AL9902 LINEAR AND PWM DIMMING HIGH VOLTAGE LED DRIVER Description Pin Assignments The AL9902 high-voltage PWM LED driver provides an efficient solution for offline high-brightness LED lamps from rectified line voltages ranging from 85VAC up to 277VAC. The AL9902 has an SW NC SO GND CS VIN 12 11 10 9 8 77 internal MOSFET that allows switching frequencies up to 300kHz, with the switching frequency determined by an external single resistor. The AL9902 topology creates a constant current through the LEDs providing constant light output. The output current is programmed by one external resistor. EP1 The LED brightness can be varied by both linear and PWM dimming using the AL9902’s LD and PWM pins respectively. The PWM input operates with duty ratio of 0-100% and frequency of up to several kHz. 11 2 NC NC EP2 3 4 PWM VDD 5 66 LD Rosc U-DFN6040-12 The AL9902 is available in the thermally enhanced U-DFN6040-12 and SO-16 packages. NC SO NC 16 15 14 1 2 NC NC NC GND CS 13 12 11 10 NC 3 4 5 6 7 SW NC PWM VDD VIN 9 Features >90% Efficiency Universal Rectified 85 to 277VAC Input Range Internal MOSFET Up to 650V, 2A High Switching Frequency Up to 300kHz Internal Voltage Regulator Removes Start-Up Resistor 7.5V Regulated Output Tighter Current Sense Tolerance Better Than ±5% LED Brightness Control with Linear and PWM Dimming Internal Over-Temperature Protection (OTP) U-DFN6040-12 and SO-16 Packages Totally Lead-Free & Fully RoHS compliant (Notes 1 & 2) Halogen and Antimony Free. “Green” Device (Note 3) Notes: LD 8 Rosc SO-16 Applications LED Offline Lamps High Voltage DC-DC LED Driver Signage and Decorative LED Lighting Back Lighting of Flat Panel Displays General Purpose Constant Current Source 1. No purposely added lead. Fully EU Directive 2002/95/EC (RoHS) & 2011/65/EU (RoHS 2) compliant. 2. See http://www.diodes.com/quality/lead_free.html 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 1 AC+ AC- Z1 602V 2 HD06 3 C1 C3 4 D1 VIN VDD LD AL9902 PWM GND C2 AL9902 Document number: DS37878 Rev. 1 - 2 Rosc SW SO CS L1 Rosc Rsense 1 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Pin Descriptions Pin Name NC NC PWM U-DFN5040-10 1 2 3 SO-16 Functions 14 No connection 1, 2, 4, 10,16 No connection 5 Low Frequency PWM Dimming pin, also Enable input. Internal 200kΩ pull-down to GND Internally regulated supply voltage. 7.5V nominal. 6 Can supply up to 1 mA for external circuitry. A sufficient storage capacitor is used to provide storage when the rectified AC input is near the zero crossing. Linear Dimming input. Changes the current limit threshold at current sense comparator and changes the average LED current. 7 VDD 4 LD 5 ROSC 6 8 VIN CS GND NC SO SW EP1 7 9 8 9 11 10 12 EP1 EP2 EP2 11 12 13 15 3 NA NA Oscillator control. A resistor connected between this pin and ground puts the AL9902 into fixed frequency mode and sets the switching frequency. Input voltage Senses LED string and internal MOSFET switch current Device ground No connection Source of the internal MOSFET Switch Drain of the internal MOSFET switch. Exposed Pad 1(bottom). Drain connection of internal power MOSFET. Exposed Pad 2 (bottom). Substrate connection of control IC. Connect to GND directly underneath the package and large PCB area to minimize junction to ambient thermal impedance. Functional Block Diagram & Typical Application VIN VIN VDD LDO OSC 7.5V D1 Rosc VDD 250mV S SW Rosc R LD SO CS OTP PWM Rsense 200K AL9902 GND AL9902 Document number: DS37878 Rev. 1 - 2 2 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Absolute Maximum Ratings (Note 4) (@TA = +25°C, unless otherwise specified.) Symbol Ratings Unit Maximum Input