LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 Phase Dimmable Offline LED Driver with Integrated FET Check for Samples: LM3448 FEATURES DESCRIPTION • The LM3448 is an adaptive constant off-time AC/DC buck (step-down) constant current LED regulator designed to be compatible with TRIAC dimmers. The LM3448 provides a constant current for illuminating high power LEDs and includes a phase angle dim decoder.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com Connection Diagram Top View SW 1 16 SW SW 2 15 SW NC 3 14 NC BLDR 4 13 ISNS GND 5 12 GND VCC 6 11 FLTR2 ASNS 7 10 COFF FLTR1 8 9 DIM Figure 2. 16-Lead Narrow SOIC Package PIN DESCRIPTIONS Pin(s) Name Description 1, 2, 15, 16 SW Drain connection of internal 600V MOSFET. 3, 14 NC No connect. Provides clearance between high voltage and low voltage pins. Do not tie to GND. 4 BLDR Bleeder pin.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 ABSOLUTE MAXIMUM RATINGS (1) If Military/Aerospace specified devices are required, contact the Texas Instruments Sales Office/ Distributors for availability and specifications. VALUE / UNIT SW to GND -0.3V to +600V BLDR to GND -0.3V to +17V VCC, FLTR1 to GND -0.3V to +14V ISNS to GND -0.3V to +2.5V ASNS, DIM, FLTR2, COFF to GND -0.3V to +7.0V SW FET Drain Current: Peak 1.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com ELECTRICAL CHARACTERISTICS (1) VCC = 12V unless otherwise noted. Limits in standard type face are for TJ = 25°C and those with boldface type apply over the full Operating Temperature Range ( TJ = −40°C to +125°C). Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = +25ºC and are provided for reference purposes only.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 ELECTRICAL CHARACTERISTICS(1) (continued) VCC = 12V unless otherwise noted. Limits in standard type face are for TJ = 25°C and those with boldface type apply over the full Operating Temperature Range ( TJ = −40°C to +125°C). Minimum and Maximum limits are specified through test, design, or statistical correlation. Typical values represent the most likely parametric norm at TJ = +25ºC and are provided for reference purposes only.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com TYPICAL PERFORMANCE CHARACTERISTICS TJ = 25°C and VCC = 12V unless otherwise specified. Efficiency vs. Input Line Voltage (1) Power Factor vs. Input Line Voltage (1) 0.98 84 7 LEDs 0.97 POWER FACTOR EFFICIENCY (%) 82 80 78 9 LEDs 76 9 LEDs 0.96 0.95 7 LEDs 0.94 74 80 90 100 110 120 130 INPUT VOLTAGE (VRMS) 0.93 80 140 90 100 110 120 130 INPUT VOLTAGE (VRMS) Figure 3. Figure 4. LED Current vs. Input Line Voltage (2) fSW vs.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 TYPICAL PERFORMANCE CHARACTERISTICS (continued) TJ = 25°C and VCC = 12V unless otherwise specified. VCC UVLO vs. Temperature VCOFF Threshold vs. Temperature 1.30 UVLO (VCC) Rising VCOFFTHRESHOLD (V) UVLO THRESHOLD (V) 8.0 7.5 7.0 UVLO (VCC) Falling 6.5 6.0 -50 -25 1.28 1.27 1.26 1.25 0 25 50 75 100 125 150 TEMPERATURE (°C) -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) Figure 9. Figure 10. Angle Detect Threshold vs.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com SIMPLIFIED INTERNAL BLOCK DIAGRAM VCC ANGLE DETECT BLDR LM3448 INTERNAL REGULATORS 4 Ps 7.2V VCC UVLO 230 SW BLEEDER THERMAL SHUTDOWN COFF COFF 1.276V 33: ASNS MOSFET DRIVER S START Q R 0V to 4V LATCH 750 mV 50k DIM DECODER 4.9V PWM 370k Tri-State CONTROLLER FLTR1 RAMP I-LIM DIM RAMP GEN. 5.9 kHz 3V 1V 1.27V 1k ISNS LEADING EDGE BLANKING FLTR2 125 ns GND Figure 14.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 An RC network consisting of R1, R2, and C1 delay the turn on of the TRIAC until the voltage on C1 reaches the trigger voltage of the diac. Increasing the resistance of the potentiometer (wiper moving downward) increases the turn-on delay which decreases the on-time or "conduction angle" of the TRIAC (θ). This reduces the average power delivered to the load. (a) (b) DELAY ? (c) ? DELAY Figure 16.