LDO regulator has ultra-low noise, high PSRR, for sensitive RF applications

February 24, 2015 // By Graham Prophet
LT3042 is an ultralow noise, ultrahigh power supply ripple rejection (PSRR) low dropout voltage linear regulator. Its design features ultralow spot noise of only 2 nV/√Hz at 10 kHz and 0.8 µVRMS integrated output noise across a wide 10 Hz to 100 kHz bandwidth.

Low and high frequency PSRR performance are exceptional. Low frequency PSRR exceeds 90 dB out to 10 kHz and high frequency PSRR exceeds 75 dB out to 3 MHz, quieting noisy or high ripple input supplies. The LT3042 uses Linear Technology’s LDO architecture–a precision current source reference followed by a high performance unity gain buffer, resulting in virtually constant bandwidth, noise, PSRR and load regulation performance independent of output voltage. Tis architecture permits paralleling of multiple LT3042s to further decrease noise, increase output current and spread heat on a printed circuit board.

The LT3042 delivers up to 200 mA output current with a 350 mV dropout voltage at full load, across a 1.8V to 20V input voltage range. Output voltage range is 0V to 15V and output voltage tolerance is highly accurate at ±2% over line, load and temperature. The device’s wide input and output voltage ranges, high bandwidth, high PSRR and ultralow noise performance make it suitable for powering noise-sensitive applications such as PLLs, VCOs, mixers, LNAs, very low noise instrumentation, high speed/high precision data converters, medical applications such as imaging and diagnostics, precision power supplies and as a post regulator for switching supplies.

The LT3042 operates with a small, low cost, 4.7 µF ceramic output capacitor, optimising stability and transient response. A single resistor programs the external precision current limit (±10% over temperature). A single SET pin capacitor lowers output noise and provides reference soft-start functionality, preventing output voltage overshoot at turn on. The device’s internal protection circuitry includes reverse battery protection, reverse current protection, internal current limit with foldback and thermal limit with hysteresis. Other features include fast start-up capability (useful if large value SET pin capacitors are used) and a power-good flag with programmable threshold to indicate output voltage regulation.

The LT3042 is available in thermally enhanced 10-lead 3 x 3 mm DFN and 10-lead MSOP packages, both with a compact footprint. E- and I-grade versions