Voltage, VIN, to GND -0.5 to +520 V VCS Maximum CS Input Pin voltage Relative to GND -0.3 to +0.45 V VLD Maximum LD Input Pin Voltage Relative to GND -0.3 to (VDD +0.3) V Maximum PWM input Pin Voltage Relative to GND -0.3 to (VDD +0.3) V -0.5 to +650 V VIN(MAX) VPWM Parameter VSW Maximum MOSFET Drain Pin Voltage Relative to GND VSO Maximum MOSFET Source Pin Voltage Relative to GND -0.5 to (VDD +0.3) V VGate Maximum MOSFET GATE pin Voltage Relative to GND -0.5 to (VDD +0.3) V 8.1 V VDD(MAX) Maximum VDD Pin Voltage Relative to GND - Continuous Power Dissipation (TA = +25C) - U-DFN6040-12 (derate 10mW/C above +25C) - - 1,000 mW TJ Junction Temperature Range +150 °C TST ESD HBM Storage Temperature Range -65 to +150 °C 2,000 V Notes: Human Body Model ESD Protection (Note 5) 4. Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those listed in the operational sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. All voltages are with respect to Ground. Currents are positive into, negative out of the specified terminal. 5. Semiconductor devices are ESD sensitive and may be damaged by exposure to ESD events. Suitable ESD precautions should be taken when handling and transporting these devices. Maximum Ratings of Internal MOSFET (@TA = +25°C, unless otherwise specified.) Characteristic Drain-Source Voltage Gate-Source Voltage Continuous Drain Current (Note 5) VGS = 10V Steady State TC = +25°C TC = +100°C Symbol Value Units VDSS 650 V VGSS ±30 V ID 1.6 1 A A Pulsed Drain Current (Note 6) IDM 3 Avalanche Current (Note 7) VDD = 100V, VGS = 10V, L = 60mH IAR 0.8 A Repetitive Avalanche Energy (Note 7) VDD = 100V, VGS = 10V, L = 60mH EAR 22 mJ Peak Diode Recovery dv/dt 5 V/ns Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Symbol Min Max Input DC Supply Voltage Range 20 500 V TA Ambient Temperature Range -40 +105 °C ISW Switch Pin Output Current - 0.4 A VDD Maximum Recommended Voltage Applied to VDD Pin (Note 6) - 8.1 V VINDC Parameter VPWM(lo) Pin PWM input Low Voltage 0 1 VPWM(hi) Pin PWM input High Voltage 2.4 VDD Note: Unit V 6. when using the AL9902 in isolated LED lamps an auxiliary winding might be used. AL9902 Document number: DS37878 Rev. 1 - 2 3 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Electrical Characteristics (@TA = +25°C, unless otherwise specified.) Specifications apply to AL9902 unless otherwise specified Symbol Parameter Ishdn Shut-Down Mode Supply Current VDD Internally Regulated Voltage IDD(ext) Conditions Pin PWM to GND, VIN = 20V VIN = VIN(MIN) ~ 500V, (Note 8) lDD(ext) = 0, Gate pin open Min Typ Max Unit - 0.5 1 mA 7.2 7.5 8.1 V - - 1.0 mA 6.4 6.7 7.2 V VDD Current Available for External Circuitry VIN = 20 to 100V (Note 7) UVLO VDD Under Voltage Lockout Threshold VDD rising ∆UVLO VDD Under Voltage Lockout Hysteresis VDD falling - 500 - mV RPWM PWM Pull-Down Resistance VPWM= 5V 150 200 250 kΩ VT MOSFET Threshold Voltage ISW = 0.5A - 4 - V VFD MOSFET Diodes Forward Voltage ID = 0.5A - 0.85 - V Current Sense Threshold Voltage TA = -40°C to +125°C mV VCS(hi) Oscillator Frequency fOSC 237.5 250 262.5 ROSC = 1MΩ 20 25 30 ROSC = 226kΩ 80 100 120 kHz DMAXhf Maximum Oscillator PWM Duty Cycle fPWMhf = 25kHz, at GATE, CS to GND. - - 100 % VLD Linear Dimming Pin Voltage Range TA = <125°C, VIN = 20V 0 - 250 mV TSD Thermal Shut-Down (Junction) Use DFN JA when ISW=0.4A, VDS=1V - 141 - TSDH Thermal Shut-Down Hysteresis - - 25 - - 65 - C/W - 5 - C/W - 100 - C/W - 15 - C/W JA Thermal Resistance Junction-to-Ambient JC Thermal Resistance Junction-to-Case JA Thermal Resistance Junction-to-Ambient JC Thermal Resistance Junction-to-Case Notes: U-DFN6040-12 (Note 8) SO-16 °C 7. Also limited by package power dissipation limit, whichever is lower. 