7508110210

LT3799 LINER

Document overview

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• PDF pages: 20

Technical content

n Isolated PFC LED Driver with Minimum Number of External Components n TRIAC Dimmable n VIN and VOUT Limited Only by External Components n Active Power Factor Correction (Typical PFC > 0.97) n Low Harmonic Content n No Opto-Coupler Required n Accurate Regulated LED Current (±5% Typical) n Open LED and Shorted LED Protection n Thermally Enhanced 16-lead MSOP Package TYPICAL APPLICATION FEATURES DESCRIPTION Offline Isolated Flyback LED Controller with Active PFC The L T®3799 is an isolated flyback controller with power factor correction specifically designed for driving LEDs. The controller operates using critical conduction mode allowing the use of a small transformer . Using a novel current sensing scheme, the controller is able to deliver a well regulated current to the secondary side without using an opto-coupler . A strong gate driver is included to drive an external high voltage MOSFET . Utilizing an onboard multiplier , the L T3799 typically achieves power factors of 0.97. The FAUL T pin provides notification of open and short LED conditions. The L T3799 uses a micropower hysteretic start-up to efficiently operate at offline input voltages, with a third winding to provide power to the part. An internal LDO provides a well regulated supply for the part’s internal circuitry and gate driver . LED Current vs Input VoltageTRIAC Dimmable 20W LED Driver

APPLICATIONS

n Offline 4W to 100W+ LED Applications n High DC VIN LED Applications L, L T , L TC, L TM, Linear Technology and the Linear logo are registered trademarks and T rue Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners. Patents pending.

3799 TA01a

V IN_SENSE VIN DCM FB VREF CTRL2 CTRL1 GATE SENSE VINTVCC GND L T3799 FAUL TFAUL T COMP+CT COMP– 560µF × 2 4.7pF 10µF 2.2nF 4:1:1 0.1µF 0.1µF 20/uni03A9 20/uni03A9 0.05/uni03A9 499k 499k 100k 100k 200/uni03A9 6.34k 4.99k 100k CTRL3 0.22µF90V TO 150V AC 0.1µF 40.2k32.4k 16.2k 100k NTC 100k 4.7µF VIN (VAC)

0.80 ILED (A)

0.90 1.00 1.10 100 110 130120 140 1.20 0.85 0.95 1.05 1.15 150

3799 TA01b

Electrical Specifications Subject to Change

PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS Operating Temperature Range (Note 2) (Note 1) CTRL1 CTRL2 CTRL3 V REF FAUL T CT COMP+ COMP– V IN_SENSE SENSE GATE INTV CC NC V IN DCM FB TOP VIEW GND MSE PACKAGE 16-LEAD PLASTIC MSOP θJA = 50°C/W , θJC = 10°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE L T3799EMSE#PBF L T3799EMSE#TRPBF 3799 16-Lead Plastic MSOPE –40°C to 125°C L T3799IMSE#PBF L T3799IMSE#TRPBF 3799 16-Lead Plastic MSOPE –40°C to 125°C Consult L TC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container . For more information on lead free part marking, go to: http://www.linear .com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear .com/tapeandreel/

ELECTRICAL CHARACTERISTICS

PARAMETER CONDITIONS MIN TYP MAX UNITS VIN Turn-On Voltage 22.2 23 24.2 V VIN Turn-Off Voltage 11.8 12.3 13.0 V VIN Hysteresis VTURNON – VTURNOFF 10.7 V VIN Shunt Regulator Voltage I = 1mA 25.0 V VIN Shunt Regulator Current Limit 15 mA VIN Quiescent Current Before Turn-On After Turn-On 55 65 75 µA µA INTVCC Quiescent Current Before Turn-On After Turn-On 1.5 1.2 20.0 2.6 µA mA VIN_SENSE Threshold Turn-Off 30 65 90 mV VIN_SENSE Linear Range 0 1.3 V VREF Voltage 0µA Load 200µA Load l l 1.975 1.9555 1.98 2.02 2.02 V V Error Amplifier Voltage Gain ∆VCOMP+/∆VCOMP–, CTRL1 = 1V , CTRL2 = 2V , CTRL3 = 2V 100 V/V Error Amplifier T ransconductance ∆I = 5µA 50 µmhos The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 18V , INTVCC = 11V , unless otherwise noted.

Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: The L T3799E is guaranteed to meet performance specifications from 0°C to 125°C junction temperature. Specifications over the –40°C The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 18V , unless otherwise noted. PARAMETER CONDITIONS MIN TYP MAX UNITS FB Pin Bias Current (Note 3), FB = 1V 100 600 nA CTRL1/CTRL2/CTRL3 Pin Bias Current CTRL/CTRL2/CTRL3 = 1V ±30 nA SENSE Current Limit Threshold 96 100 106 mV SENSE Input Bias Current Current Out of Pin, SENSE = 0V 15 µA Current Loop Voltage Gain ∆VCTRL/ ∆VSENSE, 1000pF Cap from COMP+ to COMP– 21 V/V CT Pin Charge Current 10 µA CT Pin Discharge Current 200 nA CT Pin Low Threshold Falling Threshold 240 mV CT Pin High Threshold Rising Threshold 1.25 V CT Pin Low Hysteresis 100 mV FB Pin High Threshold 1.22 1.25 1.29 V DCM Current Turn-On Threshold Current Out of Pin 45 µA Maximum Oscillator Frequency COMP+ = 1.2V , VIN_SENSE = 1V 300 kHz Minimum Oscillator Frequency COMP+ = 0V , VIN_SENSE 25 kHz Back-Up Oscillator Frequency 20 kHz Linear Regulator INTVCC Regulation Voltage 9.8 10 10.4 V Dropout (VIN – INTVCC) INTVCC = –10mA 500 900 mV Current Limit Below Undervoltage Threshold 17 25 mA Current Limit Above Undervoltage Threshold 80 120 mA Gate Driver tr GATE Driver Output Rise Time CL = 3300pF , 10% to 90% 20 ns tf GATE Driver Output Fall Time CL = 3300pF , 90% to 10% 20 ns GATE Output Low (VOL) 0.05 V GATE Output High (VOH) INTVCC – 0.05 V to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. The L T3799I is guaranteed to meet performance specifications from –40°C to 125°C operating junction temperature. Note 3: Current flows out of the FB pin.

TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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22.0 INPUT VOLTAGE (V)

22.5 23.0 23.5 24.0 TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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IQ (µA) 140 120 100 VIN = 24V VIN = 12V TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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10.0 HYSTERESIS VOLTAGE (V)10.4 10.8 11.2 11.6 12.0 TEMPERATURE (°C) –50

1.900 VREF (V)

1.925 1.975 2.000 2.025 2.100 2.075 0 50 75 1.950 2.050 –25 25 100 125

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200µA LOAD NO LOAD VIN (V) 1.925 1.975 2.000 2.025 2.100 2.075 18 26 28 1.950 2.050 16 2220 24 30 32 200µA LOAD NO LOAD TEMPERATURE (°C) –50 THRESHOLD (mV) 100 120 0 50 75 –25 25 100 125

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TEMPERATURE (°C) –50

225 FREQUENCY (kHz)

–25 25 100 125

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TEMPERATURE (°C) –50 FREQUENCY (kHz) 0 50 75 –25 25 100 125

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TYPICAL PERFORMANCE CHARACTERISTICS VREF vs Temperature VREF vs VIN SENSE Pin Threshold Current vs Temperature Maximum Oscillator Frequency vs Temperature Minimum Oscillator Frequency vs Temperature VIN Start-Up Voltage vs Temperature VIN IQ vs Temperature Input Voltage Hysteresis vs Temperature

TEMPERATURE (°C) –50 9.4 INTVCC (V) 9.6 10.6 10.0 0 50 75 10.2 10.4 9.8 –25 25 100 125

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VIN (V) 9.95 INTVCC (V) 10.00 10.10 10.15 10.20 10.25 14 26 28 10.05 12 1816 2220 24 30 34

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TEMPERATURE (°C) –50 24.50 24.75 25.25 25.50 25.75 26.00 0 50 75 25.00 –25 25 100 125

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VIN SHUNT VOLTAGE (V) ISHUNT = 10mA TEMPERATURE (°C) –50 SHUNT CURRENT (mA) 0 50 75 –25 25 100 125

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TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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CT CHARGE CURRENT (µA) TYPICAL PERFORMANCE CHARACTERISTICS CT Pin High Threshold vs Temperature INTVCC vs Temperature INTVCC vs VIN VIN Shunt Voltage vs Temperature Maximum Shunt Current vs Temperature LED Current vs TRAIC Angle CT Pin Charge Current vs Temperature CT Pin Discharge Current vs Temperature CT Pin Low Threshold vs Temperature TEMPERATURE (°C) –50 0 50 75–25 25 100 125

