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LT3799

3799fa

Isolated PFC LED Driver with Minimum Number of

External Components

TRIAC Dimmable

and V

OUT

Limited Only by External Components

Active Power Factor Correction (Typical PFC > 0.97)

Low Harmonic Content

No Opto-Coupler Required

Accurate Regulated LED Current (±5% Typical)

Open LED and Shorted LED Protection

Thermally Enhanced 16-Lead MSOP Package

Typical applicaTion

FeaTures DescripTion

Offline Isolated Flyback

LED Controller with Active PFC

The LT

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 LT3799 typically achieves power factors

of 0.97. The FAULT pin provides notification of open and

short LED conditions.

The LT3799 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

Offline 4W to 100W+ LED Applications

High DC V

LED Applications

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and

True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Patents pending.

3799 TA01a

20W

LED

POWER

IN_SENSE

DCM

REF

CTRL2

CTRL1

GATE

SENSE

INTV

GND

LT3799

FAULT

FAULT COMP

CT COMP

–

560µF

× 2

4.7pF

10µF

2.2nF

4:1:1

0.1µF

20Ω

0.05Ω

499k

100k

200Ω

6.34k

4.99k

100k

CTRL3

0.22µF

90V

TO 150V

0.1µF

40.2k

32.4k

16.2k

100k

NTC

100k

4.7µF

)

0.80

LED

(A)

0.90

1.00

1.10

100 110 130120 140

1.20

0.85

0.95

1.05

1.15

150

3799 TA01b

Summary of content (20 pages)