8. Device mounted on FR-4 PCB (25mm x 25mm 1oz copper, minimum recommended pad layout on top. For better thermal performance, larger copper pad for heat-sink is needed. Internal MOSFET Characteristic OFF CHARACTERISTICS (Note 9) Symbol Min Typ Max Unit Test Condition Drain-Source Breakdown Voltage BVDSS 650 — — V VGS = 0V, ID = 250μA Zero Gate Voltage Drain Current IDSS — — 1 µA VDS = 650V, VGS = 0V Gate-Source Leakage IGSS — — ±100 nA VGS = ±30V, VDS = 0V VGS(th) 3 — 5 V VDS = VGS, ID = 250μA RDS (ON) — 4 5 Ω VGS = 10V, ID = 1A VSD — 0.7 1 V VGS = 0V, IS = 1A Ciss — 479 — pF Output Capacitance Coss — 29 — pF Reverse Transfer Capacitance Crss — pF Rg — 1.9 2 — Gate Resistance — Ω Total Gate Charge Qg — 14 — nC Gate-Source Charge Qgs — 2.5 — nC Gate-Drain Charge Qgd — 7.3 — nC Turn-On Delay Time tD(on) — 17 — ns Turn-On Rise Time tr — 33 — ns Turn-Off Delay Time tD(off) — 31 — ns Turn-Off Fall Time tf — 25 — ns Body Diode Reverse Recovery Time trr — 174 — ns Qrr — 884 — nC ON CHARACTERISTICS (Note 9) Gate Threshold Voltage Static Drain-Source On-Resistance Diode Forward Voltage DYNAMIC CHARACTERISTICS (Note 10) Input Capacitance Body Diode Reverse Recovery Charge Notes: VDS = 25V, VGS = 0V, f = 1MHz VDS = 0V, VGS = 0V, f = 1MHz VDS = 520V, VGS = 10V, ID = 2A VDS = 325V, VGS = 10V, RG = 25Ω, ID = 2.5A VDS = 100V, IF = 2A, di/dt = 100A/μs 9. Short duration pulse test used to minimize self-heating effect. 10. Guaranteed by design. Not subject to production testing. AL9902 Document number: DS37878 Rev. 1 - 2 4 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 3.0 460 2.5 440 2.0 420 INPUT CURRENT (µA) CURRENT SENSE THRESHOLD (mV) Typical Characteristics 1.5 1.0 0.5 0.0 V IN = 15V 380 360 340 300 -1.0 280 -40 -1.5 -40 -15 10 35 60 85 AMBIENT TEMPERATURE (°C) Change in Current Sense Threshold vs. Ambient Temperature -15 10 35 60 AMBIENT TEMPERATURE (°C) 85 Input Current vs. Ambient Temperature 450 1.0 0.5 ROSC = 226k -0.5 R OSC = 1M -1.0 -1.5 -2.0 -40 -15 10 35 60 85 AMBIENT TEMPERATURE (°C) Change in Oscillation Frequency vs. Ambient Temperature SHORT CIRCUIT OUTPUT CURRENT (mA) 1.5 CHANGE IN FREQUENCY (%) 400 320 -0.5 0.0 V IN = 400V ILED(NOM) = 180mA 400 350 300 250 200 150 85 105 125 145 165 185 205 225 245 265 INPUT VOLTAGE (VRMS) 180mA LED Driver Short Circuit Output Current vs. Input Voltage IOUT vs. VLD Dimming Control AL9902 Document number: DS37878 Rev. 1 - 2 IOUT vs. PWM Dimming Control at 1KHz 5 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Typical Characteristics (continued) 180mA LED Driver Output Current vs. Input Voltage 180mA LED Driver Power Factor vs. Input Voltage AL9902 Document number: DS37878 Rev. 1 - 2 180mA LED Driver Efficiency vs. Input Voltage 180mA LED Driver Input Power Dissipation vs. Input Voltage 6 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Typical Characteristics (cont.) 2.0 1.8 VDS = 20V VGS = 10V VGS = 6.0V ID, DRAIN CURRENT (A) VGS = 8.0V 1.6 ID, DRAIN CURRENT (A) 10 VGS = 20V 1.4 1.2 1.0 VGS = 5.5V 0.8 0.6 1 0.1 TA = 150°C 0.01 0.4 TA = 85°C 0.2 TA = -55°C VGS = 5.0V 0 1 2 3 4 5 6 7 8 9 VDS, DRAIN-SOURCE VOLTAGE (V) Figure 1 Typical Characteristics Typical Output Output Characteristics 10 0.001 4.8 4.6 4.4 4.2 VGS = 10V 4 3.8 3.6 3.4 3.2 3 0 1 2 3 4 5 6 7 VGS, GATE-SOURCE VOLTAGE (V) Typical Transfer Characteristics Figure 2 Typical Transfer Characteristics 8 20 5 R DS(ON), DRAIN-SOURCE ON-RESISTANCE () RDS(ON), DRAIN-SOURCE ON-RESISTANCE () 0.0 TA = 25°C TA = 125°C 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 ID, DRAIN-SOURCE CURRENT (A) Figure 3 Typical On-Resistance vs. Drain