3799 G10

150 CT DISCHARGE CURRENT (nA)160

TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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CT PIN VOLTAGE (V) 0.1 0.2 0.3 0.4 TEMPERATURE (°C) –50 0 50 75–25 25 100 125

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1.0 CT PIN VOLTAGE (V)

1.1 1.2 1.3 1.4 1.5 TRIAC ANGLE (°C) 0 60 120 15030 90 180

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ILED (A) 0.2 0.4 0.6 0.8 1.2 1.0 220V APPLICATION 120V APPLICATION PAGE 17 SCHEMATIC

TYPICAL PERFORMANCE CHARACTERISTICS LED Current vs Input Voltage LED Current vs Input Voltage LED Current vs Input Voltage Power Factor vs Input Voltage Efficiency vs Input Voltage Power Factor vs Input Voltage Efficiency vs Input Voltage Power Factor vs Input Voltage Efficiency vs Input Voltage VIN (VAC) 0.90 1.00 1.10 100 110 130120 140 1.20 0.85 0.95 1.05 1.15 150

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PAGE 17 SCHEMATIC: OPTIMIZED FOR 120V VIN (VAC) 170 0.90 1.00 1.10 180 190 220210200 240230 250 1.20 0.85 0.95 1.05 1.15 270260

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PAGE 17 SCHEMATIC: OPTIMIZED FOR 220V VIN (VAC) 0.90 1.00 1.10 110 130 190170150 230210 250 1.20 0.85 0.95 1.05 1.15 270

3799 G20

PAGE 17 SCHEMATIC: UNIVERSAL VIN (VAC) 0.92 0.91

0.90 POWER FACTOR ( )

0.94 0.96 0.98 1.00 0.93 0.95 0.97 0.99

3799 G21

PAGE 17 SCHEMATIC: OPTIMIZED FOR 120V VIN (VAC) 170 0.92 0.91 0.94 0.96 0.98 180 190 220210200 240230 250 260 1.00 0.93 0.95 0.97 0.99 270

3799 G22

PAGE 17 SCHEMATIC: OPTIMIZED FOR 220V VIN (VAC) 0.92 0.91 0.94 0.96 0.98 110 130 190170150 230210 250 1.00 0.93 0.95 0.97 0.99 270

3799 G23

PAGE 17 SCHEMATIC: UNIVERSAL VIN (VAC) EFFICIENCY (%) 100

3799 G24

PAGE 17 SCHEMATIC: OPTIMIZED FOR 120V VIN (VAC) EFFICIENCY (%) 100

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170 180 190 220210200 240230 250 260 270 PAGE 17 SCHEMATIC: OPTIMIZED FOR 220V VIN (VAC) EFFICIENCY (%) 100

3799 G26

90 110 130 190170150 230210 250 270 PAGE 17 SCHEMATIC: UNIVERSAL

VIN (Pin 11): Input Voltage. This pin supplies current to the internal start-up circuitry and to the INTVCC LDO. This pin must be locally bypassed with a capacitor . A 25V shunt regulator is internally connected to this pin. INTVCC (Pin 13): Regulated Supply for Internal Loads and GATE Driver . Supplied from VIN and regulates to 10V (typical). INTVCC must be bypassed with a 4.7µF capacitor placed close to the pin. COMP+, COMP– (Pin 7, Pin 8): Compensation Pins for Internal Error Amplifier . Connect a capacitor between these two pins to compensate the internal feedback loop. DCM (Pin 10): Discontinuous Conduction Mode Detection Pin. Connect a capacitor and resistor in series with this pin to the third winding. VIN_SENSE (Pin 16): Line Voltage Sense Pin. The pin is used for sensing the AC line voltage to perform power factor correction. Connect the output of a resistor divider from the line voltage to this pin. The voltage on this pin should be between 1.25V to 1.5V at the maximum input voltage. CTRL1, CTRL2, CTRL3 (Pin 1, Pin 2, Pin 3): Current Output Adjustment Pins. These pins control the output current. The lowest value of the three CTRL inputs is compared to the negative input of the operational amplifier . Due to the unique nature of the L T3799 control loop, the maximum current does not directly correspond to the VCTRL voltages. SENSE (Pin 15): The Current Sense Input for the Control Loop. Kelvin connect this pin to the positive terminal of the switch current sense resistor , RSENSE, and the source of the N-channel MOSFET . The negative terminal of the current sense resistor should be connected to the GND plane close to the IC. GATE (Pin 14): N-Channel MOSFET Gate Driver Output. Switches between INTVCC and GND. This pin is pulled to GND during shutdown state. FB (Pin 9): Voltage Loop Feedback Pin. FB is used to detect open LED conditions by sampling the third winding voltage. An open LED condition is reported if the CT pin is high and the FB pin is higher than 1.25V . CT (Pin 6): Timer Fault Pin. A capacitor is connected between this pin and ground to provide an internal timer for fault operations. During start-up, this pin is pulled to ground and then charged with a 10µA current. Faults related to the FB pin will be ignored until the CT pin reaches 1.25V . If a fault is detected, the controller will stop switching and begin to discharge the CT capacitor with a 200nA pull-down current. When the pin reaches 240mV , the controller will start to switch again. FAUL T (Pin 5): Fault Pin. An open-collector pull-down on FAUL T asserts if FB is greater than 1.25V with the CT pin higher than 1.25V . VREF (Pin 4): Voltage Reference Output Pin, Typically 2V . This pin drives a resistor divider for the CTRL pin, either for analog dimming or for temperature limit/compensation of LED load. Can supply up to 200µA. GND (Exposed Pad Pin 17): Ground. The exposed pad of the package provides both electrical contact to ground and good thermal contact to the printed circuit board. The exposed pad must be soldered to the circuit board for proper operation. PIN FUNCTIONS