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com V+ (a) t VAC (B) t Figure 17. Voltage Waveforms After Bridge Rectifier Without TRIAC Dimming Figure 18(b) and Figure 18(a) show typical TRIAC dimmed voltage waveforms before and after the bridge rectifier. V+ (a) t VAC (b) t delay , Figure 18.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 V+ R2 Q1 D2 D1 R5 C5 LM3448 U1 9 DIM FLTR1 8 ASNS 7 11 FLTR2 VCC 6 12 GND GND 5 13 ISNS BLDR 4 14 NC NC 3 15 SW SW 2 16 SW SW 1 R1 10 COFF C3 C4 Figure 19. AC Line Sense Circuitry D1 is typically a 15V zener diode which forces transistor Q1 to “stand-off” most of the rectified line voltage.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com The Angle Detect circuit and its filter produce a DC level which corresponds to the duty cycle (relative on-time) of the TRIAC dimmer. As a result, the LM3448 will work equally well with 50Hz or 60Hz line voltages. BLEEDER While the BLDR pin is below the 7.21V threshold, the internal bleeder MOSFET is on to place a small load (230Ω) on the series pass regulator.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 VBUCK R4 C12 D10 LM3448 Q3 U1 9 DIM FLTR1 8 ASNS 7 11 FLTR2 VCC 6 12 GND GND 5 13 ISNS BLDR 4 14 NC NC 3 15 SW SW 2 16 SW SW 1 L2 ICOLL 10 COFF R3 C11 Figure 20. Simplified Buck Regulation Circuit Constant off-time control architecture operates by simply defining the off-time and allowing the on-time, and therefore the switching frequency, to vary as either VIN or VO changes.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com IL2-PK 'iL IAVE IL2-MIN IL2 (t) tON t tOFF Figure 21. Inductor Current Waveform in CCM VCC BIAS SUPPLY The LM3448 requires a supply voltage at the VCC pin in the range of 8V to 12V. The device has VCC undervoltage lockout (UVLO) with rising and falling thresholds of 7.4V and 6.4V respectively. Methods for supplying the VCC voltage are discussed in the “Design Considerations” section of this datasheet.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 VBUCK supplies the power which drives the LED string. Diode D3 allows VBUCK to remain high while V+ cycles on and off. VBUCK has a relatively small hold capacitor C10 which reduces the voltage ripple when the valley-fill capacitors are being charged. However, the network of diodes and capacitors shown between D3 and C10 make up a "valley-fill" circuit. The valley-fill circuit can be configured with two or three stages.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com The valley-fill circuit can be optimized for power factor, voltage hold-up and overall application size and cost. The LM3448 will operate with a single stage or a three stage valley-fill circuit as well. Resistor R8 functions as a current limiting resistor during start-up and during the transition from series to parallel connection. Resistors R6 and R7 are 1MΩ bleeder resistors and may or may not be necessary for each application.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 By using the line voltage injection technique, the FLTR2 pin has the voltage wave shape shown in Figure 26 on it with no TRIAC dimmer in-line. Peak voltage at the FLTR2 pin should be kept below 1.25V otherwise current limit will be tripped. Capacitor C11 is chosen small enough so as not to distort the AC signal but just add a little filtering.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com V+ R3 VCC Q1 D3 D1 R4 C8 C7 LM3448 VCC 6 BLDR 4 Figure 28. Basic holding current circuit OPTIMIZING THE HOLDING CURRENT For optimal system performance and efficiency, only enough holding current should be applied at the right time in the cycle to keep the TRIAC operating properly. This will ensure no variation or ‘flicker’ is seen in the LED light output while improving the circuit efficiency.