vs. Current Gateand Voltage Typical On-Resistance Drainand Current Gate Voltage AL9902 Document number: DS37878 Rev. 1 - 2 7 of 18 www.diodes.com 18 16 14 ID = 1.0A 12 10 8 6 4 2 0 4 6 8 10 12 14 16 18 20 VGS, GATE-SOURCE VOLTAGE (V) Figure 4 Typical Transfer Characteristics Typical Transfer Characteristics July 2015 © Diodes Incorporated AL9902 3 15 VGS = 10V 12 RDS(ON), DRAIN-SOURCE ON-RESISTANCE (NORMALIZED) RDS(ON), DRAIN-SOURCE ON-RESISTANCE () Typical Characteristics (cont.) Internal MOSFET TA = 150°C TA = 125°C 9 TA = 85°C 6 TA = 25°C 3 TA = -55°C 0 2 VGS = 10 V ID = 1A 1.5 1 0.5 0 -50 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 ID, DRAIN CURRENT (A) Typical On-Resistance DrainOn-Resistance Current and Temperature Figure 5vs. Typical vs. Drain Current and Temperature 0 -25 0 25 50 75 100 125 150 TJ, JUNCTION TEMPERATURE ( C) On-Resistance Variation withwith Temperature Figure 6 On-Resistance Variation Temperature 15 5 VGS(th), GATE THRESHOLD VOLTAGE (V) RDS(ON), DRAIN-SOURCE ON-RESISTANCE () VGS = 20V ID = 2A 2.5 12 VGS = 20V ID = 2A 9 VGS = 10V ID = 1A 6 3 0 -50 AL9902 Document number: DS37878 Rev. 1 - 2 ID = 250µA ID = 1mA 4 3.5 3 2.5 2 -25 0 25 50 75 100 125 150 TJ, JUNCTION TEMPERATURE (C) Figure 7 On-Resistance Variation with Temperature On-Resistance Variation with Temperature 4.5 -50 -25 0 25 50 75 100 125 150 TJ, JUNCTION TEMPERATURE ( C) Figure 8 Gate Threshold Variation vs. Ambient Temperature Gate Threshold Variation vs. Ambient Temperature 8 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Typical Characteristics (cont.) Internal MOSFET 2 1000 Ciss CT, JUNCTION CAPACITANCE (pF) 1.8 IS, SOURCE CURRENT (A) 1.6 1.4 TA = 150°C 1.2 T A = 25°C 1 TA = 125°C 0.8 TA = -55°C 0.6 TA = 85°C 0.4 100 Coss 10 Crss 0.2 f = 1MHz 0 0 1 0.3 0.6 0.9 1.2 1.5 V SD, SOURCE-DRAIN VOLTAGE (V) Figure Diode Forward vs. Current Diode9Forward VoltageVoltage vs. Current 0 5 10 15 20 25 30 35 VDS, DRAIN-SOURCE VOLTAGE (V) Typical10Typical Junction Junction Capacitance Figure Capacitance 40 10 10 8 ID, DRAIN CURRENT (A) VGS GATE THRESHOLD VOLTAGE (V) RDS(on) Limited 6 VDS = 520V ID = 2A 4 1 DC PW = 1s PW = 100ms PW = 10ms 0.01 2 0 0 2 4 6 8 10 12 14 Qg, TOTAL GATE CHARGE (nC) Figure 11 Gate Charge Gate Charge AL9902 Document number: DS37878 Rev. 1 - 2 16 PW = 10s 0.1 0.001 1 TJ(max) = 150°C TA = 25°C VGS = 10V Single Pulse DUT on 1 * MRP Board PW = 1ms PW = 100µs 10 100 VDS, DRAIN-SOURCE VOLTAGE (V) Figure 12 SOA, Safe Operation Area SOA, Safe Operation Area 9 of 18 www.diodes.com 1000 July 2015 © Diodes Incorporated AL9902 Applications Information DC-DC and Offline LED Driver The AL9902 is a cost-effective offline buck LED driver-converter specifically designed for driving LED strings. It is suitable for being used with either rectified AC line or any DC voltage between 5-500V. See Figure 1 for typical circuit. 1 AC+ 2 Z1 602V AC- HD06 3 C1 C3 4 D1 VIN VDD LD AL9902 PWM GND C2 Rosc SW SO CS L1 Rosc Rsense Figure 1 Typical Application Circuit (without PFC) Buck Design Equations: D VLEDs VIN t ON L D f osc ( VIN VLEDs ) t ON 0.3 ILED RSENSE 0.25 Where ILED x 0.3 = IRIPPLE ILED (0.5 (ILED 0.3)) Design Example For an AC line voltage of 120V, the nominal rectified input voltage VIN = 120V x 1.41 = 169V. From this and the LED chain voltage the duty cycle can be determined: D = VLEDs /VIN = 30/169 = 0.177 From the switching frequency, for example fOSC = 50 kHz, the required on-time of the internal MOSFET can be calculated: tON = D/fOSC = 3.5 µs The value of the inductor is determined as follows: L = (VIN - VLEDs) * tON / (0.3 * ILED) = 4.6mH AL9902 Document number: DS37878 Rev. 1 - 2 10 