VOUT– VIN INTVCC C7L1A FAUL T DETECTION LOW OUTPUT CURRENT OSCILLATOR R Q S S GATE VIN VIN_SENSE L1C DCM 600mV MUL TIPLIER S&H FB SENSE GND 3799 BD DRIVER R7 C5 CT COMP+ FAUL T COMP– CTRL1 CTRL2 VREF SW1 N:1 L1BC3 C2 R10 ONE SHOT A3 1.22V6 CTRL33 1116109

The L T3799 is a current mode switching controller IC designed specifically for generating an average current output in an isolated flyback topology. The special problem normally encountered in such circuits is that information relating to the output voltage and current on the isolated secondary side of the transformer must be communicated to the primary side in order to maintain regulation. Histori- cally, this has been done with an opto-isolator . The L T3799 uses a novel method of using the external MOSFETs peak current information from the sense resistor to calculate the output current of a flyback converter without the need of an opto-coupler . In addition, it also detects open LED conditions by examining the third winding voltage when the main power switch is off. Power factor has become an important specification for lighting. A power factor of one is achieved if the current drawn is proportional to the input voltage. The L T3799 modulates the peak current limit with a scaled version of the input voltage. This technique provides power factors of 0.97 or greater . The Block Diagram shows an overall view of the system. The external components are in a flyback topology con- figuration. The third winding senses the output voltage and also supplies power to the part in steady-state opera- tion. The VIN pin supplies power to an internal LDO that generates 10V at the INTVCC pin. The novel control circuitry consists of an error amplifier , a multiplier , a transmission gate, a current comparator , a low output current oscillator and a master latch, which will be explained in the follow- ing sections. The part also features a sample-and-hold to detect open LED conditions, along with a FAUL T pin. A comparator is used to detect discontinuous conduction mode (DCM) with a cap connected to the third winding. The part features a 1.9A gate driver . The L T3799 employs a micropower hysteretic start-up feature to allow the part to work at any combination of input and output voltages. In the Block Diagram, R3 is used to stand off the high voltage supply voltage. The internal LDO starts to supply current to the INTV CC when VIN is above 23V . The VIN and INTVCC capacitors are charged by the current from R3. When VIN exceeds 23V and INTVCC is in regulation at 10V , the part will began to charge the CT OPERATION pin with 10µA. Once the CT pin reaches 340mV , switching begins. The VIN pin has 10.7V of hysteresis to allow for plenty of flexibility with the input and output capacitor values. The third winding provides power to VIN when its voltage is higher than the VIN voltage. A voltage shunt is provided for fault protection and can sink up to 15mA of current when VIN is over 25V . During a typical cycle, the gate driver turns the external MOSFET on and a current flows through the primary winding. This current increases at a rate proportional to the input voltage and inversely proportional to the magnetizing inductance of the transformer . The control loop determines the maximum current and the current comparator turns the switch off when the current level is reached. When the switch turns off, the energy in the core of the transformer flows out the secondary winding through the output diode, D1. This current decreases at a rate proportional to the output voltage. When the current decreases to zero, the output diode turns off and voltage across the secondary winding starts to oscillate from the parasitic capacitance and the magnetizing inductance of the transformer . Since all windings have the same voltage across them, the third winding rings too. The capacitor connected to the DCM pin, C1, trips the comparator , A2, which serves as a dv/dt detector , when the ringing occurs. This timing information is used to calculate the output current (description to follow). The dv/dt detector waits for the ringing waveform to reach its minimum value and then the switch turns back on. This switching behavior is similar to zero volt switching and minimizes the amount of energy lost when the switch is turned back on, improving efficiency as much as 5%. Since this part operates on the edge of continuous conduction mode and discontinuous conduction mode, this operating mode is called critical conduction mode (or boundary conduction mode). Primary-Side Current Control Loop The CTRL1/CTRL2/CTRL3 pins control the output current of the flyback controller . To simplify the loop, assume the V IN_SENSE pin is held at a constant voltage above 1V , eliminating the multiplier from the control loop. The error amplifier , A5, is configured as an integrator with the external capacitor , C6. The COMP + node voltage is

