EVALUATION KIT AVAILABLE MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps General Description Benefits and Features The IC can be used in buck, boost, and buck-boost topologies and features. It has an integrated 0.2I (max), 48V switching MOSFET. ●● Minimal Component Count Saves Cost and Space • Integrated 0.2Ω (max) 48V Switching MOSFET The MAX16840 is an LED driver IC for lighting applications. It includes all the necessary features to design lowcomponent-count LED drivers for 12V AC and 24V AC input (e.g., MR16) light bulbs. A proprietary input-current control scheme allows LED lamps based on this device to be compatible with electronic transformers, and dimmable with standard trailing-edge dimmers (where electronic transformers are present). The IC uses constant-frequency average current-mode control. It senses the input current through the voltage at the FB pin, and regulates its average. An input pin (REFI) allows the setting of the input-current level. When the voltage at this pin is set below a certain threshold, the input current is proportional to this voltage, while when that voltage is beyond the threshold, the input current is set at a fixed, predefined level. This nonlinear behavior of REFI allows its use to achieve thermal foldback, by connecting it to an NTC resistor. The IC also features an internal overvoltage protection on the IN pin to protect the internal switching MOSFET from damage if the LED string is open or if the voltage on the LED string is too high. The IC has a separate EXT pin that can be used to guarantee that there is a kick-start of current at turn-on for lowinput voltages for proper operation with electronic transformers. EXT drives an external npn transistor. Once the UVLO threshold of 5.5V is crossed on IN, EXT is pulled to ground and the external npn transistor is turned off. The IC is available in a 3mm x 3mm, 10-pin TDFN power package, and is rated over the -40NC to +125NC operating temperature range. Applications MR16 and Other 12V AC or DC Input LED Lighting Applications ●● Cost-Effective Solution for MR16 and Other SSL Applications • Proprietary Input Current-Control Scheme to Achieve Electronic Transformer Compatibility and Dimmability • Buck, Boost, SEPIC, and Buck-Boost Topologies • Analog Dimming ●● Protection Features and Wide Operating Temperature Range Improves Reliability • Thermal-Foldback Protection • Output Overvoltage Protection • Internal Overtemperature Protection • Available in a 10-Pin Thermally Enhanced TDFN Package • Operation Over -40°C to +125°C Temperature Range Ordering Information PART TEMP RANGE PIN-PACKAGE MAX16840ATB+ -40NC to +125NC 10 TDFN-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Typical Operating Circuit LEDL2 R3 L1 12V AC C2 DRAIN BD1 IN REFI EXT C1 MAX16840 COMP C4 R2 19-5671; Rev 4; 1/15 D1 SOURCE FB GND R1 LED+ MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Absolute Maximum Ratings IN, DRAIN to GND..................................................... -0.3V, +52V EXT, COMP, REFI to GND........................................ -0.3V, +6.0V FB, SOURCE to GND............................................... -0.3V, +1.5V Maximum RMS Current, FB, SOURCE to GND.....................0.8A Maximum RMS Current Through DRAIN and SOURCE....... Q2A Continuous Power Dissipation (TA = +70NC) TDFN (derate 24.4mW/NC above +70NC)...................1951mW Any Pin to Any Pin ESD Rating................................ ±2kV (HBM) Operating Temperature Range......................... -40NC to +125NC Maximum Junction Temperature......................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Package Thermal Characteristics (Note 1) TDFN Junction-to-Ambient Thermal Resistance (BJA).......... 41NC/W Junction-to-Case Thermal Resistance (BJC)................. 9NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Electrical Characteristics (VIN = 12V; VEXT = VSOURCE = VFB = VGND = 0V; COMP, REFI, and DRAIN = open; TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER Operating Voltage Range SYMBOL VIN CONDITIONS MIN When MOSFET fully on IN Supply Current Undervoltage Lockout IIN UVLOIN UVLO Hysteresis Overvoltage Protection on IN When MOSFET switching, VCOMP = 2V, drain to 5V through 50I IN rising 5 VOVP IN rising 43.6 270 Ramp P-P Voltage FB Average Voltage COMP Sink Current COMP Source Current Power Switch On-Resistance Switch Leakage Current UNITS 48 V 1 2 1.5 3 5.6 6.1 46 gm A ISINK ISOURCE RDSON ILEAK 300 48 196 -40°C P TA P +125NC 190 200 V V V 330 2 TA = +25NC mA mV 1.2 Switching Frequency No-Load Gain MAX 200 OVP Hysteresis Transconductance TYP 6.5 kHz V 204 210 mV 550 FS 75 dB VCOMP = 2V, VFB = 0.65V 150 250 350 FA VCOMP = 2V, VFB = 0V IDS = 1A 70 115 160 FA 0.1 0.2 I 25 FA VDRAIN = 48V, VCOMP = 0V DRAIN Rise Time tRDRAIN IDS = 1A 10 ns DRAIN Fall Time tFDRAIN IDS = 1A 10 ns SOURCE Limit Threshold www.maximintegrated.com VSOURCETH SOURCE connected to FB 0.66 0.72 0.78 V Maxim Integrated │ 2 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Electrical Characteristics (continued) (VIN = 12V; VEXT = VSOURCE = VFB = VGND = 0V; COMP, REFI, and DRAIN = open; TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN SOURCE Current-Limit Comparator Propagation Delay FB Input Bias Current MAX 25 IFB VFB = 0V and VFB = 0.3V -1 FB Current-Limit Comparator Leading-Edge Blanking REFI Source Current VREFI = 1.224V 47.5 Foldback Kick in Threshold Falling on REFI VREFI = 1.15V FB Average Voltage During Foldback TYP UNITS ns +1 50 FA ns 50 52.5 FA 1.135 1.2 1.255 V 178 189 201 VREFI = 1V 153 164.5 176 VREFI = 0.8V 120 132 143 FB Average Voltage to REFI Gain VREFI = 1V EXT Drive Current VIN = 2V, VEXT = 1V EXT Pulldown Resistance mV 6.075 12.5 40 5 10 mA 20 kI Thermal-Shutdown Temperature Temperature rising 165 NC Thermal Shutdown Hysteresis 15 NC Note 2: All devices are 100% tested at TA = TJ = +25NC. Limits over temperature are guaranteed by design. www.maximintegrated.com Maxim Integrated │ 3 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) 1.2 1.5 180 IQ (mA) 1.0 IQ (mA) VFB (mV) MAX16840 toc03 1.4 190 2.0 MAX16840 toc02 1.6 MAX16840 toc01 200 IQ vs. VIN IQ vs. TEMPERATURE VFB vs. DUTY CYCLE FOR BUCK-BOOST 210 0.8 1.0 0.6 170 0.5 0.4 160 0.2 0 150 30 40 50 60 70 80 90 100 10 35 60 85 0 110 5 VIN (V) OSCILLATOR FREQUENCY vs. TEMPERATURE ULVOIN vs. TEMPERATURE 5.7 VIN RISING AND FALLING 250 200 150 100 MAX16840 toc05 5.8 MAX16840 toc04 300 fSW (kHz) 10 15 20 25 30 35 40 45 50 TEMPERATURE (°C) DUTY CYCLE (%) 50 5.6 5.5 5.4 5.3 5.2 VIN RISING 5.1 VIN FALLING 5.0 0 10 35 60 85 10 110 35 60 85 110 TEMPERATURE (°C) TEMPERATURE (°C) VFB vs. TEMPERATURECOMPATIBILITY MODE VFB vs. VREFI 195 190 MAX16840 toc07 250 MAX16840 toc06 200 200 180 VFB (mV) VFB (mV) 185 175 170 150 100 165 160 50 155 150 10 35 60 85 TEMPERATURE (°C) www.maximintegrated.com 110 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 VREFI (V) Maxim Integrated │ 4 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Pin Configuration TOP VIEW DRAIN 1 DRAIN 2 IN 3 EXT 4 COMP 5 + MAX16840 EP 10 SOURCE 9 SOURCE 8 FB 7 GND 6 REFI TDFN Pin Description PIN NAME 1, 2 DRAIN 3 IN 4 EXT 5 COMP FUNCTION Drain of the Internal Switching MOSFET Input. Connect to LED string anode in boost and buck-boost configuration to get OVP protection during open LED. Bypass it with a sufficient capacitor not to allow IN to go below 6.5V in buck applications. Base Drive for External Bipolar Until Internal Driver Starts Switching for the First Time After Power-Up Compensation Component Connection for the Switching Stage. Connect a suitable RC network to ground. This is the output of the gm amplifier 6 REFI Analog Dimming and Thermal Foldback. The IC sources 50µA current out of this pin. Whenever this pin voltage is > 1.2V, the FB voltage is regulated to internal 200mV reference. Whenever this pin voltage < 1.2V, the FB voltage is regulated to VREFI/6. Leave this pin unconnected to disable this foldback feature. 7 GND Ground 8 FB 9, 10 SOURCE — EP www.maximintegrated.com Current-Sense. This pin includes a 5kI/4pF RC filter at its input to average the current information over the switching cycle. Connect this pin directly to SOURCE. Source of the Internal Switching MOSFET Exposed Pad. Connect EP to the ground plane for heatsinking. Do not use the EP as the only electrical connection to ground. Maxim Integrated │ 5 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Functional Diagram IN 200mV I0 5V 50µA IN I1 1/6 LDO + BANDGAP S 1.2V 5V BG UVLO POK EXT REFI gm 5kI PWMC DRAIN 4pF COMP 0.65V 2VP-P DRIVER CSLIMIT SOURCE OSCILLATOR GND 50ns BLANKING FB IN BG OVP MAX16840 Detailed Description The MAX16840 is an average current-mode control LED driver IC for buck, boost, and buck-boost topologies in low-voltage SSL applications. The