4.7V fixed LDO — 150 mA, 0.1 V dropout
The LP3985IM5X-4.7/NOPB is a fixed-output linear regulator from Texas Instruments delivering 4.7 V at up to 150 mA. The 0.1 V maximum dropout at full load means the input rail needs to stay above 4.8 V to maintain regulation — a 5 V rail with 200 mV of ripple still has headroom.
PSRR profile and noise rejection
PSRR is specified at 50 dB at 1 kHz, dropping to 40 dB at 10 kHz. This means the regulator attenuates 1 kHz ripple by a factor of ~316, but at 10 kHz the attenuation drops to ~100. For an analog front-end sensitive to switching-regulator noise above a few kilohertz, additional post-filtering may be needed. Quiescent current is 150 µA typical, with a maximum supply current of 250 µA. The 150 µA Iq is low enough for always-on rails in battery-powered designs — a sensor node drawing 10 µA in sleep mode sees the regulator's own draw dominate the sleep budget.
Protection and temperature range
Built-in over-current, over-temperature, and short-circuit protection reduce the need for external supervisory components. The enable pin (active high) allows the regulator to be shut down externally, pulling the output to high-impedance and reducing the load on the input rail.
The 5-pin footprint with 0.95 mm pitch fits a two-layer board — the thermal pad is the tab on pin 5 (output), and the copper area under it sets the junction-to-ambient thermal resistance.