of the multiplier is proportional to A6 and can be ignored. information available on the primary side of the transformer . time and a height of the peak secondary winding current. described, the input to the integrator is such a waveform. increasing the current comparator input. tional to the supply voltage if COMP + is held constant. will not interfere with the current limit or the output current. The COMP+ pin will adjust to the changes of the VIN_SENSE. but the DC component of the output current is accurate. Figure 1. Secondary Diode Current and Switch Waveforms

3799 F01

MOSFET off when the TRIAC is off, this power device is kept on and sinks the current to properly load the TRIAC. When the TRIAC turns on, the VIN_SENSE pin detects this and enables the loop, but the current comparator is always enabled and turns the switch off if it is tripped. Start-Up The L T3799 uses a hysteretic start-up to operate from high offline voltages. A resistor connected to the supply voltage protects the part from high voltages. This resis - tor is connected to the V IN pin on the part and also to a capacitor . When the resistor charges the part up to 23V and INTVCC is in regulation at 10V , the part begins to charge the CT pin to 340mV and then starts to switch. The resistor does not provide power for the part in steady state, but relies on the capacitor to start-up the part, then the third winding begins to provide power to the VIN pin along with the resistor . An internal voltage clamp is attached to the VIN pin to prevent the resistor current from allowing V IN to go above the absolute maximum voltage of the pin. The internal clamp is set at 25V and is capable of 28mA (typical) of current at room temperature. But, ideally, the resistor connected between the input supply and the VIN pin should be chosen so that less than 10mA is being shunted by this internal clamp. CT Pin and Faults The CT pin is a timing pin for the fault circuitry. When the input voltages are at the correct levels, the CT pin sources 10µA of current. When the CT pin reaches 340mV , the part begins to switch. The output voltage information from the FB pin is sampled but ignored until the CT pin reaches 1.25V . When this occurs, if the FB pin is above 1.25V , the fault flag pulls low. The FAUL T pin is meant to be used with a large pull-up resistor to the INTVCC pin or another supply. The CT pin begins to sink 200nA of current. When the CT pin goes below 240mV , the part will re-enable itself, begin to switch, and start to source 10µA of current to the CT pin but not remove the fault condition. When the CT pin reaches 1.25V and FB is below 1.25V , the FAUL T pin will no longer pull low and switching will continue. If not below 1.25V , the process repeats itself. Programming Output Current The maximum output current depends on the supply voltage and the output voltage in a flyback topology. With the VIN_SENSE pin connected to 1V and a DC supply voltage, the maximum output current is determined at the minimum supply voltage, and the maximum output voltage using the following equation: IOUT(MAX) = 2 • (1− D) • N 42 • RSENSE where D = VOUT • N VOUT • N + VIN The maximum control voltage to achieve this maximum output current is 2V • (1-D). It is suggested to operate at 95% of these values to give margin for the part’s tolerances. When designing for power factor correction, the output current waveform is going to have a half sine wave squared shape and will no longer be able to provide the above currents. By taking the integral of a sine wave squared over half a cycle, the average output current is found to be half the value of the peak output current. In this case, the recommended maximum average output current is as follows: IOUT(MAX) = (1− D) • N 42 • RSENSE

• 47.5% where D = VOUT • N VOUT • N + VIN The maximum control voltage to achieve this maximum output current is (1-D) • 47.5%. For control voltages below the maximum, the output cur- rent is equal to the following equation: IOUT = CTRL • N 42 • RSENSE OPERATION

Figure 2. Correction Factor in Selecting the Figure 3. Output Current Correction Factor

