1.2V fixed rail for noise-sensitive loads
The MCP1825T-1202E/ET is a 500 mA low-dropout regulator with a fixed 1.2 V output, in a TO-263-6 (D²Pak) package with an exposed thermal tab. It is part of Microchip's MCP1825 family of LDOs aimed at point-of-load regulation for mixed-signal and digital cores that need a clean 1.2 V rail. The 60 dB PSRR at 100 Hz means the regulator attenuates line-frequency ripple from a rectified mains supply by a factor of 1000 — a meaningful figure when the input comes from a flyback or half-bridge converter with 100/120 Hz ripple on the bulk capacitor.
Dropout and thermal budget at full load
At full load the power dissipated in the pass element is 175 mW (0.35 V × 0.5 A), which the D²Pak tab must sink to the board copper. The quiescent current is 220 µA typical — the regulator's own draw is low enough that a battery-powered sensor waking once a minute spends most of its energy on the load, not the LDO. The enable pin lets the system shut the regulator down entirely when the rail is not needed.
Active production and compliance
The junction temperature must stay within this range including self-heating from the dropout voltage times load current — the exposed tab on the D²Pak is the primary thermal path, and board copper area under the tab sets the effective thermal resistance.