Low dropout (LDO) linear regulators have been widely used in noise-sensitive applications for decades. However, the latest precision sensors, high-speed and high-resolution data converters (ADCs and DACs), and frequency synthesizers (PLL/VCOs) continue to challenge traditional LDO regulators to produce ultra-low output noise and ultra-low output noise. With high power supply ripple rejection (PSRR), noise requirements become increasingly difficult to meet. For example, when powering a sensor, power supply noise can directly affect the accuracy of the measurement results. Switching regulators are often used in power distribution systems to achieve higher overall system efficiency. To build a low-noise power supply, LDO regulators typically post-regulate the output of a relatively noisy switching converter without the need for bulky output filter capacitors. The high-frequency PSRR performance of the LDO regulator becomes critical.

The LT3042, launched in 2015, is the industry's first linear regulator with only 0.8μVrms output noise and 79dBPSRR at 1MHz. Two similar devices, the LT3045 and LT3045-1, offer higher ratings and additional features. All these devices are positive LDO regulators. When the system has bipolar devices such as op amps or ADCs, a negative LDO regulator must be used in the polar power supply design. The LT3094 is the first negative LDO regulator with ultra-low output noise and ultra-high PSRR. Table 1 lists the key features of the LT3094 and related devices.

Typical applications

The LT3094 features a precision current source reference followed by a high performance output buffer. The negative output voltage is programmable with a -100µA precision current source flowing through a single resistor. This current-reference-based architecture provides a wide output voltage range (0V to -19.5V) and provides nearly constant output noise, PSRR, and load regulation regardless of the programmed output voltage. Figure 1 shows a typical application, and the demo board is shown in Figure 2. The overall solution size is only approximately 10mm×10mm.