3799 F03

a blanking time of between 600ns and 2.25µs is applied after the switch turns off, depending on the current limit shown in the Leakage Inductance Blanking Time vs Cur- rent Limit curve in the Typical Performance Characteristics section. The detector looks for 40µA of current through the DCM pin due to falling voltage on the third winding when the secondary diode turns off. This detection is important since the output current is calculated using this comparator’s output. This is not the optimal time to turn the switch on because the switch voltage is still close to VIN + VOUT • N and would waste all the energy stored in the parasitic capacitance on the switch node. Discontinuous ringing begins when the secondary current reaches zero and the energy in the parasitic capacitance on the switch node transfers to the input capacitor . This is a second- order network composed of the parasitic capacitance on the switch node and the magnetizing inductance of the primary winding of the transformer . The minimum volt- age of the switch node during this discontinuous ring is VIN – VOUT • N. The L T3799 turns the switch back on at this time, during the discontinuous switch waveform, by sensing when the slope of the switch waveform goes from negative to positive using the dv/dt detector . This switching technique may increase efficiency by 5%. Sense Resistor Selection The resistor , RSENSE, between the source of the external N-channel MOSFET and GND should be selected to provide an adequate switch current to drive the application without exceeding the current limit threshold . For applications without power factor correction, select a resistor according to: RSENSE = 2(1− D)N IOUT • 42 • 95% where D = VOUT • N VOUT • N + VIN For applications with power factor correction, select a resistor according to: RSENSE = (1− D)N IOUT • 42 • 47.5% where D = VOUT • N VOUT • N + VIN Minimum Current Limit The L T3799 features a minimum current limit of approxi- mately 7% of the peak current limit. This is necessary when operating in critical conduction mode since low current limits would increase the operating frequency to a very high frequency. The output voltage sensing circuitry needs a minimum amount of flyback waveform time to sense the output voltage on the third winding. The time needed is 350ns. The minimum current limit allows the use of smaller transformers since the magnetizing primary inductance does not need to be as high to allow proper time to sample the output voltage information. Errors Affecting Current Output Regulation There are a few factors affecting the regulation of current in a manufacturing environment along with some systematic issues. The main manufacturing issues are the winding turns ratio and the L T3799 control loop accuracy. The winding turns ratio is well controlled by the transformer manufacturer’s winding equipment, but most transformers do not require a tight tolerance on the winding ratio. We have worked with transformer manufacturers to specify ±1% error for the turns ratio. Just like any other LED driver , the part is tested and trimmed to eliminate offsets in the control loop and an error of ±3% is specified at 80% of the maximum output current. The error grows larger as the LED current is decreased from the maximum output current. At half the maximum output current, the error doubles to ±6%. There are a number of systematic offsets that may be elimi- nated by adjusting the control voltage from the ideal voltage. It is difficult to measure the flyback time with complete accuracy. If this time is not accurate, the control voltage needs to be adjusted from the ideal value to eliminate the offset but this error still causes line regulation errors. If the supply voltage is lowered, the time error becomes a smaller portion of the switching cycle period so the offset becomes smaller and vice versa. This error may be com- pensated for at the primary supply voltage, but this does

not solve the problem completely for other supply voltages. cannot instantaneously turn off the main power device. so again this affects the line regulation. current line regulation for all three circuits. current while keeping the primary current limit constant. the transformer also stays constant regardless of the NPS. find an optimal MOSFET and diode for a given application. Figure 4. Clamp

3799 F04

be tightly controlled to ensure a consistent output current. negative input and output of the operational amplifier . application, the compensation capacitor is 0.1µF . therefore causing a higher voltage than calculated. Table 1. Predesigned T ransformers—Typical Specifications, Unless Otherwise Noted

