EVALUATION KIT AVAILABLE MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming General Description The MAX31840 is an LED driver IC for dimmable 12V MR16, as well as AR111 and other 12V lighting applications. This next-generation MR16 LED driver minimizes BOM count, cost, and board space by integrating a number of value-added functions: deep dimming, bleeder control, constant brightness control, and a boost FET; while significantly improving electronic transformer compatibility with standard trailing-edge dimmers. The MAX31840 is designed for the boost architecture to address 35W and higher-wattage MR16 LED replacement bulbs. The MAX31840 is a high-end MR16 LED driver that incorporates a proprietary circuit that enables deep dimming down to ~1%; an improvement over others that only dim down to 10% or 20%. An integrated bleeder and constant brightness controller enables the MAX31840 to shine, flicker-free, with a broad range of electronic transformers. An optimized compensation circuit and boost FET are integrated to further reduce BOM and board space, simplifying design and saving cost. The MAX31840 is available in an 8-pin, 3mm x 3mm TDFN enhanced power package and is rated over the -40°C to +125°C operating temperature range. Applications ●● 12V MR16 GU5.3 LED Bulb ●● Other 12V LED bulbs (MR11, AR111, 12V Track Lighting) 19-100100; Rev 0; 6/17 Benefits and Features ●● High Integration Saves PCB Space and BOM Costs • 36V Boost N-Channel DMOS FET • Bleeder FET Control • Deep Dimming Control • Constant Brightness Control • Internal Compensation • LED Overvoltage Protection • Overcurrent and Overtemperature Protection ●● High-Performance for New LED Dimming Requirements • Meets California Title 24 Part 6 JA8 • Flickering < 30% • > 0.9 Power Factor • Dimming to <1% Brightness, Depending on LEDs • Tight LED Current Regulation of 2% Typical Ordering Information appears at end of data sheet. MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Simplified Block Diagram INPUT 12V/0.5A D1 L1 100uH/1.2A LED7 IN LED6 5.6V R6 UV 26V OV 5V BIAS LED5 R4 2ohm 1W 560ohm ACREC C1 0.22uF 25V DRAIN DEEP DIMMING PWM DCDC NFET AVDET C5 1uF 6.3V C3 22uF 35V LED4 SOURC E LED3 MAX BRIGHTNESS CSA LED2 CS BGT M1 NDS351AN BLEED 0.5V MAX31840 BSRC R2 LED1 0.2V R1 0.2ohm GND (EP) 0.5ohm www.maximintegrated.com Maxim Integrated │ 2 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Absolute Maximum Ratings IN, DRAIN to GND.................................................-0.3V to +36V ACREC to GND......................................................-0.3V to +26V AVDET, BGT, BSRC to GND....................................-0.3V to +6V CS, SOURCE to GND.............................................-0.3V to 1.5V Maximum RMS Current Through DRAIN and SOURCE.......±1A Continuous Power Dissipation (TA = +70°C) TDFN (derate 23.8mW/°C above +70°C).............................1904mW Any Pin to Any Pin ESD Rating................................ ±2kV(HBM) Operating Temperature Range.......................... -40°C to +125°C Maximum Junction Temperature......................................+150°C Storage Temperature Range............................. -65°C to +150°C Lead Temperature (soldering, 10s).................................. +300°C Soldering Temperature (reflow)........................................+260°C 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. Package Information 8 TDFN-EP PACKAGE CODE T833+3 Outline Number 21-0137 Land Pattern Number 90-0059 Thermal Resistance, Single-Layer Board: Junction to Ambient (θJA) 54 Junction to Case (θJC) 8 Thermal Resistance, Four-Layer Board: Junction to Ambient (θJA) 42 Junction to Case (θJC) 8 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 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. Electrical Characteristics (VIN = VACDEC = 12V; VACREC = VSOURCE = VCS = VGND = 0V; 1kΩ from DRAIN to IN, 100kΩ from BSRC to BGT; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1 ) PARAMETER