onsemi NCP3985SN18T1G

Overview

NCP3985SN18T1G from onsemi is a 150 mA, 1.8 V fixed-output micropower low-noise LDO voltage regulator in TSOP-5 package, featuring 70 dB PSRR at 1 kHz, 20 µV_RMS output noise (with 100 nF C_noise), ultra-low dropout of 105 mV at 150 mA, and active discharge circuitry - designed for noise-sensitive analog power supplies in battery-powered portable devices.

For engineers reviewing the NCP3985SN18T1G datasheet, pinout, applications, or equivalent options, key selection criteria include its 1.8 V output accuracy (±2% over load/temperature), stable operation with 1 µF ceramic output capacitor, 1 µA max sleep-mode current, CE-controlled enable/disable functionality, and thermal shutdown protection at 150°C.

Technical Context

The NCP3985SN18T1G employs a BiCMOS process to combine bipolar low-noise performance with CMOS-level ground current efficiency. Its bandgap reference feeds an error amplifier driving a PMOS pass device, with dedicated C_noise pin providing direct access to the reference node for external noise filtering.

It integrates chip-enable logic with internal 5 MΩ pull-down resistor, active discharge transistor for rapid V_OUT discharge upon disable, current limit (200 mA min), and thermal shutdown with 20°C hysteresis - all optimized for stable, low-quiescent-power operation in space-constrained portable systems.

Key Specifications

Pinout & Package

TSOP-5 (Case 483), 3.00 × 1.50 × 0.95 mm, Pb-free, surface-mount package with exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LP3985IMX-1.8/NOPB and MCP1700T-1802E/TT, the NCP3985SN18T1G delivers superior noise performance (20 µV_RMS vs. ≥30 µV_RMS), higher PSRR, and integrated active discharge - making it the preferred choice for battery-powered systems requiring both ultra-low noise and controlled power sequencing.

Availability

NCP3985SN18T1G is available at Aetrix Electronics and suitable for cellular telephones, portable GPS receivers, noise-sensitive audio codecs, and low-power sensor hubs requiring stable component supply, long-term lifecycle support, and Pb-free compliance.

Supply support for NCP3985SN18T1G 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

onsemi (formerly ON Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensing, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The NCP3985SN18T1G belongs to onsemi's NCP3985 family of micropower LDOs, engineered specifically for battery-powered portable electronics demanding ultra-low noise, high PSRR, and minimal quiescent current without sacrificing transient response or stability.

FAQ

What is the maximum input voltage for the NCP3985SN18T1G?

The NCP3985SN18T1G supports an absolute maximum input voltage of 6 V. However, for reliable operation within recommended conditions, the input voltage must remain between 2.5 V and 5.5 V when regulating 1.8 V output - ensuring sufficient headroom for the 105 mV dropout while avoiding overstress of internal circuitry.

Does the NCP3985SN18T1G require an external capacitor on the Cnoise pin?

Yes, the NCP3985SN18T1G requires a capacitor (10 nF to 100 nF) connected between the C_noise pin and GND to achieve specified low-noise performance. Without this capacitor, output noise rises to 25 µV_RMS; using 100 nF reduces it to 20 µV_RMS, directly improving signal integrity in noise-critical analog stages.

How does the active discharge feature work in the NCP3985SN18T1G?

When the CE pin is driven low, the NCP3985SN18T1G activates an internal NMOS transistor between V_OUT and GND, rapidly discharging the output capacitor. This eliminates residual voltage that could cause unintended behavior in downstream circuitry and removes the need for external bleed resistors - a key advantage in space-constrained portable designs.

What is the thermal shutdown threshold of the NCP3985SN18T1G?

The NCP3985SN18T1G triggers thermal shutdown at a typical junction temperature of 150°C, with 20°C hysteresis. Once tripped, the device remains disabled until the die cools to approximately 130°C. This protects against catastrophic failure during sustained overload or poor PCB thermal design, but is not a substitute for proper heatsinking.

Can the NCP3985SN18T1G operate with a 1 µF ceramic output capacitor?

Yes, the NCP3985SN18T1G is explicitly characterized and guaranteed stable with a 1 µF ceramic output capacitor - no minimum ESR requirement. This simplifies design, reduces component count, and saves board space compared to LDOs needing larger or higher-ESR capacitors for stability.