IC has an integrated 0.2I (max), 48V switching MOSFET that allows the device to be used in lighting applications for MR16 and other SSL applications. The LED driver uses constantfrequency average current-mode control to control the duty cycle of the integrated switching MOSFET. The IC has all the necessary features required for MR16 lighting applications using LEDs. The IC uses an input-current control scheme to achieve power factor correction. This feature allows the IC to be compatible with electronic transformers and dimmable with trailing-edge (for electronic transformers). www.maximintegrated.com The switch current is sensed on FB. The voltage on FB goes through an RC filter as shown in the Functional Diagram. This voltage is then fed to the negative input of a transconductance amplifier. The positive input of the gm amplifier is the programmed input current level. The output voltage of the gm amplifier is compared with a ramp at the switching frequency to set the duty cycle. The switching frequency is set at 300kHz. The average current-mode controller inside the IC regulates the input current. The IC also features an internal overvoltage protection of 46V on IN to protect the internal switching MOSFET from damage if the LED string is open or if the voltage on the LED string is too high. Maxim Integrated │ 6 MAX16840 The IC has a control pin, REFI, to program the input current. The IC regulates the average voltage on FB to 200mV if REFI is left open. A control voltage on REFI can be used to control the input current. The average voltage on FB is regulated to VREFI/6, where VREFI is the voltage on REFI. The linear control of the FB voltage ceases once the voltage on REFI exceeds 1.2V. Once the voltage increases beyond 1.2V, the voltage on FB is regulated to 200mV. REFI has an internal current source of 50FA and the voltage on REFI can also be set with a resistor to ground on REFI. This pin can also be used with an NTC resistor on the pin to achieve thermal foldback. The IC has a separate EXT pin that can be used to guarantee that there is a kick-start of current at turn-on for low-input voltages for proper operation with electronic transformers. EXT drives an external npn transistor. Once the regulator MOSFET switches for the first time, after the IN voltage has passed the 5.5V UVLO threshold, EXT is pulled to ground and the external npn transistor is turned off. Internal Oscillator The IC has an internal oscillator with a fixed switching frequency of 300kHz. Input Voltage (IN) The IC is powered by the voltage on IN. The operating voltage range on IN is from 6.5V to 48V. An internal UVLO is set at 5.6V. Below 5.4V, there is no switching of the internal power MOSFET and the gate driver for the MOSFET is low. The typical hysteresis of the UVLO threshold is 200mV. There is an internal LDO of 5V that is used to power all the internal circuitry and the gate driver for the internal switching MOSFET. An internal overvoltage protection on IN stops switching once the voltage on IN exceeds 46V. The switching of the internal MOSFET ceases once the rising voltage on IN exceeds 46V and stays off until the voltage on IN drops by 1.2V from the OVP threshold of 46V. www.maximintegrated.com LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps External BJT Driver (EXT) EXT is a separate driver for an external npn transistor that is used to drive an external resistive load when the input voltage on IN is below the UVLO. This is useful for operation with electronic transformers at low-input voltages. The minimum current capability of this pin is 20mA. Internal Switching MOSFET The IC has an integrated switching MOSFET with a maximum RDSON of 0.2I at +125NC. The typical RDSON at +25NC is 0.1I. This allows the IC to be used in a boost LED driver for power levels up to 20W and for buck-boost applications in MR16s for power levels up to 7W. The maximum voltage rating of the MOSFET is 48V operation. The drain of the internal MOSFET is connected to the DRAIN pin and the source of the internal MOSFET is connected to the SOURCE pin. Current Sense (FB) The source of the internal MOSFET is connected to SOURCE, so a current-sense resistor must be connected between SOURCE and ground and the current information is read by FB, so SOURCE must be connected to FB. The set point of the current is determined by REFI. If REFI is left open, the