Diodes Incorporated AP2128K-1.8TRG1

Overview

AP2128K-1.8TRG1 from BCD Semiconductor is a fixed-output 1.8 V, 300 mA CMOS low-dropout regulator with 170 mV dropout at 300 mA (V_OUT=3.3 V), ±2% output voltage accuracy, 60 µV_rms output noise, and integrated soft-start (50 µs) and thermal shutdown. It operates from 2.5 V to 6 V input and targets power-sensitive applications including notebook CPU core logic and motherboard I/O rails.

For engineers reviewing the AP2128K-1.8TRG1 datasheet, AP2128K-1.8TRG1 pinout, AP2128K-1.8TRG1 application, or AP2128K-1.8TRG1 equivalent, key selection criteria include dropout performance at 1.8 V output, PSRR (68 dB @ 1 kHz), standby current (0.1 µA), compatibility with 1 µF ceramic capacitors, and SOT-23-5 footprint constraints.

Technical Context

The AP2128K-1.8TRG1 uses a CMOS pass transistor architecture enabling ultra-low quiescent current (60 µA typical) and extremely low output noise (60 µV_rms). Its internal reference (0.8 V) and error amplifier regulate output via feedback from the fixed 1.8 V output node - no external resistors required.

It integrates active shutdown control with logic-level compatible enable input (V_SHDN "High" ≥1.5 V), auto-discharge MOSFET (R_DS(ON) = 60 Ω), over-temperature protection (165 °C trip, 30 °C hysteresis), and short-circuit current limiting (50 mA). The device supports stable operation with 1 µF input and output ceramic capacitors.

Key Specifications

Pinout & Package

SOT-23-5 package: 2.82 mm × 2.65 mm × 1.45 mm body, 0.95 mm lead pitch, gull-wing leads. RoHS-compliant, green (Pb-free) finish per G1 suffix.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6206P182MR and RT9193-18GB, the AP2128K-1.8TRG1 uniquely combines ultra-low noise (60 µV_rms), integrated discharge (60 Ω), and precise soft-start (50 µs) in a single SOT-23-5 package - making it optimal for noise-critical, space-constrained, and sequenced-power applications.

Availability

AP2128K-1.8TRG1 is available at Aetrix Electronics and suitable for notebook computers, motherboard I/O rails, mobile baseband power, and industrial sensor hubs requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant green packaging.

Supply support for AP2128K-1.8TRG1 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

BCD Semiconductor Manufacturing Limited is a Shanghai-based analog IC design and wafer fabrication company specializing in power management, LED drivers, and mixed-signal solutions for consumer, computing, and industrial markets.

The AP2128 series belongs to BCD's high-performance LDO product line, engineered specifically for battery-powered devices demanding ultra-low noise, low quiescent current, and compact packaging - with emphasis on notebook, datacom, and portable electronics applications.

FAQ

What is the minimum input voltage required for AP2128K-1.8TRG1 to maintain regulation at full 300 mA load?

The AP2128K-1.8TRG1 requires VIN ≥ 2.5 V to operate, but to sustain 1.8 V output at 300 mA, VIN must exceed VOUT + VDROP. Per datasheet Table 7, dropout is 600–700 mV at 300 mA, so minimum functional VIN is 2.4–2.5 V. For reliable margin, use VIN ≥ 2.6 V under worst-case conditions.

Can AP2128K-1.8TRG1 be used with ceramic output capacitors smaller than 1 µF?

No - the datasheet specifies stability with ≥1 µF ceramic capacitors (X5R/X7R) on both input and output. Using smaller values risks oscillation due to insufficient phase margin; 1 µF is the validated minimum for guaranteed stability across temperature and load.

Does the NC pin (Pin 5) require any PCB layout treatment?

Pin 5 is internally unconnected in the fixed-output AP2128K-1.8TRG1. It should be left floating or optionally tied to GND for mechanical reinforcement and EMI reduction - but must never be connected to VIN, VOUT, or a signal net, as it has no internal function.

How does the auto-discharge feature behave during shutdown?

When SHUTDOWN is pulled low (≤0.4 V), the internal 60 Ω discharge MOSFET connects VOUT to GND, actively bleeding stored charge from the output capacitor. This reduces VOUT to <100 mV within ~1 ms (τ = R×C = 60 Ω × 1 µF = 60 µs), preventing unintended wake-up or latch-up in downstream logic.