Ultralow noise low dropout regulator

Louise Smyth

Linear Technology has developed an ultralow noise, ultrahigh power supply ripple rejection (PSRR) low dropout voltage linear regulator.

The LT3045 is a higher output current version of the widely accepted 200mA LT3042 ultralow noise LDO, with ultralow spot noise of only 2nV/√Hz at 10kHz and 0.8μVRMS integrated output noise across a wide 10Hz to 100kHz bandwidth.

The low frequency PSRR exceeds 90dB out to 10kHz and high frequency PSRR exceeds 70dB out to 2.5MHz, reducing noisy or high ripple input supplies.

The wide input and output voltage ranges, high bandwidth, high PSRR and ultralow noise performance are aimed at 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 device uses Linear’s proprietary 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.

In addition, this architecture permits paralleling of multiple devices to further decrease noise, increase output current and spread heat on a printed circuit board.

The LT3045 delivers up to 500mA output current with a 260mV dropout voltage at full load, across a wide 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 LT3045 operates with a small, low cost, 10μF 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.

Moreover, 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 a large value SET pin capacitor is used) and a power good flag with programmable threshold to indicate output voltage regulation.

The LT3045 is available in thermally enhanced 10-lead 3mm x 3mm DFN (pin-compatible with the LT3042) and 12-lead MSOP packages, both with a compact footprint.

The E- and I-grade versions are available from stock with an operating junction temperature of –40°C to 125°C. A future high temperature H-grade version will be rated from –40°C to 150°C.