Diodes Incorporated AP2128K-ADJTRG1

Overview

AP2128K-ADJTRG1 from BCD Semiconductor is a 300mA adjustable-output CMOS low-dropout (LDO) regulator in SOT-23-5 package, delivering 0.8V–5.5V output with ±2% accuracy, 170mV dropout at 300mA (VOUT=3.3V), and 60µV_RMS output noise. It integrates shutdown control, soft-start (50µs), thermal protection, and auto-discharge (60Ω R_DS(ON)), targeting power-sensitive analog and digital subsystems in portable electronics.

For engineers reviewing the AP2128K-ADJTRG1 datasheet, AP2128K-ADJTRG1 pinout, AP2128K-ADJTRG1 application, or AP2128K-ADJTRG1 equivalent, key selection criteria include adjustable output range, ultra-low noise performance, CMOS-based low-quiescent-current operation (60µA typ), and compatibility with 1µF ceramic input/output capacitors.

Technical Context

The AP2128K-ADJTRG1 uses a PMOS pass transistor architecture enabling low dropout and high PSRR (68dB @ 1kHz). Its reference voltage is internally trimmed to 0.8V (±2.5%), and output is set externally via resistor divider on ADJ pin - enabling precise regulation across 0.8V–5.5V while maintaining ±2% total output accuracy over -40°C to +85°C.

It features active shutdown with logic-level control (V_SHDN < 0.4V = OFF), 0.1µA standby current, and integrated thermal shutdown (165°C, 30°C hysteresis). The internal soft-start limits inrush current, and the VOUT discharge path ensures rapid rail collapse during shutdown.

Key Specifications

Pinout & Package

SOT-23-5 package: 2.82mm × 2.65mm × 1.3mm body, 0.95mm lead pitch, RoHS-compliant green finish (G1 suffix).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1703T-3302E/MB and XC6219B332MR-G, AP2128K-ADJTRG1 uniquely combines adjustable output, integrated shutdown with auto-discharge, 300mA capability, and sub-70µV_RMS noise in a single SOT-23-5 footprint - making it optimal for compact, multi-rail, battery-constrained systems requiring rapid rail control and analog-grade cleanliness.

Availability

AP2128K-ADJTRG1 is available at Aetrix Electronics and suitable for portable audio, wireless sensor nodes, industrial analog signal chains, and battery-powered microcontroller subsystems requiring stable component supply with guaranteed long-term sourcing.

Supply support for AP2128K-ADJTRG1 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 and power management IC designer specializing in high-efficiency, low-noise, and automotive-qualified power solutions.

The AP2128 series belongs to BCD's high-speed, ultra-low-noise CMOS LDO product line, engineered specifically for battery-powered portable electronics where output cleanliness, efficiency, and small-footprint integration are critical.

FAQ

What is the minimum input voltage required for AP2128K-ADJTRG1 to regulate a 1.2V output?

The AP2128K-ADJTRG1 requires VIN ≥ VOUT + V_DROP. At 300mA load and VOUT=1.2V, typical dropout is 1200mV (1.2V), so minimum VIN is 2.4V. However, datasheet specifies absolute minimum VIN of 2.5V across all conditions - thus 2.5V is the guaranteed operational floor for 1.2V output regulation.

Can AP2128K-ADJTRG1 be used without the ADJ pin connected?

No - the ADJ pin is mandatory for adjustable operation. Leaving it floating causes undefined output voltage and potential instability. For fixed-output versions (e.g., AP2128K-3.3TRG1), the ADJ pin is internally tied and unused; but AP2128K-ADJTRG1 requires an external resistor divider (R1/R2) between VOUT, ADJ, and GND to set output voltage per VOUT = 0.8V × (1 + R1/R2).

Does AP2128K-ADJTRG1 require an output capacitor, and what type is recommended?

Yes - a minimum 1µF ceramic capacitor (X5R or X7R) is required on VOUT for stability, transient response, and PSRR performance. The datasheet confirms compatibility with low-ESR ceramics and explicitly states that tantalum or electrolytic capacitors are unnecessary. Larger values (e.g., 2.2µF) improve load-transient recovery but are not required.

How does the shutdown function affect the VOUT pin behavior?

When SHUTDOWN is pulled low (<0.4V), the AP2128K-ADJTRG1 disables the pass transistor and activates an internal 60Ω discharge MOSFET between VOUT and GND. This actively pulls VOUT to near ground within milliseconds, preventing floating or slow decay - critical for sequencing-sensitive systems and reducing leakage in powered-down subsystems.