Operating Voltage Range SYMBOL VIN CONDITIONS Guaranteed by Undervoltage Lockout and IN Overvoltage Protection MIN 6.5 When MOSFET fully on, VCS = 0. IN Supply Current Undervoltage Lockout IIN UVLOIN When MOSFET switching at 60% duty, refers to Typical Application Circuit, when VLED/VACREC = 30V/12V, measure IN current IN rising, when DRAIN goes low 5 UVLO Hysteresis IN Overvoltage Protection www.maximintegrated.com MAX UNITS 26 V 1 2.3 1.5 3.2 5.6 6.1 200 VOVP IN rising, when DRAIN goes high 34.8 IN Overvoltage Hysteresis Switching Frequency TYP 35.9 630 700 V mV 37 1.15 Switching frequency at DRAIN mA V V 770 kHz Maxim Integrated │ 3 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Electrical Characteristics (continued) (VIN = VACDEC = 12V; VACREC = VSOURCE = VCS = VGND = 0V; 1kΩ from DRAIN to IN, 100kΩ from BSRC to BGT; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1 ) PARAMETER SYMBOL CS Average Voltage Power Switch On-Resistance Switch Leakage Current RDSON ILEAK MIN TYP MAX TA = +25°C CONDITIONS 196 200 204 -40°C ≤ TA ≤ +125°C 190 210 UNITS mV IDS = 1A 100 200 mΩ VDRAIN = 36V, TA = 25°C 0.01 20 μA DRAIN Rise Time tRDRAIN IDS = 1A 10 ns DRAIN Fall Time tFDRAIN IDS = 1A 10 ns SOURCE Limit Threshold VSOURCETH SOURCE connected to CS 0.66 SOURCE Current-Limit Comparator Propagation Delay CS Input Bias Current ICS VCS = 0V and VCS = 0.3V, TA = 25°C -1 Temperature rising Thermal Shutdown Hysteresis ACREC Input Threshold VACREC ACREC Constant Brightness Center Point VTHAVREC ACREC Constant Brightness Range Bleeder Startup Pulse CS Bleeder Enable Threshold Deep Dim Delay BGT Output Voltage 0.78 25 Thermal-Shutdown Temperature BSRC Voltage 0.72 tOS VTHBLEEDER tDIM ns +1 μA 165 °C 15 °C ACREC rising 3.5 3.8 4.2 V VACREC when VCS = 0.2V (constant brightness center point) 11.4 12 12.6 V 12 ±15% Where LED brightness is held constant VBSRC V Bleeder in regulation 0.475 From ACREC rising to BGT falling CS Rising. When CS falling VBSRC goes low, 100mV (typ) hysteresis From ACREC high to boost off 0.525 75 186 tACREC = 2ms tACREC = 4ms 0.5 V 200 V μs 214 mV 3.9 ms 0.9 3.3 tACREC = 6ms 3.6 6.3 BSRC < 0.5V, output high 1 5.2 BSRC > 0.5V, output low 0 0.5 V Note 1: All devices are 100% tested at TA = TJ = +25°C. Limits over temperature are guaranteed by design. www.maximintegrated.com Maxim Integrated │ 4 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) IQ vs. VIN IQ vs. TEMPERATURE toc01 1.5 1.18 VIN = 32V 1.4 Temp = 25°C 1.16 1.3 1.14 IQ (mA) IQ (mA) toc02 1.2 1.2 1.12 1.1 1.1 1.08 1 1.06 1.04 0.9 1.02 1 0.8 -50 0 50 100 10 150 15 20 25 30 35 VIN (V) TEMPERATURE (°C) UVOL vs. TEMPERTURE FREQUENCY vs. TEMPERATURE toc03 705 toc04 5.7 701 5.65 699 697 UVLO (V) OSCILLATION FREQUENCY (kHz) 703 695 5.6 693 691 5.55 689 687 5.5 685 -50 0 50 -50 100 0 TEMPERATURE (°C) VCS vs. VACREC 90 OUTPUT CONNECTS TO A STRING OF 10 HBLED 360 80 200 190 180 340 70 ILED (mA) DIMMING PHASE (%) 220 VCS (mV) toc07 380 toc06 100 230 210 60 50 30 280 260 10 160 7 9 11 AVERAGE VACREC (V) www.maximintegrated.com 13 15 320 300 40 20 170 100 LED CURRENT vs. AVERAGE VACREC DIMMING PHASE vs. INPUT PHASE toc05 240 50 TEMPERATURE (°C) 240 0 0 20 40 60 INPUT PHASE (%) 80 100 7 9 11 13 AVERAGE VACREC (V) Maxim Integrated │ 5 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Pin Configuration DRAIN 1 + ACREC 2 IN 3 AVDET 4 8 SOURCE 7 CS 6 BGT 5 BSRC MAX31840 EP/GND TDFN Pin Description PIN NAME 1 DRAIN Drain of the Internal Switching MOSFET FUNCTION 2 ACREC Rectified AC Voltage Sensing. Connect this pin to positive side of the rectified AC waveform. Also, connect a bypass capacitor to ground. The zero crossing and dimmer phase information are detected and used to drive an external bleeding FET. 3 IN Input. Connect to LED string anode to get OVP protection during open LED. Also, input to internal supplies. Bypass it with a 150µF capacitor. Also need a bootstrap diode from rectified input to jump-start internal digital circuit. 