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 Linear Hold Insertion Circuit This circuit adds holding current during low TRIAC conduction angles. A variable voltage between 0 and 5 volts is generated at the Q6 gate by averaging the square wave output signal on the DIM pin. The duty cycle of this square wave varies with the TRIAC firing angle. As the LEDs are dimmed, the voltage at the Q6 gate will rise pulling a “holding current” equal to the Q6 source voltage divided by resistor R19.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com V+ R3 VCC Q1 D3 D1 R4 C8 C7 LM3448 VCC 6 BLDR 4 Figure 30.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 T1 V+ VLED+ SW VLED- R3 D9 R12 D10 Q1 R17 Q2 C4 R22 D11 D8 D1 C7 R4 C8 LM3448 VCC 6 Figure 31. VCC Auxiliary Winding Bias Circuit COFF CURRENT SOURCE CIRCUITS There are a few different current source circuits that can be used for establishing the LM3448 constant-off time control as shown in Figure 32. Figure 32(a) shows the simplest current source circuit.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com VBUCK ROFF VCC VCC LEDs C1 D1 Q1 D1 ROFF L1 ROFF COFF Q1 SW COFF COFF COFF COFF (a) R1 COFF (b) (c) Figure 32.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 Design Guide V+ VBUCK D3 C7 + D9 BR1 C10 D8 R2 + C9 D4 C12 Q1 TRIAC DIMMER VLED - R4 VLED- D2 VAC D1 D10 R5 Q3 C5 L2 LM3448 U1 9 DIM FLTR1 8 R1 C3 ICOLL ASNS 7 10 COFF 11 FLTR2 VCC 6 12 GND GND 5 13 ISNS BLDR 4 C4 R3 14 NC NC 3 15 SW SW 2 16 SW SW 1 C11 Figure 33.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com With efficiency considered: 1 VLED u K VBUCK D (5) For simplicity, choose efficiency between 75% and 85%. CALCULATING OFF-TIME The “Off-Time” of the LM3448 is set by the user and remains fairly constant as long as the voltage of the LED stack remains constant. Calculating the off-time is the first step in determining the switching frequency (fSW) of the converter, which is integral in determining some external component values.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 The on-time (tON) and therefore the switching frequency, will vary as the VBUCK voltage changes with line voltage. A good design practice is to choose a desired nominal switching frequency knowing that the switching frequency will decrease as the line voltage drops and increase as the line voltage increases. The off-time of the LM3448 can be programmed for switching frequencies ranging from 30 kHz to over 1MHz.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com The equation for an ideal inductor is: v L di dt (16) Given a fixed inductor value, L, this equation states that the change in the inductor current over time is proportional to the voltage applied across the inductor.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 IL2-PK 'iL IAVE IL2-MIN IL2 (t) tON tOFF t Figure 35. Inductor Current Waveform in CCM Knowing the desired average LED current (IAVE) and the nominal inductor current ripple (ΔiL), the peak current for an application running in CCM is defined as follows: iL 2 - P K IA V E ' iL (26) 2 Or, the maximum (i.e.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com 30° 150° tX VBUCK 8.33 ms 0° t 180° Figure 36. Two Stage Valley-Fill VBUCK Voltage with no TRIAC Dimming From Figure 36 and the equation for current in a capacitor, i C dv dt (30) the amount of capacitance needed at VBUCK can be calculated using the following method. At 60Hz and a valley-fill circuit of two stages, the hold-up time (tX) required at VBUCK is calculated as follows.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 The voltage at VBUCK with a valley-fill stage of two will look similar to the waveforms of Figure 38. The purpose of the valley-fill circuit is to allow the buck converter to pull power directly off of the AC line when the line voltage is greater than its peak voltage divided by two (for a two stage valley-fill circuit).
