Negative-rail LDO for precision analog supplies
The LT1964EDD#PBF is a single-output negative adjustable LDO from Analog Devices, delivering up to 200 mA with a maximum dropout voltage of 0.49 V at full load. The adjustable output range spans -1.22 V to -20 V, making it suitable for generating clean negative rails for op-amps, ADCs, and sensor bias circuits. Power-supply rejection is 54 dB at 120 Hz, which attenuates mains-frequency ripple by a factor of ~500 — relevant when the input comes from a rectified AC source or a switching pre-regulator. The part includes over-current, over-temperature, and reverse-polarity protection, reducing the need for external clamp diodes or foldback circuits on the negative rail.
Dropout and headroom at 200 mA
The 0.49 V maximum dropout at 200 mA means the input must be at least 0.49 V more negative than the desired output under full load. For a -5 V output, a -5.5 V input rail provides margin across temperature and load. The enable control feature allows the regulator to be shut down, pulling the output to a high-impedance state — useful for sequencing multiple rails or reducing standby current.