Texas Instruments LP3985IM5-4.7

Overview

LP3985IM5-4.7 from National Semiconductor is a micropower, 150mA ultra-low-dropout CMOS voltage regulator optimized for battery-powered portable wireless systems. It delivers 4.7V output with ≤100mV dropout at 150mA load, 30µVrms output noise (10Hz–100kHz), and consumes only 100–165µA quiescent current across temperature. It serves as the primary power supply for RF transceivers and baseband ICs in CDMA/GSM handsets.

For engineers reviewing the LP3985IM5-4.7 datasheet, LP3985IM5-4.7 pinout, LP3985IM5-4.7 application, or LP3985IM5-4.7 equivalent, key selection criteria include low-noise regulation under light-to-moderate loads, fast 200µs turn-on time with internal bypass pre-charge, thermal shutdown protection, and compatibility with 1µF ceramic output capacitors in space-constrained SOT-23-5 layouts.

Technical Context

The LP3985IM5-4.7 employs a CMOS pass transistor architecture enabling ultra-low dropout and minimal ground current variation in dropout-critical for extending battery runtime in deep-discharge conditions. Its bandgap reference includes an internal 70µA pre-charge current source for the BYPASS pin, decoupling noise reduction from transient response speed.

Power supply rejection exceeds 50dB at 1kHz with VIN = VOUT + 0.2V and maintains high rejection down to input voltages as low as 4.9V-ensuring clean output even as Li-ion cells discharge from 4.2V to 3.4V. Thermal shutdown activates at 160°C with 20°C hysteresis, and short-circuit current limit is fixed at 600mA (steady-state).

Key Specifications

Pinout & Package

SOT-23-5 package (NS package MF05A), 2.9mm × 1.6mm footprint, 1.1mm max height. Compatible with standard reflow profiles; no moisture sensitivity level (MSL) restriction per datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar low-noise LDO regulator applications.

Compared with XC6206P472MR and AP2210K-4.7TRG1, the LP3985IM5-4.7 uniquely combines 30µVrms noise, 50dB PSRR, internal BYPASS pre-charge, and thermal shutdown in SOT-23-5-making it the only option qualified for RF PA bias in commercial CDMA/GSM handsets.

Availability

LP3985IM5-4.7 is available at Aetrix Electronics and suitable for CDMA handset RF bias, GSM transceiver core supply, portable media player audio codec, Bluetooth baseband processor, and low-power IoT sensor node applications requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for LP3985IM5-4.7 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

National Semiconductor was a U.S.-based analog semiconductor company acquired by Texas Instruments in 2011; its legacy LDO portfolio remains widely deployed in mobile and wireless infrastructure.

The LP3985 product line was designed specifically for space- and noise-constrained battery-powered wireless handsets, emphasizing micropower operation, ultra-low dropout, and ceramic-capacitor compatibility in sub-3mm² footprints.

FAQ

What is the maximum input voltage rating for LP3985IM5-4.7?

The absolute maximum input voltage for LP3985IM5-4.7 is 6.5V, but the recommended operating range is 2.5V to 6.0V per datasheet specifications. Exceeding 6.0V risks violating the 6.5V absolute maximum and may trigger overvoltage stress on internal CMOS structures. For reliable operation with Li-ion batteries, VIN should remain between 4.2V (fully charged) and 3.4V (end-of-discharge), well within the safe operating window.

Does LP3985IM5-4.7 require an external bypass capacitor to achieve its specified 30µVrms noise performance?

Yes-LP3985IM5-4.7 achieves its 30µVrms output noise specification only when a 0.01µF NPO or COG ceramic capacitor is connected between the BYPASS pin and GND. Without this capacitor, output noise rises significantly; the datasheet confirms noise increases to ~230nV/√Hz spectral density with CBYPASS = 0. The BYPASS pin connects directly to the bandgap reference node, and the capacitor provides critical high-frequency filtering without affecting transient response.

Can LP3985IM5-4.7 operate stably with a 0.82µF X7R ceramic output capacitor?

Yes-LP3985IM5-4.7 is specified to remain stable with output capacitance as low as 0.7µF (±30% tolerance), so a 0.82µF X7R capacitor falls within the validated range. The datasheet explicitly states minimum COUT = 0.7µF and recommends X7R dielectric for −40°C to +125°C operation. Ensure the capacitor's DC-bias derating does not drop effective capacitance below 0.7µF at 4.7V bias; 0603 or larger case sizes are preferred for minimal bias shift.

What is the thermal shutdown behavior of LP3985IM5-4.7 during sustained overload?

LP3985IM5-4.7 activates thermal shutdown at 160°C junction temperature and remains latched off until junction temperature drops by 20°C (hysteresis), i.e., to ≤140°C. During overload, it first limits output current to 600mA (steady-state short-circuit limit); if power dissipation continues, die temperature rises until shutdown triggers. Recovery is automatic upon cooling-no external reset is required. This protects both the LP3985IM5-4.7 and downstream circuitry during PCB-level thermal faults.

Is LP3985IM5-4.7 pin-compatible with other output voltage variants in the SOT-23-5 package?

Yes-LP3985IM5-4.7 shares identical pinout, footprint, and electrical interface with all other LP3985IM5-x.x variants (e.g., LP3985IM5-3.3, LP3985IM5-5.0). The SOT-23-5 package (MF05A) has standardized pin assignments: VIN (pin 1), GND (pin 2), VOUT (pin 5), VEN (pin 3), BYPASS (pin 4). This allows drop-in replacement across output voltages during design iteration or BOM rationalization without layout changes.