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com OUTPUT CAPACITOR A capacitor placed in parallel with the LED or array of LEDs can be used to reduce the LED current ripple while keeping the same average current through both the inductor and the LED array. With a buck topology the output inductance (L2) can now be lowered, making the magnetics smaller and less expensive. With a well designed converter, you can assume that all of the ripple will be seen by the capacitor and not the LEDs.
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 2. Calculate maximum voltage VBUCK voltage, VB U C K (M A X ) 135 2 190V (39) 3. Calculate tOFF at VBUCK nominal line voltage, tO FF § § 1 2 5 .2 V · · u ¨¨ 1- ¨ ¸ ¸¸ © © 0 .8 1 1 5 2 V ¹ ¹ 3 .2 3 P s (40) 250kH z 4. Calculate tON(MIN) at high line to ensure that – tON(MIN) > 200ns, t O N ( M IN ) § 1 2 5 .2 V · u ¨ ¸ 0 .8 135 2 V ¹ © § § 1 2 5 .2 V · · u ¨¨ 1- ¨ ¸ ¸¸ © © 0 .8 1 3 5 2 V ¹ ¹ u 3 .2 3 P s 638ns (41) 5.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com APPLICATIONS INFORMATION DESIGN #1: 7W, 120VAC Non-isolated Buck LED Driver with Valley-Fill PFC SPECIFICATIONS: • • • AC Input Voltage: 120VAC nominal (85VAC – 135VAC) Output Voltage: 21.
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LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com Table 1. DESIGN #1 BILL OF MATERIALS 34 Part ID Description Manufacturer Part Number U1 IC LED Driver Texas Instruments LM3448MA BR1 Bridge Rectifier Vr = 400V, Io = 0.8A, Vf = 1V Diodes Inc. HD04-T C2 Ceramic, 0.01uF, X7R, 25V, 10% Murata GRM188R71E103KA01D C3 Ceramic, 1000pF 500V X7R 1206 Kemet C1206C102KCRACTU C12 .
LM3448 www.ti.com SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 DESIGN #2: 6.5W, 120VAC Non-isolated “A19 Edison” Retrofit with AC-Coupled Line Injection SPECIFICATIONS: • • • AC Input Voltage: 120VAC nominal (85VAC – 135VAC) Output Voltage: 35.
LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com DESIGN #3: 6W, 120VAC Isolated Flyback LED Driver with Direct Line Injection SPECIFICATIONS: • • • AC Input Voltage: 120VAC nominal (85VAC – 135VAC) Flyback Output Voltage: 27.
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LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com DESIGN #4: 6W, 230VAC Isolated Flyback LED Driver with Direct Line Injection SPECIFICATIONS: • • • AC Input Voltage: 230VAC nominal (180VAC – 265VAC) Flyback Output Voltage: 27.
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LM3448 SNOSB51C – SEPTEMBER 2011 – REVISED MAY 2013 www.ti.com REVISION HISTORY Changes from Revision B (May 2013) to Revision C • 40 Page Changed layout of National Data Sheet to TI format ..........................................................................................................
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PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 TAPE AND REEL INFORMATION *All dimensions are nominal Device LM3448MAX/NOPB Package Package Pins Type Drawing SOIC D 16 SPQ Reel Reel A0 Diameter Width (mm) (mm) W1 (mm) 2500 330.0 16.4 Pack Materials-Page 1 6.5 B0 (mm) K0 (mm) P1 (mm) 10.3 2.3 8.0 W Pin1 (mm) Quadrant 16.
PACKAGE MATERIALS INFORMATION www.ti.com 8-May-2013 *All dimensions are nominal Device Package Type Package Drawing Pins SPQ Length (mm) Width (mm) Height (mm) LM3448MAX/NOPB SOIC D 16 2500 367.0 367.0 38.
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