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Applications Information (continued) Input Bulk Capacitor For offline lamps, an input bulk capacitor is required to ensure that the rectified AC voltage is held above twice the LED string voltage throughout the AC line cycle. The value can be calculated from: CIN Pin (1 Dch ) 2 VLine _ min 2fL VDC _ max Where Dch : Capacity charge work period, generally about 0.2~0.25 fL : Input frequency for full range (85~265VRMS) VDC _ max Should be set 10~15% of 2 VLine _ min If the capacitor has a 15% voltage ripple then a simplified formula for the minimum value of the bulk input capacitor approximates to: I VLEDs 0.06 CMIN = LED VIN2 Power Factor Correction If power factor improvement is required then for the input power less than 25W, a simple method for improving the power factor can be implemented by potential dividing down the rectified mains voltage (resistors R1 and R2 in Figure 2) and feeding it into the LD pin. The current drawn from the supply voltage will follow an approximate half sine wave. A filter across the LEDs reduces the potential for flicker. This circuit also significantly reduces the size of input capacitors. L1 1 AC+ Z1 602V 2 LED+ HD06 AC- C1 4 R2 C4 C2 D4 LD VDD R1 VIN AL9902 PWM GND C3 Rosc LED- SW SO CS L2 Rosc Rsense Figure 2 Typical Application Circuit with Simple PFC Passive power factor correction using 3 high voltage diodes and 2 identical capacitors can be implemented. For further design information please see AN75 from the Diodes website. DC-DC Buck LED Driver The design procedure for an AC input buck LED driver outlined in the previous chapters equally applies to DC input LED drivers. AL9902 Document number: DS37878 Rev. 1 - 2 11 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Applications Information (cont.) DC-DC Boost LED Driver Due to the topology of the AL9902 LED driver-converter, it is capable of being used in boost configurations as shown in Figure 3 – at reduced accuracy. The accuracy can be improved by measuring the LED current with an op amp and use the op amp’s output to drive the LD pin. A Boost LED driver is used when the forward voltage drop of the LED string is higher than the input supply voltage. For example, the Boost topology can be appropriate when input voltage is supplied by a 48V power supply and the LED string consists of twenty HB LEDs, as the case may be for a street light. L1 VIN VDD VIN PWM C1 AL9902 LD GND C2 Rosc SW SO CS D1 Rosc C3 Rsense Figure 3 Boost LED driver In a Boost converter, when the internal MOSFET is ON, the energy is stored in the inductor which is then delivered to the output when the internal MOSFET switches OFF. If the energy stored in the inductor is not fully depleted by the next switching cycle (continuous conduction mode) the DC conversion between input and output voltage is given by: VOUT VIN V VIN , D OUT 1 D VOUT From the switching frequency, fOSC, the on-time of the MOSFET can be calculated: t ON D fOSC From this the required inductor value can be determined by: L VIN t ON 0.3 ILED The Boost topology LED driver requires an output capacitor to deliver current to the LED string during the time that the internal MOSFET is on. In boost LED driver topologies, if the LEDs should become open circuit damage may occur to the power switch and so some form of detection should be present to provide overvoltage detection/protection. AL9902 Document number: DS37878 Rev. 1 - 2 12 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Applications Information (cont.) General Application The AL9902 is capable of operating in isolated or non-isolated topologies. It can also