4 AVDET Average AC Voltage Detection. Connect a bypass capacitor to ground for the constant power circuit. This pin is connected to an internal voltage controlled current source. 5 BSRC Bleeder FET Source Connection. Connect to the source of an NMOS FET for precise bleeding current level control. 6 BGT 7 CS 8 SOURCE - GND Bleeder FET Gate Connection. Connect to the gate of an NMOS FET to supplement input current to maintain electronic transformer operation. Current Sense. This pin includes a 5kΩ/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 Ground via the exposed pad. Functional Diagram Internal Functional Block Refer to the Simplified Block Diagram. www.maximintegrated.com Maxim Integrated │ 6 MAX31840 Detailed Description The MAX31840 is an average current-mode-control LED driver IC for boost topology in low-voltage SSL applications. The IC has an integrated 0.2Ω (max), 36V switching MOSFET that allows the device to be used in lighting applications for MR16 and other SSL applications. The LED driver uses constant-frequency, average currentmode control to control the duty cycle of the integrated switching MOSFET. The IC has all the necessary features required for LED MR16 lighting applications. The IC uses an input-current-control scheme to achieve power factor correction. The IC turns on an external bleeder when the boost operation is off. This feature allows the IC to be compatible with electronic transformers and trailing-edge dimmers (for electronic transformers). The switch current is sensed on CS. The voltage on CS goes through an internal RC filter. 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 amplifier is compared with a ramp at the switching frequency to set the duty cycle. The switching frequency is set at 700kHz. The average current-mode controller inside the IC regulates the input current. The IC also features an internal overvoltage protection of 36V on IN to protect the internal switching MOSFET from damage if the LED string is open or if the voltage is too high. The IC regulates the average voltage on CS to 200mV. The average input current is determined by the value of the resistor connected from the CS pin to ground. To keep the input power almost constant for line-voltage variation of ±13%, a constant brightness circuit has been integrated into the MAX31840. The rectified AC supply after a RC filter, consists of an internal resistor in conjunction with the capacitor connected from the AVDET pin to ground, is used to sense the average voltage level. The IC has a bleeder gate (BGT) ping and a bleeder source (BSRC) pin for the control of an external bleeder N-channel MOSFET. A bleeder is required to draw current after each AC zero-crossing cycle when the boost converter just get started. The same bleeder is also used to provide deep dimming. The bleeder driving circuit inside the IC maintains the BSRC pin at 0.5V. The bleeder current is determined by the value of the resistor connected from the BSRC pin to the ground. Internal Oscillator The IC has an internal oscillator with a fixed switching frequency of 700kHz. 700kHz was chosen to balance between inductor size and EMI emission. www.maximintegrated.com MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Input Voltage (IN) The IC is powered by the voltage on IN and needs to be maintained within the operating voltage range of from 6.5V to 35V. 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. The switching of the internal MOSFET ceases once the rising voltage on IN exceeds 35V and stays off until the voltage on IN drops by 1.2V. Rectified AC (ACREC) The ACREC pin senses the zero crossings for the external bleeder driver. The ACREC pin is also used to detect the dimmer phase to drive the same shared external bleeder FET. The zero crossing bleeding happens at every AC zero crossing and lasts a very short time duration. For deep dimming, an internal circuit detects the time duration of the dimming phase per a half AC period. It then turns off the the