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Demonstration circuit 2257A features the LTM8005 – a 38VIN, 38VOUT boost μModule® LED driver that can disconnect the output to protect against faults and provides spread spectrum switching to simplify emissions compliance. DC2257A is an LED driver with an input range for normal operation from 6V to 27V. OVLO becomes active for inputs above 29V and the maximum input voltage is 38V. The LED current is 1.2A and the base switching frequency is 350kHz. The efficiency is 92% when the input is 12V with a 35V LED load. 35V is the maximum LED voltage.
The demo circuit requires application of an external voltage to the PWM terminal for operation. The external voltage can be a DC level or an appropriate PWM dimming signal. Common frequencies for PWM dimming are 100Hz or higher. Analog dimming is achieved using the CTRL inputs.
DC2257A allows adjustments to output voltage, output current, input current, switching frequency, frequency modulation rate including disable, feedback loop compensation, EN/UVLO threshold, OVLO threshold, soft-start period, and fault latch-off or hiccup. In most cases, adjustment is made by modifying the appropriate resistor or capacitor component(s).
DC2257A provides outputs for input and output current monitoring and fault status for short and open LEDs.
The demo circuit is designed to be easily reconfigured to buck mode, buck-boost mode and SEPIC topologies. There are placeholders to mount optional LC input filter components.
The LTM8005 data sheet must be read in conjunction with this demo manual to properly use or modify DC2257A.