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LT3799-1

37991f

Isolated PFC LED Driver with Minimum Number of

External Components

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

3799-1 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 LT3799-1 typically achieves power factors

of 0.97. The FAULT pin provides notification of open and

short LED conditions. The LT3799-1 offers improved line

regulation over the LT3799, but is not designed for use

with a TRIAC dimmer.

The LT3799-1 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 Voltage20W 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.

37991 TA01a

20W

LED

POWER

IN_SENSE

DCM

REF

CTRL2

CTRL1

GATE

SENSE

INTV

GND

LT3799-1

FAULT

FAULT COMP

CT COMP

–

560μF

× 2

4.7pF

10μF

2.2nF

4:1:1

0.1μF

20Ω

0.05Ω

499k

100k

6.34k

4.99k

100k

170V

33V

CTRL3

90V

TO 150V

0.22μF

40.2k

32.4k

15.8k

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

37991 TA01b

Summary of content (20 pages)

PAGE 1
LT3799-1 Offline Isolated Flyback LED Controller with Active PFC FEATURES DESCRIPTION n The LT®3799-1 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.
PAGE 2
LT3799-1 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
LT3799-1 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
LT3799-1 TYPICAL PERFORMANCE CHARACTERISTICS VIN Start-Up Voltage vs Temperature Input Voltage Hysteresis vs Temperature VIN IQ vs Temperature 140 24.0 12.0 100 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 22.0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 0 –50 125 50 25 0 75 TEMPERATURE (°C) –25 37991 G01 2.075 2.050 2.050 2.025 2.025 Current Limit vs Temperature NO LOAD 1.975 200μA LOAD 1.950 1.925 1.
PAGE 5
LT3799-1 TYPICAL PERFORMANCE CHARACTERISTICS CT Pin Discharge Current vs Temperature CT Pin Charge Current vs Temperature 200 CT DISCHARGE CURRENT (nA) 10 8 6 4 2 0 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 0.4 190 CT PIN VOLTAGE (V) 12 CT CHARGE CURRENT (μA) CT Pin Low Threshold vs Temperature 180 170 –25 50 25 0 75 TEMPERATURE (°C) 0 –50 125 100 CT Pin High Threshold vs Temperature 10.25 10.4 10.20 NO LOAD INTVCC (V) 10.2 1.2 1.1 100 125 INTVCC vs VIN 10.6 PART ON 10.
PAGE 6
LT3799-1 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 0.80 90 100 110 120 130 VIN (VAC) 140 150 0.
PAGE 7
LT3799-1 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 LT3799-1 control loop, the maximum current does not directly correspond to the VCTRL voltages. VREF (Pin 4): Voltage Reference Output Pin, Typically 2V.
PAGE 8
LT3799-1 BLOCK DIAGRAM VIN D2 R4 s C1 R5 R3 R1 C3 FB C2 L1C L1A R2 R10 9 T1 10 DCM 16 VIN_SENSE D1 VOUT + L1B N:1 C7 VOUT – 11 VIN S&H 6 C4 5 CT FAULT DETECTION A3 INTVCC FAULT + A2 + – C5 ONE SHOT CURRENT COMPARATOR – COMP+ 13 R7 600mV 7 + A8 – 1.
PAGE 9
LT3799-1 OPERATION The LT3799-1 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. Historically, this has been done with an opto-isolator.
PAGE 10
LT3799-1 OPERATION 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%.
PAGE 11
LT3799-1 OPERATION When the VIN_SENSE voltage is connected to a resistor divider of the supply voltage, the current limit is proportional to the supply voltage if COMP+ is held constant. The output of the error amplifier is multiplied with the VIN_SENSE pin voltage. If the LT3799-1 is configured with a fast control loop, slower changes from the VIN_SENSE pin will not interfere with the current limit or the output current. The COMP+ pin will adjust to the changes of the VIN_SENSE.
PAGE 12
LT3799-1 OPERATION 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: N IOUT(MAX) = 2•(1−D) • • 47.
PAGE 13
LT3799-1 OPERATION Sense Resistor Selection Errors Affecting Current Output Regulation 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 . There are a few factors affecting the regulation of current in a manufacturing environment along with some systematic issues.
PAGE 14
LT3799-1 OPERATION Universal Input The LT3799-1 easily operates over the universal input range of 90VAC to 265VAC , but is not limited to this range. Applications with input voltages above 500VAC can be implemented with the LT3799-1. Output current regulation error may be minimized by using two application circuits for the wide input range: one optimized for 120VAC and another optimized for 220VAC .
PAGE 15
LT3799-1 OPERATION Table 1. Predesigned Transformers—Typical Specifications, Unless Otherwise Noted TRANSFORMER SIZE PART NUMBER (L × W × H) LPRI (μH) NPSA (NP:NS:NA) RPRI (mΩ) RSEC (mΩ) MANUFACTURER TARGET APPLICATION (VOUT /IOUT) JA4429 21.1mm × 21.1mm × 17.3mm 400 1:0.24:0.24 252 126 Coilcraft 22V/1A 7508110210 15.75mm × 15mm × 18.5mm 2000 6.67:1:1.67 5100 165 Würth Elektronik 10V/0.4A 750813002 15.75mm × 15mm × 18.5mm 2000 20:1.0:5.0 6100 25 Würth Elektronik 3.8V/1.
PAGE 16
LT3799-1 OPERATION Discontinuous Mode Detection Protection from Open LED and Shorted LED Faults 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 resistor from INTVCC to the DCM pin adds this current.
PAGE 17
LT3799-1 TYPICAL APPLICATIONS Universal 20W LED Driver L2 800μH L1 33mH 90V TO 265V AC BR1 C1 0.068μF C2 0.22μF R3 499k R4 499k R7 100k R6 D2 20Ω R8 100k C4 C5 4.7pF 10μF 4:1:1 R13 2k D3 VIN DCM VIN_SENSE FB R5 3.48k R15 4.99k LT3799-1 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 CMZ5937B T1: COILCRAFT JA4429-AL M1: FAIRCHILD FDPF15N65 FAULT R16 32.
PAGE 18
LT3799-1 TYPICAL APPLICATIONS Universal Input 4W LED Driver L1 3.3mH R20, 10k C1 33nF BR1 L1 3.3mH R21, 10k 90V TO 270V AC L2, 3.3mH C2 68nF R3 499k R4 499k R7 100k R6 D2 20Ω R8 100k C4 C5 4.7pF 10μF 20:5:1 R13 10k D3 VIN DCM VIN_SENSE R5 3.48k FB R15 4.99k LT3799-1 R16 20Ω R9 40.2k CTRL3 GATE CTRL2 SENSE CTRL1 INTVCC R10 22.1k FAULT BR1: DIODES, INC.
PAGE 19
LT3799-1 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 20
LT3799-1 TYPICAL APPLICATION 90V to 305V AC Input 108W LED Driver L3 150μH L1 10mH L2 10mH C1 0.47μF 90V TO 305V AC R10 499k C2 0.47μF R11 499k D1 D3 D2 D4 R5 D5 20Ω R1 249k R2 249k T1 C21 4.7pF R7 2k C3 22μF D6 VIN VIN_SENSE R12 3.09k 3A R3 100k DCM D8 FB R4 4.32k LT3799-1 R6 200k C13 2.2nF 220V Z4 Z2 VREF R18 100k R19 40.2k 108W LED POWER SENSE INTVCC R20 16.9k D1, D2, D3, D4: IN4005 D5, D6: DIODES INC.