PAGE 1
LT3799 Offline Isolated Flyback LED Controller with Active PFC Features n n n n n n n n n Description Isolated PFC LED Driver with Minimum Number of External Components TRIAC Dimmable VIN and VOUT Limited Only by External Components Active Power Factor Correction (Typical PFC > 0.
PAGE 2
LT3799 Absolute Maximum Ratings Pin Configuration (Note 1) VIN, FAULT..................................................................32V GATE, INTVCC............................................................12V CTRL1, CTRL2, CTRL3, VIN_SENSE, COMP–.................4V FB, CT, VREF, COMP+,....................................................3V SENSE.......................................................................0.4V DCM........................................................................
PAGE 3
LT3799 Electrical Characteristics 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.
PAGE 4
LT3799 Typical Performance Characteristics VIN Start-Up Voltage vs Temperature Input Voltage Hysteresis vs Temperature VIN IQ vs Temperature 24.0 12.0 140 100 IQ (µA) INPUT VOLTAGE (V) HYSTERESIS VOLTAGE (V) 120 23.5 23.0 VIN = 24V 80 VIN = 12V 60 40 22.5 11.6 11.2 10.8 10.4 20 –25 50 25 0 75 TEMPERATURE (°C) 100 0 –50 125 3799 G01 2.100 2.075 2.075 2.050 2.050 2.025 2.025 VREF (V) VREF (V) VREF vs Temperature 2.100 2.000 NO LOAD 1.975 200µA LOAD 1.925 1.
PAGE 5
LT3799 Typical Performance Characteristics CT Pin Discharge Current vs Temperature CT Pin Charge Current vs Temperature 200 CT DISCHARGE CURRENT (nA) 8 6 4 2 –25 50 25 0 75 TEMPERATURE (°C) 100 180 170 150 –50 125 1.2 100 10.05 9.6 10.00 3799 G12 25.00 24.75 50 25 0 75 TEMPERATURE (°C) 100 125 3799 G15 100 125 9.95 3799 G13 1.2 25 1.0 20 0.8 15 220V APPLICATION 0.4 5 0.2 50 25 0 75 TEMPERATURE (°C) 100 125 3799 G16 PAGE 17 SCHEMATIC 0.
PAGE 6
LT3799 Typical Performance Characteristics LED Current vs Input Voltage 1.20 PAGE 17 SCHEMATIC: OPTIMIZED FOR 120V 1.15 PAGE 17 SCHEMATIC: OPTIMIZED FOR 220V 1.05 1.05 1.05 ILED (A) 1.10 1.00 PAGE 17 SCHEMATIC: UNIVERSAL 1.15 1.10 1.00 1.00 0.95 0.95 0.95 0.90 0.90 0.90 0.85 0.85 0.85 0.80 170 180 190 200 210 220 230 240 250 260 270 VIN (VAC) 0.80 100 110 120 130 VIN (VAC) 140 150 3799 G18 0.99 0.99 0.98 0.98 0.97 0.97 POWER FACTOR 1.00 0.96 0.95 0.94 0.93 0.92 0.
PAGE 7
LT3799 Pin Functions 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 LT3799 control loop, the maximum current does not directly correspond to the VCTRL voltages. VREF (Pin 4): Voltage Reference Output Pin, Typically 2V.
PAGE 8
LT3799 Block Diagram D2 R4 C1 R5 FB C4 5 CT 10 DCM 16 VIN_SENSE ONE SHOT 3 INTVCC CURRENT COMPARATOR 600mV A7 COMP– CTRL2 L1B N:1 C7 VOUT – – A1 + CTRL3 C5 R8 S S R DRIVER Q MASTER LATCH SW1 +– A5 + + 13 R7 1M 2 + A8 – 1.
PAGE 9
LT3799 Operation gate, a current comparator, a low output current oscillator and a master latch, which will be explained in the following sections. The part also features a sample-and-hold to detect open LED conditions, along with a FAULT 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.
PAGE 10
LT3799 Operation SECONDARY DIODE CURRENT voltage is 120Hz, so the control loop unity gain frequency needs to be set less than approximately 120Hz. Without a large amount of energy storage on the secondary side, the output current is affected by the supply voltage changes, but the DC component of the output current is accurate. IPK(sec) TRIAC Dimming Features SWITCH WAVEFORM TFLYBACK TPERIOD 3799 F01 Figure 1. Secondary Diode Current and Switch Waveforms current and zero during the rest of the cycle.
PAGE 11
LT3799 Operation 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 FAULT 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.
PAGE 12
LT3799 Operation primary winding of the transformer. The minimum voltage of the switch node during this discontinuous ring is VIN – VOUT • N. The LT3799 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%. OUTPUT CURRENT CORRECTION FACTOR 1.16 1.14 1.12 1.10 1.08 1.06 Sense Resistor Selection 1.04 1.02 0 0.
PAGE 13
LT3799 Operation 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 LT3799 control loop accuracy.
PAGE 14
LT3799 Operation the LT3799. Table 1 shows the details of several of these transformers. VSUPPLY Loop Compensation GATE 3799 F03 Figure 3. Clamp Transformer Design Considerations Transformer specification and design is a critical part of successfully applying the LT3799. In addition to the usual list of caveats dealing with high frequency isolated power supply transformer design, the following information should be carefully considered.
PAGE 15
LT3799 Operation by the switch voltage clamp. Always check the switch waveform with an oscilloscope to make sure the leakage inductance voltage spike is below the breakdown voltage of the MOSFET. A transient voltage suppressor and diode are slower than the leakage inductance voltage spike, therefore causing a higher voltage than calculated. 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.
PAGE 16
LT3799 Typical Applications Universal TRIAC Dimmable 20W LED Driver L2 800µH L1 33mH 90V TO 265V AC BR1 C3 0.22µF C1 0.068µF C2 0.1µF R1 200Ω R3 499k R4 499k R7 100k R6 D2 20Ω R8 100k C4 C5 4.7pF 10µF D3 R13 2k VIN DCM VIN_SENSE FB R5 3.48k R18 100k 4:1:1 LT3799 100k NTC R9 40.2k CTRL3 GATE CTRL2 SENSE CTRL1 INTVCC R10 15.4k GND FAULT CT COMP+ FAULT 1A D4 Z1 R15 4.99k VREF R16 32.4k R4 100k R16 20Ω C9 4.7µF C10 560µF ×2 D1 M1 4.02k 20W LED POWER Z2 RS 0.05Ω C8 2.
PAGE 17
LT3799 Typical Applications Universal Input TRIAC Dimmable 4W LED Driver L1 3.3mH R20, 10k 90V TO 265V AC C1 33nF BR1 L1 3.3mH R21, 10k L2, 3.3mH C3 68nF C2 22nF R1 750Ω R3 499k R4 499k R7 100k R6 D2 20Ω R8 100k C4 C5 4.7pF 10µF D3 R13 10k VIN DCM VIN_SENSE FB R5 3.48k R18 100k 20:5:1 LT3799 CTRL3 GATE CTRL2 SENSE CTRL1 INTVCC R10 32.4k FAULT BR1: DIODES, INC.
PAGE 18
LT3799 Package Description Please refer to http://www.linear.com/designtools/packaging/ for the most recent package drawings. MSE Package 16-Lead Plastic MSOP, Exposed Die Pad (Reference LTC DWG # 05-08-1667 Rev D) BOTTOM VIEW OF EXPOSED PAD OPTION 2.845 ± 0.102 (.112 ± .004) 5.23 (.206) MIN 2.845 ± 0.102 (.112 ± .004) 0.889 ± 0.127 (.035 ± .005) 8 1 1.651 ± 0.102 (.065 ± .004) 1.651 ± 0.102 3.20 – 3.45 (.065 ± .004) (.126 – .136) 0.305 ± 0.038 (.0120 ± .0015) TYP 16 0.50 (.0197) BSC 4.039 ± 0.
PAGE 19
LT3799 Revision History REV DATE DESCRIPTION A 01/12 Added “Maximum” to SENSE Current Limit Threshold parameter; Updated Conditions and Typ and Max values for Dropout (VIN – INTVCC) parameter; Changed Current Limit Typ value to 15. PAGE NUMBER 3 Corrected Y-axis lables for G21, G22 and G23. 6 Reordered Pin Functions in numerical order. 7 Removed section title”Setting Control Voltages for LED Over Temperature and Brownout Conditions”.
PAGE 20
LT3799 Typical Application Universal Input TRIAC Dimmable 14W LED Driver L2 750µH L1 39mH 90V TO 265V AC BR1 C1 47nF C2 0.1µF C3 0.22µF R1 250Ω R3 499k R2 250Ω R4 499k R7 100k R6 D2 20Ω R8 100k C4 C5 4.7pF 10µF D3 4:1:0.71 R13 2k VIN DCM VIN_SENSE FB R5 3.48k LT3799 R16 10k R9 40.2k PHOTOCELL R17 10k CTRL3 GATE CTRL2 SENSE CTRL1 INTVCC R10 23.2k GND FAULT CT COMP FAULT C6 0.1µF BR1: DIODES, INC. HD06 D1: CENTRAL SEMICONDUCTOR CMR1U-06M D2, D3: DIODES INC.