Bias generators with ultralow noise and ripple for sensitive circuits

September 17, 2015 // By Graham Prophet
LT3095 is a dual-channel IC delivering two very low noise, low ripple bias supplies from a single input. Each channel incorporates a monolithic step-up DC/DC converter post-regulated by an integrated ultralow noise and high PSRR (power supply rejection ratio) linear regulator.

The device delivers up to 50 mA of continuous output current at output voltages up to 20V with total ripple and noise below 100 µVP-P. It operates from a 3V to 20V input voltage range. The LT3095’s fixed-frequency, peak current-mode step-up DC/DC converters include an integrated 950 mA power switch, Schottky diode and internal frequency compensation. Switching frequency is programmable between 450 kHz and 2 MHz via a single resistor or synchronisable to an external clock, enabling the use of tiny external components. Combined with a compact 3 x 5mm QFN package, the LT3095 offers a simple, compact solution footprint with good efficiency for instrumentation amplifiers, RF and data conversion systems, and other low noise biasing applications.

The LT3095’s linear regulators employ Linear’s current-source reference architecture, providing benefits such as single-resistor output voltage setting capability and bandwidth, noise, PSRR and load regulation performance virtually independent of output voltage. Integrated output noise (in a 10 Hz to 100kHz bandwidth) is 4 µVRMS and PSRR exceeds 70 dB over the entire switching frequency range, resulting in total noise and ripple under 100 µVP-P. The linear regulator adjusts the step-up converter’s output voltage to 2V above the linear regulator’s output voltage, optimising power dissipation, transient response and PSRR performance. To enhance system reliability, the LT3095 offers short-circuit and thermal protection, as well as providing independent precision enable/UVLO thresholds for each channel. Micropower operation results from both EN pins being pulled low.

The LT3095’s symmetric pinout simplifies PCB design. The device is housed in a thermally enhanced, 3 x 5 mm QFN-24 package, in both industrial E- & I-grade with -40°C to 125°C temperature range, and military MP-grade versions operating from -55°C to 125°C. The E grade is priced at $2.95 (1,000).

Linear Technology;