be made to operate in continuous as well as discontinuous conduction mode. VIN VIN VDD LDO OSC 7.5V D1 Rosc VDD 250mV S SW Rosc R LD SO CS OTP Rsense PWM 200K AL9902 GND Figure 4 Typical Application Circuit The AL9902 contains a high-voltage LDO (see figure 4), the output of the LDO provides a power rail to the internal circuitry including the gate driver. A UVLO on the output of the LDO prevents incorrect operation at low input voltage to the VIN pin. In a non-isolated Buck LED driver when the gate pin goes high, the internal power MOSFET (Q1) is turned on causing current to flow through the LEDs, inductor (L1) and current sense resistor (RSENSE). When the voltage across RSENSE exceeds the current sense pin threshold, the internal MOSFET Q1 is turned off. The energy stored in the inductor causes the current to continue to flow through the LEDs via diode D1. The AL9902’s LDO provides all power to the rest of the IC including gate drive and this removes the need for large high power start-up resistors. This means that to during normal operation the AL9902 requires around 0.5mA from the high voltage power rail. The LDO can also be used to supply up to 1mA to external circuits. The AL9902 operates and regulates by limiting the peak current of the internal MOSFET; the peak current sense threshold is nominally set at 250mV. The AL9902 is capable of operating in a fixed frequency (PWM) mode and also variable frequency (fixed off-time) mode to regulate the LED current. The same basic operation is true for isolated topologies; however in these the energy stored in the transformer delivers energy to LEDs during the off-cycle of the internal MOSFET. The on-resistance of the AL9902’s internal power MOSFET means that it can drive up to 2A. Design Parameters Setting the LED Current In the non-isolated buck converter topology, figure 4, the average LED current is not the peak current divided by 2 - however, there is a certain error due to the difference between the peak and the average current in the inductor. The following equation accounts for this error: R SENSE 250mV ILED (0.5 * IRIPPLE )) AL9902 Document number: DS37878 Rev. 1 - 2 . 13 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Applications Information (cont.) Setting Operating Frequency The AL9902 is capable of operating between 25 and 450kHz switching frequency range. The switching frequency is programmed by connecting an external resistor between ROSC pin and ground. The corresponding oscillator period is: tOSC = R osc 22 µs 25 with ROSC in kΩ The switching frequency is the reciprocal of the oscillator period. Typical values for R OSC vary from 75kΩ to 1MΩ. In buck mode the duty cycle, D, is VLEDs ; so when driving small numbers of LEDs from high-input voltages, the duty cycle will be reduced and VIN care should be taken to ensure that tON > tBLANK. The simplest way to do this is to reduce/limit the switching frequency by increasing the R OSC value. Reducing the switching frequency will also improve the efficiency. When operating in buck mode, the designer must keep in mind that the input voltage must be maintained higher than two times the forward voltage drop across the LEDs. This limitation is related to the output current instability that may develop when the AL9902 operates at a duty cycle greater than 0.5. This instability reveals itself as an oscillation of the output current at a sub-harmonic (SBO) of the switching frequency. Inductor Selection The non-isolated buck circuit, Figure 4, is usually selected and has two operation modes: continuous and discontinuous conduction modes. A buck power stage can be designed to operate