boost controller at a shorter duration according to the dimming phase for the next half AC period. The smaller the dimming phase the shorter the duration. At around 15° of dimming phase, the deepest dimming is reached per R4 and C1 values on the ACREC pin. For both zero crossing and deep dimming, the bleeder FET is turned on when the LED boost is off, to maintain a minimum input loading on the electronic transformer. The deep dimming control is capable of delivering <1% of maximum power to the LEDs. External Bleeder Driver (BGT/BSRC) The BGT and BSRC pins drive an external N-channel MOSFET for both zero crossing and deep dimming bleeding. A resistor at the BSRC pin to ground is used to configure the electronic transformer loading current during either zero cross and deep dimming. With 0.5V of source voltage, and a 0.5Ω resistor from source to GND, the bleeder would draw 1A from the input when the ACREC voltage is high and the boost regulator is off. Internal Switching MOSFET The IC has an integrated switching MOSFET with a maximum RDSON of 200mΩ at +125°C. The typical RDSON at +25°C is 100mΩ. This allows the IC to be used in a boost LED driver for power levels up to 12W. The maximum voltage rating of the MOSFET is 36V 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. Maxim Integrated │ 7 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Current Sense (CS) RC filter, the transconductance error amplifier (gm), the internal compensation circuits, an oscillator providing the 700kHz ramp, the control voltage on the positive input of the gm amplifier, and the PWM comparator (PWMC). The source of the internal MOSFET is connected to SOURCE. A current-sense resistor must be connected between SOURCE and ground to set the regulated average input current. The current information is read by CS, so SOURCE must be connected to CS. The set point of the current is determined by the IC's control loop and is nominally 200mV. With a 200mΩ RCS resistor, the average input current will be set to 1A. There is a separate peak-limit comparator that terminates switching every cycle if the voltage on CS exceeds 720mV. This comparator has a leading-edge blanking time of 50ns. This limits the peak current in the switching MOSFET and the inductor during transients to 3.6A when the average current is set to 1A. Peak-Limit Comparator The IC has a peak-limit comparator that limits the peak current in the switching MOSFET. If the current-sense voltage on CS exceeds 0.72V, the peak-limit comparator terminates switching for that switching cycle. This limits the peak current in the switching MOSFET and the inductor during transients. 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. Control Loop The IC uses an average current-mode control scheme to regulate the input current. The control loop regulates the average voltage on CS. An internal RC filter removes current spikes appearing on this pin. The current-regulation loop consists of the current-sense resistor RCS, the internal INPUT D1 L1 LED+ CONTROL VOLTAGE DRAIN gm PWMC INTERNAL COMPENSATION DRIVER NFET SOURC E 2VP_P CS 10pF LED- 5kΩ RCS Figure 1. Control Loop www.maximintegrated.com Maxim Integrated │ 8 MAX31840 Deep Dimming Controlled by the same dimmer, a Halogen bulb appears to be more dim-able compared with a LED replacement. The brightness of a Halogen bulb is proportional to the cube of the average voltage across its inputs. Figure 2 shows the supply waveform of a typical electronic transformer with an oscillation frequency of 20kHz for a duration of a half 60Hz AC cycle. The red and blue curves show minimum and maximum dimmer phases of 12% to 70%, respectively. By calculating the area under these curves, we can find that the corresponding average voltage variation is 13:100. For this voltage variation ratio, the brightness variation for a Halogen bulb is about 0.2:100. For the LED MR16 LED Driver with Integrated Control MOSFET and Deep Dimming replacement, the brightness variation