600-mA negative LDO+ offers rail-to-rail operation

September 27, 2013 // By Graham Prophet
Linear Technology's LT3090, in the company's LDO+ family, is a 600mA low dropout negative linear regulator featuring low noise, rail-to-rail operation, precision programmable current limit and a bidirectional output current monitor.

The device is cable-drop-compensation capable, capable of parallel connection for higher current or PCB heat spreading and configurable as a floating 3-terminal regulator. The LT3090’s input voltage range is -1.5V to -36V. A single resistor programs the adjustable rail-to-rail output voltage from 0V to -32V and dropout voltage is 300 mV (typical at full load). The device features a trimmed, ±1% accurate 50 µA current source reference and provides ±2% output voltage tolerance over line, load and temperature. Output voltage regulation, bandwidth, transient response and output noise (18 µVrms over a 10 Hz to 100 kHz bandwidth) remain independent of output voltage due to the device’s unity-gain voltage follower architecture. The LT3090 is suitable for negative logic supplies, low noise instrumentation and RF supplies, rugged industrial supplies and for post-regulating switching supplies.

The LT3090 exhibits excellent stability with a wide range of output capacitors including small, low cost ceramic capacitors. It is stable with a minimum 4.7 µF output capacitor. A single resistor adjusts the precision programmable current limit. The device’s bipolar current monitor either sources or sinks a current proportional to output current, useful for system monitoring. The LT3090’s bidirectional shutdown capability allows the device to operate with either positive or negative logic levels. In addition, the LT3090’s accurate shutdown thresholds enable a programmable UVLO threshold for either the regulator’s input supply or a positive system supply voltage. Internal protection circuitry for the IC includes a precision current limit with foldback and thermal shutdown with hysteresis. In bipolar supply applications where the regulator’s load returns to a positive supply, the OUT pin can be pulled above GND up to 40V and will still allow the LT3090 to safely start up.

The LT3090 is available in a low profile (0.75 mm) 3 x 3mm 10-lead DFN and a 12-lead MSOP package, both with backside thermal pads. E- and I-grade operating junction temperature is -40°C to +125°C, H-grade is -40°C to