Texas Instruments LP3985IM5-3.2

Overview

LP3985IM5-3.2 from National Semiconductor is a micropower, 150mA ultra-low-dropout CMOS voltage regulator optimized for battery-powered portable wireless systems. It delivers 3.2V output with ≤100mV dropout at full load, 30µVrms output noise (10Hz–100kHz), and consumes only 85–150µA quiescent current across temperature. It serves as the primary power supply for RF transceivers and baseband ICs in compact cellular handsets.

For engineers reviewing the LP3985IM5-3.2 datasheet, LP3985IM5-3.2 pinout, LP3985IM5-3.2 application, or LP3985IM5-3.2 equivalent, key selection criteria include low-noise performance in RF-sensitive signal chains, minimal PCB footprint (SOT-23-5), fast 200µs turn-on time for power sequencing, and stable operation with 1µF ceramic output capacitors.

Technical Context

The LP3985IM5-3.2 uses a CMOS pass transistor architecture to achieve ultra-low dropout and near-zero ground current increase in dropout-critical for extending battery runtime. Its bandgap reference includes an internal 70µA pre-charge current source for the BYPASS pin, enabling fast startup without degrading load transient response.

Power supply rejection exceeds 50dB at 1kHz under VIN = VOUT + 0.2V conditions and remains effective down to input voltages as low as 2.5V. Thermal shutdown (160°C) and short-circuit current limiting (600mA steady-state) are integrated for robust system-level protection.

Key Specifications

Pinout & Package

LP3985IM5-3.2 is housed in a RoHS-compliant SOT-23-5 package (NS package code MF05A), measuring 2.9mm × 1.6mm × 1.1mm, with gull-wing leads and standard JEDEC MO-178 footprint. This surface-mount package enables high-density layout in space-constrained handheld PCBs.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P322MR and AP2112K-3.2TRG1, the LP3985IM5-3.2 uniquely combines 30µVrms noise, BYPASS-enabled noise tuning, and guaranteed 150mA delivery in SOT-23-5-making it the only option qualified for RF signal-chain power in 3G handset designs.

Availability

LP3985IM5-3.2 is available at Aetrix Electronics and suitable for CDMA/GSM/WCDMA handset design, portable medical telemetry, and industrial IoT sensor nodes requiring stable component supply with full traceability and long-term lifecycle support.

Supply support for LP3985IM5-3.2 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, known for precision power management and data conversion ICs.

The LP3985IM5-3.2 belongs to National's micropower LDO family engineered specifically for space- and noise-constrained battery-operated wireless terminals, emphasizing ultra-low IQ, sub-100mV dropout, and RF-grade noise performance.

FAQ

What is the maximum input voltage rating for LP3985IM5-3.2?

The absolute maximum input voltage for LP3985IM5-3.2 is 6.5V, but the recommended operating range is 2.5V to 6.0V. Exceeding 6.5V risks permanent damage to the CMOS pass element. For reliable long-term operation in battery-powered systems, VIN should remain ≤6.0V even during surge events-designers should include clamping or overvoltage protection if upstream sources exceed this limit. The LP3985IM5-3.2 maintains regulation down to VIN = VOUT + 100mV, making it ideal for single-cell Li-ion applications.

Does LP3985IM5-3.2 require an external bypass capacitor to meet datasheet noise specifications?

Yes, the 30µVrms output noise specification for LP3985IM5-3.2 is measured with a 0.01µF NPO/COG ceramic capacitor connected between the BYPASS pin and GND. Omitting this capacitor increases output noise to approximately 230nV/√Hz spectral density-effectively doubling integrated RMS noise. The BYPASS capacitor does not affect load transient response, so designers can optimize its value (0.001–0.022µF) to balance noise reduction against startup time, as smaller values yield faster turn-on. The LP3985IM5-3.2 will operate without it but fails to achieve its rated low-noise performance.

Can LP3985IM5-3.2 be used with a 0.7µF output capacitor?

Yes, LP3985IM5-3.2 is stable with a minimum 0.7µF ceramic output capacitor, as specified in the Recommended Output Capacitor table. However, using exactly 0.7µF requires careful capacitor selection: X7R dielectric, ±30% tolerance, and ESR between 5mΩ and 500mΩ across −40°C to +125°C. At temperature extremes or under DC bias, capacitance may dip below 0.7µF-causing instability or overshoot. National recommends 1.0µF as the nominal value to ensure margin; the LP3985IM5-3.2's stability is validated only with capacitors meeting these exact ESR and bias requirements.

What is the function of the VEN pin on LP3985IM5-3.2, and what logic levels enable it?

The VEN pin on LP3985IM5-3.2 is an active-high digital enable input that controls regulator output state. It turns the device ON when pulled to ≥1.4V (VIH) and OFF when pulled to ≤0.4V (VIL). Input leakage is ±1nA, allowing direct connection to 1.8V or 2.8V microcontroller GPIOs without level-shifting. When unused, VEN must be tied to VIN to ensure continuous operation. The LP3985IM5-3.2 achieves full regulation within 200µs after VEN crosses VIH, making it suitable for rapid power cycling in TDMA-based communication protocols.

Is LP3985IM5-3.2 compatible with tantalum output capacitors?

LP3985IM5-3.2 is stable with high-quality tantalum output capacitors meeting the 0.7–1.0µF capacitance and 5–500mΩ ESR specifications-but ceramic is strongly preferred. Tantalum capacitors exhibit higher ESR (especially at −40°C, where ESR can double), increased cost, larger footprint, and risk of catastrophic failure under surge current. The LP3985IM5-3.2's design optimizations-including fast transient response and low-noise operation-are fully realized only with X7R/X5R ceramics. If tantalum must be used, verify manufacturer-specified surge current ratings and derate voltage by 50% to ensure reliability; the LP3985IM5-3.2 itself imposes no restriction beyond ESR and capacitance compliance.