average current-sense voltage on FB is regulated by the IC’s control loop to 200mV. There is a separate peak-limit comparator that terminates switching every cycle if the voltage on FB exceeds 650mV. This comparator has a leading-edge blanking time of 50ns. Control Loop The IC uses an average current-mode control scheme to regulate the input current (Figure 1). The control loop regulates the average voltage on FB. An internal RC filter removes current spikes appearing on this pin. Additional filtering can be added if necessary. The current-regulation loop consists of the current-sense resistor RCS, the RC filter shown in Figure 1, the transconductance error amplifier (gm), an oscillator providing the 300kHz ramp, the control voltage on the positive input of the gm amplifier, and the PWM comparator (PWMC). Maxim Integrated │ 7 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps L1 INPUT COMP RCF CP CZ LED+ MAX16840 CONTROL VOLTAGE gm PWMC 2VP-P DRIVER 5kI 10pF SOURCE FB RCS Figure 1. Control Loop Peak-Limit Comparator Current-Reference Input (REFI) The IC has a peak-limit comparator that limits the peak current in the switching MOSFET. If the current-sense voltage on FB exceeds 0.65V, the peak-limit comparator terminates switching for that switching cycle. This limits the peak current in the switching MOSFET and the inductor during transients. The IC has a current-reference input (REFI). For VREFI > 1.2V, an internal reference sets the input average current to 200mV/RCS. For VREFI < 1.2V, the input current is reduced proportionally to VREFI, and it can be reduced down to zero. The maximum withstand voltage of this input is 6V. REFI has an internal current source of 50FA, and the voltage on REFI can also be set with a resistor to ground on REFI. This pin can also be used with an NTC resistor on the pin to achieve thermal foldback. PWM Comparator The PWM comparator (PWMC) determines the on-time of the switching MOSFET on a cycle-by-cycle basis by comparing the output of the gm amplifier to a 2VP-P ramp signal. At the start of each clock cycle, an RS flip-flop resets and the gate driver turns on the switching MOSFET. The comparator sets the flip-flop as soon as the ramp signal exceeds the COMP voltage, thus terminating the on cycle. www.maximintegrated.com Maxim Integrated │ 8 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps L2 D1 R3 L1 DRAIN BD1 12V AC LED+ REFI EXT C1 IN MAX16840 COMP C3 LED- SOURCE C4 GND FB R1 R2 Figure 2. Boost LED Driver Applications information Boost Configuration In MR16 and other 12V AC input applications, the boost configuration is used when the LED string voltage exceeds 18V. This means that, in general, if the number of LEDs in series in the application is greater than or equal to 6 LEDs, the IC can be used in the boost configuration to provide the best efficiency. Figure 2 shows a boost MR16 application. The number of LEDs can range from 6 to 10 LEDs. The maximum voltage across the LED string should not exceed 40V. In the boost configuration, the current in the inductor is the same as the current in the current-sense resistor R1. Resistor (R1) The current in resistor R1 is the same as the current in inductor L2. If the desired maximum output power with 12V AC at 50Hz or 60Hz is POUT, the input power PIN is given: PIN = POUT/n where n is the efficiency. The input current is given by: IIN = PIN/10.8V Resistor R1 is then given by: R1 = 0.2V/IIN where R1 is in ohms and IIN is in amps. Boost Inductor (L2) For optimum efficiency, the boost inductor must be operating in continuous-conduction mode. The maximum www.maximintegrated.com peak current in the inductor occurs at the peak of the highest input voltage. The P-P ripple at this input voltage is ∆IL. The highest input voltage is 13.2V AC, which is 10% higher than the typical value. The peak current in the inductor is: IPK = IIN + 0.5∆IL The output voltage of the LED string is given by VLED. As a first-order approximation, the LED voltage is assumed constant. The duty cycle at the peak of the input voltage is therefore: 13.2V × 2 18.66V = D MIN = 1− 1− VLED VLED The percentage P-P ripple is typically selected in the 30% to 60% range of the maximum input current. Assuming a 60% P-P inductor-current ripple, the maximum inductor current is given by: IPK = 1.3IINMAX The minimum inductor value is given by: L MIN = 18.66V × D MIN 0.6IINMAX × 