The secondary diode stress may be as much as VOUT + 2 • VIN/NPS due to the anode of the diode ringing with the secondary leakage inductance. An RC snubber in parallel with the diode eliminates this ringing, so that the reverse voltage stress is limited to V OUT + VIN/NPS. With a high NPS and output current greater than 3A, the IRMS through the diode can become very high and a low forward drop Schottky is recommended. Discontinuous Mode Detection The discontinuous mode detector uses AC-coupling to detect the ringing on the third winding. A 10pF capacitor with a 500Ω resistor in series is recommended in most designs. Depending on the amount of leakage inductance ringing, an additional current may be needed to prevent false tripping from the leakage inductance ringing. A resis- tor from INTVCC to the DCM pin adds this current. Up to an additional 100µA of current may be needed in some cases. The DCM pin is roughly 0.7V , therefore the resistor value is selected using the following equation: R = 10V − 0.7V I where I is equal to the additional current into the DCM pin. Power Factor Correction/Harmonic Content The L T3799 attains high power factor and low harmonic content by making the peak current of the main power switch proportional to the line voltage by using an internal multiplier . A power factor of >0.97 is easily attainable for most applications by following the design equations in this datasheet. With proper design, L T3799 applications meet IEC 6100-3-2 Class C harmonic standards. OPERATION Protection from Open LED and Shorted LED Faults The L T3799 detects output overvoltage conditions by look- ing at the voltage on the third winding. The third winding voltage is proportional to the output voltage when the main power switch is off and the secondary diode is conducting current. Sensing the output voltage requires delivering power to the output. Using the CT pin, the part turns off switching when a overvoltage condition occurs and re - checks to see if the overvoltage condition has cleared, as described in “CT Pin and Faults” in the Operation section. This greatly reduces the output current delivered to the output but a Zener is required to dissipate 2% of the set output current during an open LED condition. The Zener diode’s voltage needs to be 10% higher than the output voltage set by the resistor divider connected to the FB pin. Multiple Zener diodes in series may be needed for higher output power applications to keep the Zener’s temperature within the specification. During a shorted LED condition, the L T3799 operates at the minimum operating frequency. In normal operation, the third winding provides power to the IC, but the third winding voltage is zero during a shorted LED condition. This causes the part’s VIN UVLO to shutdown switching. The part starts switching again when VIN has reached its turn-on voltage.

3799 TA02

V IN_SENSE VIN DCM FB VREF CTRL2 CTRL1 GATE SENSE VINTVCC GND L T3799 FAUL TFAUL T COMP+CT COMP– C10 560µF × 2 BR1: DIODES, INC. HD06 D1: CENTRAL SEMICONDUCTOR CMR1U-06M D2, D3: DIODES INC. BAV20W DR: CENTRAL SEMICONDUCTOR CMR1U-02M Z1: FAIRCHILD SMBJ170A Z2: CENTRAL SEMICONDUCTOR CMZ5938B T1: COILCRAFT JA4429-AL M1: FAIRCHILD FDPF15N65 4.7pFC5 10µ F 2.2nF 4:1:1 C7, 0.1µF R16 20/uni03A9 20/uni03A9D2 RS 0.05/uni03A9 499k 499k R8 100k 100k 200/uni03A9 R5 3.48k R15 4.99k 100k CTRL3 0.22µF90V TO 265V AC 0.1µF 40.2k R16 32.4k R10 24.9k 100k NTC R18 100k 4.7µF R13 0.1µF BR1 33mH 800µH Universal TRIAC Dimmable 20W LED Driver Component Values for Input Voltage Ranges R5 (Ω) R10 (Ω) RS (Ω) R1 (Ω) C2 (µF) C3 (µF)

3799 TA03

V IN_SENSE VIN DCM FB VREF CTRL2 CTRL1 GATE SENSE VINTVCC GND L T3799 FAUL TFAUL T COMP+CT COMP– C10 1500µF BR1: DIODES, INC. HD06 D1: CENTRAL SEMICONDUCTOR CMR1U-06M D2, D3: CENTRAL SEMICONDUCTOR CMMSHI-100 D4: CENTRAL SEMICONDUCTOR CMSH2-40L Z1: FAIRCHILD SMBJ170A Z2: CENTRAL SEMICONDUCTOR CMZ59198 T1: WÜRTH ELEKTRONIK WE-750813002 M1: FAIRCHILD FQU5N60 4.7pFC5 10µF 2.2nF 20:5:1 0.1µF C7, 0.1µF R16 20/uni03A9 20/uni03A9D2 RS 0.3/uni03A9 499k 499k 100k 100k 750/uni03A9 R5 3.48k R15 4.99k 100k CTRL3 68nF90V TO 265V AC 22nF 40.2k R10 32.4k R18 100k 4.7µF R13 10k 33nF BR1 3.3mH L2, 3.3mH R20, 10k R21, 10k 3.3mH Universal Input TRIAC Dimmable 4W LED Driver