in continuous mode for load current above a certain level usually 15% to 30% of full load. Usually the input voltage range, the output voltage and load current are defined by the power stage specification. This leaves the inductor value as the only design parameter to maintain continuous conduction mode. The minimum value of inductor to maintain continuous conduction mode can be determined by the following example. The required inductor value is determined from the desired peak-to-peak LED ripple current in the inductor; typically around 30% of the nominal LED current. L= VIN VLEDs D 0.3 ILED fOSC , where D is duty cycle The next step is determining the total voltage drop across the LED string. For example, when the string consists of 10 High-Brightness LEDs and each diode has a forward voltage drop of 3.0V at its nominal current; the total LED voltage V LEDS is 30V. Dimming The LED brightness can be dimmed either linearly (using the LD pin) or via pulse width modulation (using the PWM-D pin); or a combination of both - depending on the application. Pulling the PWM pin to ground will turn off the AL9902. When disabled, the AL9902’s quiescent current is typically 0.5mA. Reducing the LD voltage will reduce the LED current but it will not entirely turn off the external power transistor and hence the LED current – this is due to the finite blanking period. Only the PWM pin will turn off the power transistor. Linear dimming is accomplished by applying a 45 to 250mV analog signal to the LD pin. This overrides the default 250mV threshold level of the CS pin and reduces the output current. If an input voltage greater than 250mV is applied to the LD then the output current will not change. The LD pin also provides a simple cost-effective solution to soft start; by connecting a capacitor to the LD pin down to ground at initial power up, the LD pin will be held low causing the sense threshold to be low. As the capacitor charges up the current sense threshold will increase thereby causing the average LED current to increase. PWM dimming is achieved by applying an external PWM signal to the PWM pin. The LED current is proportional to the PWM duty cycle and the light output can be adjusted between 0 and 100%. The PWM signal enables and disables the AL9902 - modulating the LED current. The ultimate accuracy of the PWM dimming method is limited only by the minimum gate pulse width, which is a fraction of a percentage of the low frequency duty cycle. PWM dimming of the LED light can be achieved by turning on and off the converter with low frequency 50Hz to 1000Hz TTL logic level signal. With both modes of dimming it is not possible to achieve average brightness levels higher than the one set by the current sense threshold level of the AL9902. If a greater LED current is required then a smaller sense resistor should be used. Output Open Circuit Protection The non-isolated buck LED driver topology provides inherent protection against an open circuit condition in the LED string due to the LEDs being connected in series with the inductor. Should the LED string become open circuit then no switching occurs and the circuit can be permanently left in this state with damage to the rest of the circuit. AL9902 Document number: DS37878 Rev. 1 - 2 14 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Ordering Information AL9902 XXX - 13 Package Packing FDF : U-DFN6040-12 S16 : SO-16 13 : Tape & Reel Part Number VCS Tolerance Package Code Packaging AL9902FDF-13 AL9902S16-13 ±5% ±5% FDF S16 U-DFN6040-12 SO-16 13” Tape and Reel Quantity Part Number Suffix 3,000/Tape & Reel -13 3,000/Tape & Reel -13 Marking Information ( Top View ) Logo Part Number AL9902 Document number: DS37878 Rev. 1 - 2 AL9902 YY WW X X YY : Year : 15, 16,17~ WW : Week : 01~52; 52 represents 52 and 53 week X X : Internal Code 15 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Package Outline Dimensions (All dimensions in mm.) Please see AP02002 at http://www.diodes.com/datasheets/ap02002.pdf for latest version. U-DFN6040-12 A1 A3 A U-DFN6040-12 Dim Min Max Typ A 0.55 0.65 0.60 A1 0 0.05 0.02 A3 0.15 b 0.35 0.45 0.40 D 5.95 6.05 6.00 D1 1.95 2.15 2.05 D2 2.35 2.55 2.45 e 1.00 E 3.95 4.05 4.00 E1 2.10 2.30 2.20 E2 1.80 2.00 1.90 L 0.35 0.45 0.40 Z 0.30 All Dimensions in mm Seating Plane D e D2 D1 E E2 E1 L b Z SO-16 H E Gauge Plane L Detail ‘A’ D A A2 B AL9902 Document number: DS37878 Rev. 1 - 2 e A1 C SO-16 Dim Min Max A 1.40 1.75 A1 0.10 0.25 A2 1.30 1.50 B 0.33 0.51 C 0.19 0.25 D 9.80 10.00 E 3.80 4.00 e 1.27 Typ H 5.80 6.20 L 0.38 1.27 0 8 All Dimensions in mm Detail ‘A’ 16 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 Suggested Pad Layout Please see AP02001 at http://www.diodes.com/datasheets/ap02001.pdf for the latest version. U-DFN6040-12 X3 Dimensions Y C G Y1 X1 G1 X2 Y2 Y3 Pin1 C G G1 X X1 X2 X3 Y Y1 Y2 Y3 Value (in mm) 0.500 0.650 0.350 0.250 1.075 1.275 2.750 0.400 1.150 1.000 2.300 X SO-16 X1 Dimensions C X X1 Y Y1 Y1 Y Value (in mm) 1.270 0.670 9.560 1.450 6.400 Pin 1 X AL9902 Document number: DS37878 Rev. 1 - 2 C 17 of 18 www.diodes.com July 2015 © Diodes Incorporated AL9902 IMPORTANT NOTICE DIODE 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. Any Customer or user of this document or products described herein in such applications shall assume all risks of such use and will agree to hold Diodes Incorporated and all the companies whose products are represented on Diodes Incorporated website, harmless against all damages. Diodes Incorporated does not warrant or accept any liability whatsoever in respect of any products purchased through unauthorized sales channel. Should Customers purchase or use Diodes Incorporated products for any unintended or unauthorized application, Customers shall indemnify and hold Diodes Incorporated and its representatives harmless against all claims, damages, expenses, and attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized application. Products described herein may be covered by one or more United States, international or foreign patents pending. Product names and markings noted herein may also be covered by one or more United States, international or foreign trademarks. This document is written in English but may be translated into multiple languages for reference. Only the English version of this document is the final and determinative format released by Diodes Incorporated. LIFE SUPPORT Diodes Incorporated products are specifically not authorized for use as critical components in life support devices or systems without the express written approval of the Chief Executive Officer of Diodes Incorporated. As used herein: A. Life support devices or systems are devices or systems which: 1. are intended to implant into the body, or 2. support or sustain life and whose failure to perform when properly used in accordance with instructions for use provided in the labeling can be reasonably expected to result in significant injury to the user. B. A critical component is any component in a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or to affect its safety or effectiveness. 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 © 2015, Diodes Incorporated www.diodes.com AL9902 Document number: DS37878 Rev. 1 - 2 18 of 18 www.diodes.com July 2015 © Diodes Incorporated