300kHz where the switching frequency is 300kHz. The saturation current of the inductor should be higher than P-P and the minimum value of the inductor at IP-P should exceed LMIN. The temperature of the inductor can be in the +90NC to +100NC range in the application and the losses should be estimated at these elevated temperatures. Maxim Integrated │ 9 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Buck-Boost Configuration Boost Diode (D1) A Schottky diode must be used as rectifier diode D1 to reduce power dissipation. The voltage rating of diode D1 must be greater than the maximum output voltage. Choose a diode that minimizes dissipation at temperatures in the +90N to +100NC range. The diode should be selected to minimize reverse leakage at the maximum output voltage while minimizing forward losses when the diode is conducting. In MR16 applications, the buck-boost configuration is used when the number of LEDs is in the 3-to-5 LED range. Figure 3 shows the schematic of a buck-boost LED driver. The maximum voltage on LED+ should not exceed 40V. Resistor (R1) If the desired maximum output power with 12V AC at 50Hz or 60Hz is POUT, the input power PIN is given: Loop Compensation (R2, C4) PIN = POUT/n where n is the efficiency. The input current is given by: The crossover frequency of the loop must be maximized to get the optimum performance. The maximum value of R2 is given by: 2 × 300kHz × L2 R2 MAX in kΩ = R1× VLED × g m IIN = PIN/12V The resistor R1 is then given by: R1 = 0.2V/IIN where R1 is in ohms, VLED is in volts, gm is the transconductance of the error amplifier in FS, and the value of the inductor L2 is in FH. Choose a value of R2 20% lower than the above value. where R1 is in ohms and IIN is in amps. Buck-Boost Inductor (L2) For optimum efficiency, the inductor must be operating in continuous-conduction mode. The maximum peak current in the inductor occurs at the peak of the highest input voltage. The P-P ripple at this input voltage is DIL. The maximum input current occurs at the highest input voltage. Typically, the highest input voltage is 13.2V AC, which is 10% higher than the typical value. The zero from C4, R2 should be placed at: fz = R1× VLED × g m × R2 12V × π × L Therefore, C4 is given by: C4 = 1 2 × π × fz × R2 The peak current in the inductor is: IPK = IINDMIN + 0.5∆IL LEDL2 D1 R3 L1 12V AC C2 LED+ DRAIN BD1 IN REFI EXT C1 MAX16840 COMP C4 SOURCE FB GND R1 R2 Figure 3. Buck-Boost LED Driver www.maximintegrated.com Maxim Integrated │ 10 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps The output voltage of the LED string is given by VLED. As a first-order approximation, the LED voltage is assumed constant. The duty cycle at the peak of the input voltage is, therefore: 13.2V × 2 18.66V = D MIN = 1− 1− V VLED + 13.2V × 2 LED + 18.66V The percentage P-P ripple is typically selected in the 30% to 60% range of the maximum input current. Assuming a 60% P-P inductor-current ripple, the maximum inductor current is given by: IP-P = 1.3IIN The minimum inductor value is given by: L MIN = 18.66V × D MIN 2 0.6IIN × 300kHz where the switching frequency is 300kHz. The saturation current of the inductor should be higher than IP-P and the minimum value of the inductor at IP-P should exceed LMIN. www.maximintegrated.com Output Diode (D1) A Schottky diode must be used as rectifier diode D1 to reduce power dissipation. The voltage rating of diode D1 must be greater than the maximum peak input voltage plus the maximum output voltage. Choose a diode that minimizes dissipation at temperatures in the +90NC to +100NC range. The diode should be selected to minimize reverse leakage at the maximum output voltage while minimizing forward losses when the diode is conducting. Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 10 TDFN-EP T1033+1 21-0137 90-0003 Maxim Integrated │ 11 MAX16840 LED Driver with Integrated MOSFET for MR16 and Other 12V AC Input Lamps Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 12/10 Initial release 1 2/11 Changed minimum temperature to -40°C 2 5/11 Added missing dots in Typical Operating Circuit and Figure 3 3 8/11 Added missing dots in Typical Operating Circuit and Figure 3 and updated PWMC block in Figure 1 4 1 DESCRIPTION Updated Benefits and Features section — 1, 2, 3, 8 1, 10 1, 8, 10 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2015 Maxim Integrated Products, Inc. │ 12