MSOP (MSE16) 0608 REV A 0.53 ± 0.152 (.021 ± .006) SEATING PLANE 0.18 (.007) 1.10 (.043) MAX 0.17 –/uni00A00.27 (.007 – .011) TYP 0.86 (.034) REF 0.50 (.0197) BSC 16151413121110 1 2 3 4 5 6 7 8 1 8 NOTE: 1. DIMENSIONS IN MILLIMETER/(INCH) 2. DRAWING NOT TO SCALE 3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE 5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX 0.254 (.010) 0° – 6° TYP DETAIL “A” DETAIL “A” GAUGE PLANE 5.23 (.206) MIN 3.20 – 3.45 (.126 – .136) 0.889 ± 0.127 (.035 ± .005) RECOMMENDED SOLDER PAD LAYOUT 0.305 ± 0.038 (.0120 ± .0015) TYP 0.50 (.0197) BSC BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ± 0.102 (.112 ± .004) 2.845 ± 0.102 (.112 ± .004) 4.039 ± 0.102 (.159 ± .004) (NOTE 3) 1.651 ± 0.102 (.065 ± .004) 1.651 ± 0.102 (.065 ± .004) 0.1016 ± 0.0508 (.004 ± .002) 3.00 ± 0.102 (.118 ± .004) (NOTE 4) 0.280 ± 0.076 (.011 ± .003) REF 4.90 ± 0.152 (.193 ± .006) DETAIL “B” DETAIL “B” CORNER TAIL IS PART OF THE LEADFRAME FEATURE. FOR REFERENCE ONL Y NO MEASUREMENT PURPOSE

0.12 REF

0.35 REF 16-Lead Plastic MSOP , Exposed Die Pad (Reference L TC DWG # 05-08-1667 Rev A) Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However , no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

Linear Technology Corporation 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear .com  LINEAR TECHNOLOGY CORPORA TION 2011 LT 0211 • PRINTED IN USA RELATED PARTS TYPICAL APPLICATION PART NUMBER DESCRIPTION COMMENTS L T3755/ L T3755-1/ L T3755-2 High Side 60V , 1MHz LED Controller with 3000:1 T rue Color PWM™ Dimming VIN: 4.5V to 40V , VOUT(MAX) = 60V , Dimming: 3000:1 T rue Color PWM, ISD < 1µA, 3mm × 3mm QFN-16 and MSOP-16E Packages L T3756/ L T3756-1/ L T3756-2 High Side 100V , 1MHz LED Controller with 3000:1 T rue Color PWM Dimming VIN: 6V to 100V , VOUT(MAX) = 100V , Dimming: 3000:1 T rue Color PWM, ISD < 1µA, 3mm × 3mm QFN-16 and MSOP-16E Packages L T3743 Synchronous Step-Down 20A LED Driver with Three-State LED Current Control VIN: 5.5V to 36V , Dimming: 10000:1 T rue Color PWM, ISD < 1µA, 5mm × 8mm QFN-52 Package L T3518 2.3A, 2.5MHz High Current LED Driver with 3000:1 Dimming VIN: 3V to 30V , Dimming: 3000:1 T rue Color PWM, ISD < 1µA, 4mm × 4mm QFN-16 Package L T3517 1.3A, 2.5MHz High Current LED Driver with 3000:1 Dimming VIN: 3V to 30V , Dimming: 3000:1 T rue Color PWM, ISD < 1µA, 4mm × 4mm QFN-16 Package L T3741 High Power , Constant-Current, Constant-Voltage Synchronous Step-Down Controller VIN: 6V to 36V , Average Current Mode Control, ISD < 1µA, 4mm × 4mm QFN-20 and TSSOP-20E Packages

3799 TA04

V IN_SENSE VIN DCM FB VREF CTRL2 CTRL1 GATE SENSE VINTVCC GND L T3799 FAUL TFAUL T COMP+CT COMP– C10 390µF × 2 BR1: DIODES, INC. HD06 D1: CENTRAL SEMICONDUCTOR CMR1U-06M D2, D3: DIODES INC. BAV20W D4: DIODES INC. DFLS1150 Z1: FAIRCHILD SMBJ170A Z2: CENTRAL SEMICONDUCTOR CMZ5938B T1: WÜRTH ELEKTRONIK WE750813144 M1: ST MICRO STD12N65M5 4.7pFC5 10µ F 2.2nF 4:1:0.71 0.1µF C7, 0.1µF R16 20/uni03A9 20/uni03A9D2 RS 0.10/uni03A9 499k 499k R8 100k 100k 250/uni03A9 250/uni03A9 3.48k R15 5.90k 100k CTRL3 0.22µF 0.1µF 40.2k R16 10k R10 23.2k PHOTOCELL R17 10k R18 100k 4.7µF R13 BR1 90V TO 265V AC 47nF 39mH 750µH 0.5A Universal Input TRIAC Dimmable 14W LED Driver