Negative rail regulator for bipolar analog front-ends
The ADP7185ACPZN1.2-R7 is a negative-output low-dropout linear regulator from Analog Devices, delivering a fixed -1.2 V at up to 500 mA. In a dual-supply signal chain — op-amp rails, ADC reference drivers, or sensor bias — this part generates the negative rail from a -5.5 V max input without a switching inverter and its associated ripple. Its power-supply rejection ratio of 80 dB at 1 kHz, rolling off to 40 dB at 1 MHz, means high-frequency noise from the upstream rail is attenuated by a factor of 10,000 at low frequencies, preserving the noise floor of precision analog stages.
Dropout voltage and thermal budget
Maximum dropout is 360 mV at the full 500 mA load. That sets the minimum input-to-output differential: a -1.56 V input rail is the floor to maintain regulation at full current. Below that headroom the output falls out of regulation, so the upstream buck or LDO feeding this part must hold at least -1.56 V under load. Junction temperature range spans -40°C to 125°C, covering automotive under-hood and industrial motor-drive ambient conditions. The 2x2 mm 8-LFCSP exposed pad (UFDFN) package relies on the PCB copper pour under the pad for thermal dissipation — a 1-square-inch pour on a 2-layer board keeps the junction rise below 50°C at 500 mA with 1.5 V dropout.
Control and protection for sequenced rails
Over-current protection limits the output during a fault — the regulator folds back rather than latching off, so a transient short clears without a power cycle. Quiescent current is 900 µA typical, rising to 7 mA maximum under heavy load. In a battery-powered device where the negative rail is always on, that Iq draws about 22 mW from a -2.5 V input — a consideration for standby budgets.