500 mA adjustable LDO — PSRR and dropout drive the rail decision
The ADP125ACPZ-R7 is an adjustable positive-output LDO from Analog Devices, delivering up to 500 mA with a maximum dropout of 0.23 V at full load. PSRR is specified at 60 dB across the 10 kHz to 100 kHz band — this is the frequency range where typical buck converter switching noise lives. A 60 dB rejection means the ripple at the output is 1,000× lower than the input ripple at those frequencies, which matters for ADC reference rails, VCO supplies, or any analog front-end where switching noise couples into the signal chain.
Quiescent current and thermal envelope
Quiescent current is 105 µA typical, with a maximum supply current of 280 µA. For always-on rails in battery-powered or energy-harvesting designs, this Iq sits below the self-discharge rate of a small lithium cell — the regulator's own draw does not dominate the standby budget. Without the pad soldered to a copper plane, the junction-to-ambient thermal resistance rises and the output current must be derated above 85°C ambient. Protection features include over-current, over-temperature, and under-voltage lockout (UVLO) — the UVLO threshold prevents the pass FET from operating in the linear region during input brownout, which would otherwise dissipate excessive power in the die.
The 8-LFCSP footprint is shared with other members of the ADP125 family, so a pin-compatible drop-in exists if the output voltage or package variant needs to change.