onsemi NCP121AMX173TCG

Overview

NCP121AMX173TCG from onsemi is a fixed-output, high-accuracy, very low dropout (VLDO) linear voltage regulator with NMOS pass transistor and dual-rail operation (VIN and VBIAS). It delivers 150 mA output at 1.73 V with ±1.0% accuracy over line/load/temperature, 75 mV max dropout at full load, and operates from 0.8 V to 5.5 V input while requiring ≥2.4 V bias supply. It is designed for noise-sensitive, space-constrained portable applications such as smartphone core logic or camera sensor power rails.

For engineers reviewing the NCP121AMX173TCG datasheet, pinout, applications, or equivalent options, key selection criteria include its ultra-low dropout under battery-sag conditions, bias-rail independence enabling stable regulation when VIN drops below VOUT + VDO, active output discharge capability, and compatibility with 1 µF ceramic output capacitors in XDFN6 1.2 mm × 1.2 mm packaging.

Technical Context

The NCP121AMX173TCG uses an NMOS pass device powered by a dedicated VBIAS rail (2.4–5.5 V), decoupling control circuitry from input supply limitations - enabling stable regulation even when VIN falls near or below nominal VOUT. Its internal reference and error amplifier achieve ±1.0% total output accuracy across −40°C to +85°C.

It integrates EN-controlled startup with monotonic rise, thermal shutdown (160°C trip), current limiting (200–600 mA), and - uniquely for the "A" variant - active output discharge (R_DISCH = 150 Ω) during disable. PSRR reaches 70 dB (VIN→VOUT) and 80 dB (VBIAS→VOUT) at 1 kHz, supporting clean power for RF or precision analog blocks.

Key Specifications

Pinout & Package

XDFN6 package (Case 711AT): 1.2 mm × 1.2 mm × 0.4 mm body with exposed thermal pad. Requires soldering of thermal pad to ground plane for optimal thermal performance and electrical stability.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6210B173MR-G and RT9013-17GB, the NCP121AMX173TCG provides superior accuracy (±1.0% vs. ±2%), lower dropout (75 mV vs. ≥120 mV), and unique VBIAS-enabled operation - making it the only option capable of sustaining 1.73 V regulation during deep battery discharge or noisy input conditions.

Availability

NCP121AMX173TCG is available at Aetrix Electronics and suitable for smartphone core power, camera sensor analog supplies, tablet SoC I/O domains, DVR memory interfaces, and other applications requiring stable component supply with tight voltage tolerance and ultra-low noise.

Supply support for NCP121AMX173TCG 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 NCP121AMX173TCG belongs to onsemi's high-accuracy, dual-rail VLDO family - engineered specifically for battery-powered portable electronics demanding ultra-low dropout, low noise, and robust operation under dynamic input and load conditions.

FAQ

What is the exact output voltage and accuracy of the NCP121AMX173TCG?

The NCP121AMX173TCG delivers a fixed 1.73 V output with ±1.0% accuracy over line, load, and temperature (−40°C to +85°C), and ±0.2% at 25°C. This is confirmed in the Electrical Characteristics table of the official datasheet (Rev. 1, October 2019), where VOUT accuracy is explicitly specified for the "AMX173" variant. The marking code "6" on the device corresponds to 1.73 V per the Ordering Information table.

Does the NCP121AMX173TCG support active output discharge, and how is it implemented?

Yes, the NCP121AMX173TCG supports active output discharge - a feature exclusive to the "A" variant (NCP121A). When the EN pin is driven low, an internal 150 Ω pull-down resistor connects OUT to GND, discharging the output capacitor rapidly. This behavior is documented in Figure 2 (block diagram footnote), the PIN FUNCTION DESCRIPTION, and the ELECTRICAL CHARACTERISTICS table (R_DISCH = 150 Ω).

What are the minimum required input and bias voltages for the NCP121AMX173TCG to regulate properly?

To maintain regulation, the NCP121AMX173TCG requires VIN ≥ VOUT + VDO = 1.73 V + 0.075 V = 1.805 V (max dropout at 150 mA), and VBIAS ≥ (VOUT + 1.35 V) = 3.08 V (per Electrical Characteristics table). The absolute minimum VBIAS is 2.4 V, but operation below 3.08 V may reduce PSRR or increase dropout. Both rails must remain within their respective absolute maximum ratings (−0.3 V to 6 V).

Can the NCP121AMX173TCG operate with only a single input rail, or is a separate VBIAS supply mandatory?

A separate VBIAS supply is mandatory for normal operation. The NCP121AMX173TCG's internal control circuitry - including reference, error amplifier, and bias generators - is powered exclusively from the BIAS pin. If VBIAS is omitted or shorted to GND, the device will not regulate, regardless of VIN level. The datasheet explicitly states that VBIAS must be ≥2.4 V and is monitored by an internal UVLO circuit.

What package type and thermal requirements apply to the NCP121AMX173TCG?

The NCP121AMX173TCG uses the XDFN6 package (Case 711AT): 1.2 mm × 1.2 mm × 0.4 mm with an exposed thermal pad. The datasheet specifies R_JA = 170 °C/W and mandates soldering the thermal pad to the PCB ground plane to meet thermal performance targets. Failure to connect the pad increases junction temperature risk, potentially triggering thermal shutdown at 150 mA continuous load.