1.5A negative LDO+ with current limiting and monitoring

September 22, 2015 // By Graham Prophet
LT3091 is a 1.5A low dropout negative linear regulator the majors on low noise, rail-to-rail operation, precision programmable current limit and a bidirectional output current monitor.

The device is cable-drop compensation capable, can be paralleled for higher current or circuit board heat spreading, and is configurable as a 3-terminal floating regulator. The LT3091’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 has 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 LT3091 is suitable for negative logic supplies, low noise instrumentation and RF supplies, rugged industrial supplies and for post-regulating switching supplies.

LT3091 exhibits good stability with a wide range of output capacitors including small, low cost ceramic capacitors. It is stable with a minimum 10 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 LT3091’s bidirectional shutdown capability allows the device to operate with either positive or negative logic levels. LT3091’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 34V and will still allow the LT3091 to safely start up.

The LT3091 is available in a low profile (0.75mm) 3 x 4 mm 14-lead DFN and a 16-lead TSSOP package, both with backside thermal pads. Additionally, the device is available in the TO-220-7 and DD-Pak-7 power packages. Pricing starts at $2.87