all legal, regulatory and safety-related requirements concerning their products and any use of Diodes Incorporated products in such safety-critical, life support devices or systems, notwithstanding any devices- or systems-related information or support that may be provided by Diodes Incorporated. Further, Customers must fully indemnify Diodes Incorporated and its representatives against any damages arising out of the use of Diodes Incorporated products in such safety-critical, life support devices or systems. Copyright © 2012, Diodes Incorporated www.diodes.com AL8400/ AL8400Q Document number: DS35115 Rev. 4 - 2 13 of 13 www.diodes.com August 2012 © Diodes Incorporated