is only 13:100 since its brightness is linearly proportional to the average voltage across it. The deep dimming circuit inside the MAX31840 starts to cut down the LED on duration at dimming phase of about 60%. It eventually cuts down the LED-On duration to a minimum at an input phase of about 15%. Since the brightness is determined by the input duty and the sinusoidal input voltage, the deep dimming profile is more gradual at both low and high duties, as seen in Figure 3. The MAX31840 controls the boost regulator and bleeder to maintain continuous input current, while lowering the power delivered to the LED’s, in order to achieve this dimming profile. Figure 2. Typical Trailing-Edge Dimming Phase Variation www.maximintegrated.com Maxim Integrated │ 9 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Figure 3. Deep Dimming Effect vs. Dimming Phase of A Dimmer www.maximintegrated.com Maxim Integrated │ 10 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Applications Information Boost Configuration For MR16 and other 12V AC input applications, this MAX31840 boost controller is used for the LED strings with forward voltage exceeds 18V. The number of LEDs can range from 6 to 10 LEDs depending on the forward voltage. The maximum voltage across the LED string should not exceed 34V. In this 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 L1. 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/12V Resistor R1 is then given by: R1 = 0.2V/IIN where R1 is in ohms and IIN is in amps. Boost Inductor (L1) For optimum efficiency, the boost 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 peak to peak ripple at this input voltage is ΔIL. The highest input voltage is 13.2V AC, which is 10% higher than the typical value. The peak current in the inductor is: The percentage peak to peak ripple is typically selected in the 30% to 60% range of the maximum input current. Assuming a 60% peak to peak inductor-current ripple, the maximum inductor current is given by: IPK = 1.3IINMAX The minimum inductor value is given by: 18.66V × DMIN LMIN = 0.6I INMAX × 700kHz where the switching frequency is 700kHz. The saturation current of the inductor should be higher than peak to peak and the minimum value of the inductor at IP-P should exceed LMIN. The temperature of the inductor can be in the +90°C to +100ºC range in the application and the losses should be estimated at these elevated temperatures. 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 +90°C to +100°C range. The diode should be selected to minimize reverse leakage at the maximum output voltage while minimizing forward losses when the diode is conducting. Resistor (R2) The current in resistor R2 is the same as the bleeding current for both zero cross and deep dimming. The source voltage is regulated at 0.5V. The current through R2 is given: IR2 = 0.5/R2 IPK = IIN + 0.5ΔIL 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: Or the resistor value is dependent on the desired bleeding current by: R2 = 0.5/IR2 DMIN = 1 − V √ = 1 − V LED LED 13.2 × 2 www.maximintegrated.com 18.66V Maxim Integrated │ 11 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Typical Application Circuit Boost for 50W MR16 Bulb Application D3 12V AC FROM AN ELECTRONIC TRANSFORMER T4 D2 C2 4700pF 25V D1 L1 R6 R4 2Ω 1W 560Ω 100µH/1.2A VLP8040T T1 R3 100Ω LED8 LED7 ACREC IN LED6 C4 C1 0.22µF 25V MB16S DRAIN AVDET 0.1µF 50V C3 C5 150µF 35V MAX31840 1µF LED5 LED4 M1 T2 IRLML2502 SOURCE BGT LED3 BSRC R2 0.5Ω CS LED2 GND (EP) LED1 T3 R1 0.2Ω Ordering Information PART NUMBER MAX31840ATA+ TEMP RANGE PIN-PACKAGE -40°C to +125°C 8 TDFN-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. www.maximintegrated.com Maxim Integrated │ 12 MAX31840 MR16 LED Driver with Integrated Control MOSFET and Deep Dimming Revision History REVISION NUMBER REVISION DATE 0 6/17 DESCRIPTION Initial release PAGES CHANGED — 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. © 2017 Maxim Integrated Products, Inc. │ 13