LM3445-208277EV/NOPB National Semiconductor, LM3445-208277EV/NOPB Datasheet
LM3445-208277EV/NOPB
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LM3445-208277EV/NOPB Summary of contents
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... Triac Dimmable Offline LED Driver General Description The LM3445 is an adaptive constant off-time AC/DC buck (step-down) constant current controller designed to be com- patible with triac dimmers. The LM3445 provides a constant current for illuminating high power LEDs and includes a triac dim decoder. The dim decoder allows wide range LED dim- ming using standard triac dimmers ...
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... Pull above 4.9V (typical) to tri-state DIM DIM Input/output dual function dim pin. This pin can be driven with an external PWM signal to dim the LEDs. It may also be used as an output signal and connected to the DIM pin of other LM3445s or other LED drivers to dim multiple LED circuits simultaneously COFF OFF time setting pin ...
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... Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. BLDR to GND V , GATE, FLTR1 to GND CC ISNS to GND ASNS, DIM, FLTR2, COFF to GND COFF Input Current Continuous Power Dissipation (Note 2) Electrical Characteristics over the full Operating Temperature Range ( T design, or statistical correlation ...
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Symbol Parameter CURRENT SENSE COMPARATOR V FLTR2 open circuit voltage FLTR2 R FLTR2 impedance FLTR2 V Current sense comparator offset voltage OS GATE DRIVE OUTPUT V GATE high saturation DRVH V GATE low saturation DRVL I Peak souce current DRV ...
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Typical Performance Characteristics f vs Input Line Voltage SW BLDR Resistor vs Temperature Min On-Time ( Temperature ON Efficiency vs Input Line Voltage 30060304 V UVLO vs Temperature CC 30060306 Off Threshold (C11) vs Temperature 30060308 5 30060305 ...
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Normalized Variation www.national.com over V Voltage Leading Edge Blanking Variation Over Temperature BUCK 30060310 6 30060372 ...
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Simplified Internal Block Diagram FIGURE 1. Simplified Block Diagram 7 30060311 www.national.com ...
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... Application Information FUNCTIONAL DESCRIPTION The LM3445 contains all the necessary circuitry to build a line- powered (mains powered) constant current LED driver whose output current can be controlled with a conventional triac dim- mer. OVERVIEW OF PHASE CONTROL DIMMING A basic "phase controlled" triac dimmer circuit is shown in Figure 2 ...
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... Theory of Operation Refer to figure 4 below which shows the LM3445 along with basic external circuitry. FIGURE 4. LM3445 Schematic 9 30060301 www.national.com ...
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... As the number of LM3445 circuits is added to a single dimmer, the holding resistor R5’s resistance can be in- creased. A few triac dimmers will require a resistor as low as 1 kΩ or lower for a single LM3445 circuit. The trade-off will be 10 30060317 ...
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... The Angle Detect circuit and its filter produce a DC level which corresponds to the duty cycle (relative on-time) of the triac dimmer result, the LM3445 will work equally well with 50Hz or 60Hz line voltages. BLEEDER While the BLDR pin is below the 7.21V threshold, the bleeder MOSFET place a small load (230Ω ...
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... The valley-fill circuit can be optimized for power factor, volt- age hold up and overall application size and cost. The LM3445 will operate with a single stage or a three stage val- ley-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 1 MΩ ...
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... At some point in time, the inductor current reaches a maximum (I ) determined by the voltage sensed at R3 and L2-PK the ISNS pin. This sensed voltage across R3 is compared FIGURE 11. LM3445 Buck Regulation Circuit against the voltage of dim decoder output, FLTR2, at which point Q2 is turned off by the controller changes. ...
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... MASTER/SLAVE OPERATION Multiple LM3445s can be configured so that large strings of LEDs can be controlled by a single triac dimmer. By doing so, smooth consistent dimming for multiple LED circuits is achieved. When the FLTR1 pin is tied above 4.9V (typical), preferably to VCC, the ramp comparator is tri-stated, disabling the dim decoder ...
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MASTER/SLAVE CONNECTION DIAGRAM MASTER/SLAVE BLOCK DIAGRAMS FIGURE 14. Master/Slave configuration with Separate Valley-Fill Circuits FIGURE 13. Master Slave Configuration 15 30060326 30060327 www.national.com ...
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FIGURE 15. Master/Slave configuration with One Valley-Fill Circuit THERMAL SHUTDOWN Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature exceeds www.national.com 165°C. After thermal shutdown occurs, the output switch doesn’t turn on ...
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... With efficiency considered: For simplicity, choose efficiency between 75% and 85%. CALCULATING OFF-TIME The “Off-Time” of the LM3445 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 determin- ing the switching frequency of the converter, which is integral in determining some external component values ...
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... The off-time of the LM3445 can be programmed for switching frequencies ranging from 30 kHz to over 1 MHz. A trade-off between efficiency and solution size must be considered when designing the LM3445 application. The maximum switching frequency attainable is limited only by the minimum on-time requirement (200 ns). Worst case scenario for minimum on time is when V ...
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... SETTING THE LED CURRENT The LM3445 constant off-time control loop regulates the peak inductor current (I ). The average inductor current equals the L2 average LED current (I ). Therefore the average LED cur- AVE rent is regulated by regulating the peak inductor current. FIGURE 18. Inductor Current Waveform in CCM Knowing the desired average LED current, I inal inductor current ripple, Δ ...
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... See “ Design Example" section for further calculations of the valley-fill capacitors. Determining Maximum Number of Series Connected LEDs Allowed: The LM3445 is an off-line buck topology LED driver. A buck converter topology requires that the input voltage (V the output circuit must be greater than the voltage of the LED stack (V ) for proper regulation ...
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... The average current rating should be greater than: I DS-MAX RE-CIRCULATING DIODE The LM3445 Buck converter requires a re-circulating diode D10 (see the Typical Application circuit figure 4) to carry the inductor current during the MOSFET Q2 off-time. The most efficient choice for D10 is a diode with a low forward drop and ...
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Design Example The following design example illustrates the process of cal- culating external component values. Known: 1. Input voltage range (90V – 135V AC 2. Number of LEDs in series = 7 3. Forward voltage drop of a single LED ...
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... LM3445 Design Example 1 Input = 90V to 135V LED String Application @ 400 mA LED 23 30060369 www.national.com ...
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... Resistor, 1812, 0.0Ω Resistor, 0603, 0.0Ω Resistor, 0603, 1%, 33.2 kΩ Resistor, 0603, 1%, 2.0 kΩ Resistor, 0805, 1%, 3.3 MΩ Terminal Block 2 pos Fuse, 125V, 1,25A 24 Mfr Mfr PN NSC LM3445MM DiodesInc HD04-T Panasonic ELF-11090E Coilcraft MSS1260-474-KLB Coilcraft MSS1260-105KL-KLB Steward HI1206T161R-10 Panasonic ...
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Physical Dimensions inches (millimeters) unless otherwise noted For Ordering, Refer to Ordering Information Table For Ordering, Refer to Ordering Information Table MSOP-10 Pin Package (MM) NS Package Number MUB10A SOIC-14 Pin Package (M) NS Package Number M14A 25 www.national.com ...
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