LT3475 LINER [Linear Technology], LT3475 Datasheet
LT3475
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LT3475 Summary of contents
Page 1
... The constant switching frequency combined with low-impedance ceramic capacitors result in low, predictable output ripple. With its wide input range 36V, the LT3475/LT3475-1 regulate a broad array of power sources. A current mode PWM architecture provides fast transient response and cycle-by-cycle current limiting. Frequency foldback and thermal shutdown provide additional protection ...
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... C T SHDN Pin ...................................................................V Maximum Junction Temperature (Note 2)............. 125°C Operating Temperature Range (Note 3) LT3475E/LT3475E-1 ............................. –40°C to 85°C LT3475I/LT3475I-1 ............................. –40°C to 125°C Storage Temperature Range ................... –65°C to 150°C Lead Temperature Range (Soldering, 10 sec) ....... 300°C ORDER INFORMATION LEAD FREE FINISH ...
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... I =1.5A SW Note 3: The LT3475E and LT3475E-1 are guaranteed to meet performance specifi cations from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating temperature range are assured by design, characterization and correlation with statistical process controls. The LT3475I and LT3475I-1 are guaranteed to meet performance specifi ...
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... LT3475/LT3475 TYPICAL PERFOR A CE CHARACTERISTICS LED Current vs V ADJ 1. 25°C A 1.25 1.00 0.75 0.50 0. 0.25 0.5 0.75 1 1.25 V (V) ADJ 3475 G01 Switch Current Limit vs Duty Cycle 3.0 TYPICAL 2.5 2.0 MINIMUM 1.5 1.0 0 25° DUTY CYCLE (%) 3475 G04 Oscillator Frequency vs Temperature 700 R = 24.3kΩ T 650 600 ...
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... LT3475/LT3475-1 Open-Circuit Output Voltage and Input Current 25°C A INPUT CURRENT 45 LT3475 LT3475 30 25 LT3475-1 20 OUTPUT VOLTAGE 15 LT3475 (V) IN 3475 G11 Minimum Input Voltage, Two Series Connected 1.5A White LEDs 25° ...
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... SHDN (Pin 16): The SHDN pin is used to shut down the switching regulator and the internal bias circuits. The 2.6V switching threshold can function as an accurate undervoltage lockout. Pull below 0.3V to shut down the LT3475/LT3475-1. Pull above 2.6V to enable the LT3475/ LT3475-1. Tie the SHDN function is unused. IN REF (Pin 17): The REF pin is the buffered output of the internal reference ...
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... Operation can be best understood by referring to the Block Diagram. If the SHDN pin is tied to ground, the LT3475 is shut down and draws minimal current from the input source tied the SHDN pin exceeds 1V, the internal bias ...
Page 8
... APPLICATIONS INFORMATION Open Circuit Protection The LT3475 has internal open-circuit protection. If the LED is absent or is open circuit, the LT3475 clamps the voltage on the LED pin at 14V. The switching regulator then oper- ates at a very low frequency to limit the input current. The LT3475-1 has no internal open circuit protection ...
Page 9
... Another consideration is the maximum duty cycle. In certain applications, the converter needs to operate at a high duty cycle in order to work at the lowest input voltage possible. The LT3475 has a fi xed oscillator off time and a variable on time result, the maximum duty cycle increases as the switching frequency is decreased. ...
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... LT3475/LT3475-1 APPLICATIONS INFORMATION current have signifi cantly increased. Exceeding V is safe if the external components have adequate ratings to handle the peak conditions and if the peak inductor current does not exceed 3.2A. A saturating inductor may further reduce performance. V OUT 500mV/DIV (AC COUPLED 1A/DIV ...
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... The input ca- pacitor is required to reduce the resulting voltage ripple at the LT3475 input and to force this switching current into a tight local loop, minimizing EMI. The input capacitor must have low impedance at the switching frequency to do this effectively, and it must have an adequate ripple current rat- ing ...
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... C(RMS) L The low ESR and small size of ceramic capacitors make them the preferred type for LT3475 applications. Not all ceramic capacitors are the same, however. Many of the higher value capacitors use poor dielectrics with high temperature and voltage coeffi cients. In particular Y5V and Z5U types lose a large fraction of their capacitance with applied voltage and at temperature extremes ...
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... The boost circuit also limits the minimum input voltage for proper start up. If the input voltage ramps slowly, or the LT3475 turns on when the output is already in regulation, the boost capacitor may not be fully charged. Because the boost capacitor charges ...
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... PWM 100Hz TO 10kHz pin by tying a low on resistance ADJ RATIO MAX ) as follows: MIN = I RATIO REF R1 LT3475 V ADJ GND R2 3475 F07 DIM V PWM C LT3475 3.3nF LED GND 3475 F08 Figure 8. Dimming Using PWM Signal ) can be ) and the pin, C pin for C 10k 0.1μF 3475fb ...
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... APPLICATIONS INFORMATION LT3475 to maintain diode current regulation with PWM pulse widths as short as 7.5 switching cycles (12.5μs for f = 600kHz). Maximum PWM period is determined by SW the system and is unlikely to be longer than 12ms. Using PWM periods shorter than 100μs is not recommended. The maximum PWM dimming ratio (PWM ...
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... 0.1 μ F REF ADJ1 ADJ2 GND 4.7 μ F 50V V SHDN IN BOOST1 BOOST2 C2 0.22 μ F 0.22 μ LT3475 6.3V 10 μ H SW1 SW2 D1 OUT1 OUT2 LED1 LED2 PWM1 PWM2 REF T 10k 3.3nF V V ADJ1 ADJ2 GND ...
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... IN BOOST1 BOOST2 C2 0.22 μ F 0.22 μ F LT3475 10V SW1 SW2 D1 OUT1 OUT2 LED1 LED2 REF ADJ1 ADJ2 GND LT3475/LT3475 μ 2.2 μ 6.3V C7 0.1 μ LED LED 1 24.3k CURRENT f = 600kHz SW 3475 TA04 10V 15 μ 2.2 μ F 10V LED ...
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... F 6.3V 0.1 μ F 1.5A LED LED 1 CURRENT D1, D2: B240A D3, D4: MMSD4148T1 C1 TO C5: X5R OR X7R 18 Dual Step-Down 1.5A Red LED Driver C1 4.7 μ 35V V SHDN IN BOOST1 BOOST2 C2 0.22 μ F 0.22 μ F LT3475 35V SW1 SW2 D1 OUT1 OUT2 LED1 LED2 REF ADJ1 ADJ2 GND D4 ...
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... BSC 0.195 – 0.30 (.0077 – .0118) 4. RECOMMENDED MINIMUM PCB METAL SIZE FOR EXPOSED PAD ATTACHMENT MILLIMETERS (INCHES) *DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.150mm (.006") PER SIDE LT3475/LT3475-1 6.40 – 6.60* (.252 – .260) 3.86 (.152 6.40 2.74 (.252) ( ...
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... D2, D3: MMSD4148 D5, D6: B240A D7, D8: 22V ZENER DIODE R1, R2: USE 0.5W RESISTOR OF TWO 2k 0.25W RESISTORS IN PARALLEL Q1, Q2: MMBT3904 C1 TO C5: X5R or X7R *DERATE LED CURRENT AT ELEVATED AMBIENT TEMPERATURES TO MAINTAIN LT3475-1 JUNCTION TEMPERATURE BELOW 125 °C. RELATED PARTS PART NUMBER DESCRIPTION LT1618 Constant-Current, 1.4MHz, 1.5A Boost ...