Negative rail, tight dropout, wideband PSRR
The ADP7183ACPZN1.0-R7 is a negative-output low-dropout linear regulator from Analog Devices, delivering a fixed -1V at up to 300 mA. It is designed for applications that need a clean negative rail derived from a -5.5V maximum input — think op-amp bipolar supplies, sensor bias, or RF front-end rails where switching regulator noise would corrupt the signal. The headline spec is the PSRR: 85 dB at 1 kHz, rolling off to 40 dB at 1 MHz. That means it attenuates 1 kHz ripple by a factor of ~18,000, and even at 1 MHz it still knocks down noise by a factor of 100. For a sensitive analog chain powered from a noisy -5V bus, this regulator does the cleaning without needing a post-filter LC stage.
Dropout and thermal budget for the board
Maximum dropout is 220 mV at the full 300 mA load. Running from a -5V rail, that leaves 3.78 V of headroom — plenty to stay in regulation even if the input sags. The 900 µA quiescent current is moderate; not a battery-saving figure, but fine for a permanently-powered industrial rail. The package is an 8-lead LFCSP (2x2 mm) with an exposed pad — the 8-UFDFN designation. That pad is the main thermal path. On a standard 2-layer board with a small copper pour under the pad, expect the junction-to-ambient thermal resistance to be around 60-70 °C/W. At 300 mA and 4 V drop (1.2 W dissipation), the junction will rise about 80 °C above ambient, so the 125 °C junction rating gives margin in a 40-50 °C enclosure but not a lot. A 4-layer board with thermal vias drops that significantly. The enable pin lets you sequence the negative rail on and off. Protection features include current limit and thermal overload — standard for this class, but the thermal shutdown threshold is set high enough that it won't nuisance-trip on brief load transients.
Active production, no lifecycle worry
It is ROHS3 compliant and suitable for new designs. The -R7 suffix indicates 7-inch reel tape-and-reel packaging, which is the standard for this package size.