Low-noise regulation with 45-V 500-mA LDO

June 04, 2013 // By Paul Buckley
Linear Technology has introduced a high voltage, low noise, low dropout voltage linear regulator offering precision, programmable current limit and diagnostic capability.

The LT3055 delivers up to 500 mA output current with a 350 mV dropout voltage at full load. The LT3055 features 2 to 45V input voltage range, delivering adjustable output voltages from 0.6V to 40V. A single capacitor at the REF/BYP pin provides programmable low noise operation - only 25 µVRMS across a bandwidth of 10 Hz to 100 kHz, and also reference soft start functionality, preventing output voltage overshoot at turn-on. Output voltage tolerance is accurate at ±2% over line, load and temperature.

The LT3055 provides several diagnostic and safety functions. A resistor at the IMAX pin programs current limit, accurate to ±10% over the full temperature range. Also, a resistor at the IMIN pin programs a minimum output current detector, useful for identifying open-circuit conditions. Furthermore, a current monitor function sources current equal to 1/500th of output current, allowing the user to measure output current or calculate the device’s power dissipation. Logic fault pins assert low if the LT3055 is in current limit (FAULT2), is operating below its minimum output current (FAULT1) or is in thermal limit (both FAULT1 and FAULT2). PWRGD indicates output regulation. The TEMP pin indicates die temperature. Moreover, the LT3055’s internal protection circuitry includes reverse-battery protection, reverse-output protection, reverse-current protection, internal default current limiting and thermal limiting.

The LT3055 operates with a small, low cost, 3.3 µF ceramic output capacitor, optimising stability and transient response. This tiny external capacitor can be used without the addition of series resistance (ESR) as is common with many other regulators. The LT3055’s wide input and output voltage ranges, fast transient response, low quiescent current of 65 µA (operating) and under 1 µA (in shutdown) make it an excellent choice for active antenna supplies, industrial power supplies, battery-powered systems requiring optimum run time, and high reliability power supplies requiring diagnostic information and protection functions.
In thermally enhanced 16-lead 3 x 4 mm DFN and 16-lead MSOP packages,pricing starts at