Linear Technology has introduced two 40V, 4.5A DC/DC converters, the LT3478 and LT3478-1, which drive high current LEDs at a constant current. Its 2.8V to 36V voltage input range is suitable for a wide range of applications including automotive, industrial and architectural lighting. In boost mode, the LT3478/-1 can drive up to six 700mA LEDs in series with a single 12V input, making the device ideal for backlighting applications in automotive displays. The LT3478-1 uses an internal current-sense resistor that limits the output current to 1A, while the LT3478 uses an external sense resistor to extend the LED's maximum current to 4.5A. Both devices are available in a thermally enhanced TSSOP-16E package with efficiencies as high as 90% in boost mode.
Featuring TrueColor PWM dimming, these devices provide constant LED color over a dimming range of up to 3000:1, and their fixed frequency, current mode architecture keeps the device stable over a wide range of supply and output voltages. The frequency adjustment pins of these devices allow the user to program from 200kHz to 2.25MHz, optimizing efficiency and minimizing component size.
The LT3478/-1 senses the output current at the high voltage side of the LED for buck, buck-boost, and boost configuration. One of the two CNTRL pins can be used to program the maximum current of the LED, and the other can be used to program the maximum current of the LED that decreases with increasing temperature, thereby maximizing LED usage and improving overall reliability. . Other features include inrush current protection, LED open circuit protection, and programmable soft start.
Both the LT3478EFE and LT3478EFE-1 are available from stock in a thermally enhanced 16-lead TSSOP-16E package. Both versions start at $3.60 each. The "I" grade versions of the extended temperature range, the LT3478IFE and LT3478IFE-1, are also available from stock. Buy in 1,000-piece quantities starting at $4.32 each.
Summary of LT3478 and LT3478-1 performance:
* True Color PWM dimming provides constant LED color over a dimming range of up to 3000:1
* Wide input voltage range: 2.8V to 36V
* 4.5A, 60mΩ, 42V internal switch
* Drive LEDs in boost, buck-boost or buck mode
* Integrated resistors for inductor and LED current sensing
* Programming LED current: 100mA to 1050mA (LT3478-1), (10mV to 105mV) / RSENSE (LT3478)
* Programming LED current decreases with increasing temperature
* Separate inductor power input
* Surge current protection
* Programmable soft start
Source: Electronic System Design
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