Diodes Incorporated AP2128K-4.2TRG1

Overview

AP2128K-4.2TRG1 from BCD Semiconductor is a fixed-output 4.2V, 300mA CMOS low-dropout regulator with 170mV dropout at full load, ±2% output voltage accuracy, and 60µV_rms output noise. It operates from 2.5V to 6V input, features active shutdown (0.1µA standby), soft-start (50µs), and thermal/overcurrent protection-designed for powering RF sections and precision analog rails in portable datacom and notebook systems.

For engineers reviewing the AP2128K-4.2TRG1 datasheet, AP2128K-4.2TRG1 pinout, AP2128K-4.2TRG1 application, or AP2128K-4.2TRG1 equivalent, key selection criteria include its ultra-low noise performance, SOT-23-5 footprint compatibility with ceramic capacitors ≥1µF, shutdown logic interface, and thermal behavior under sustained 300mA loads across -40°C to +85°C ambient.

Technical Context

The AP2128K-4.2TRG1 uses a PMOS pass transistor architecture enabling low dropout and high PSRR (68dB @ 1kHz). Its internal reference (0.8V) and feedback network are trimmed to deliver 4.2V ±2% over line, load, and temperature without external resistors.

Shutdown control is active-high (1.5–6V logic threshold), enabling fast turn-off and auto-discharge via integrated 60Ω MOSFET. The device integrates thermal shutdown (165°C trip, 30°C hysteresis) and short-circuit current limiting (50mA), with stable operation using only 1µF ceramic input/output capacitors.

Key Specifications

Pinout & Package

SOT-23-5 package: 2.82 × 2.65 × 1.30 mm, surface-mount, RoHS-compliant (G1 suffix), rated for -40°C to +85°C ambient operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with XC6219B422MR-G and RT9193-42GB, the AP2128K-4.2TRG1 delivers superior noise performance and integrated discharge functionality, making it optimal for RF and battery-monitoring applications where signal integrity and controlled power sequencing are essential.

Availability

AP2128K-4.2TRG1 is available at Aetrix Electronics and suitable for wireless baseband power, Li-ion battery monitoring, notebook USB-C PD interface, and industrial sensor node applications requiring stable component supply, long-term manufacturability, and RoHS/Green compliance.

Supply support for AP2128K-4.2TRG1 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 mixed-signal IC designer specializing in high-performance power management, LED drivers, and audio amplifiers for consumer, computing, and industrial markets.

The AP2128 series belongs to BCD's ultra-low-noise LDO product line, engineered specifically for noise-sensitive analog and RF subsystems in portable electronics where traditional bipolar LDOs introduce unacceptable ripple and thermal overhead.

FAQ

Can AP2128K-4.2TRG1 operate with input voltage below 4.2V?

Yes, but only down to VIN = VOUT + V_DROP. With 170mV typical dropout at 300mA, minimum functional input is 4.37V. At lighter loads, dropout decreases-for example, 100mV at 100mA allows operation down to 4.3V. Operation below 4.37V at full load causes output droop or dropout.

Is an external resistor divider required for AP2128K-4.2TRG1?

No. The "K-4.2" suffix denotes the fixed-output variant. Unlike the ADJ version, it contains internal feedback resistors trimmed to deliver 4.2V ±2% without external components. Pin 5 (ADJ/NC) is no-connect and must remain unconnected.

What is the maximum allowable power dissipation in SOT-23-5 package?

At T_A = 85°C, θ_JA = 250°C/W limits P_D to 0.62W (calculated as (150°C − 85°C)/250°C/W). For 4.2V output at 300mA with VIN = 5.5V, P_D = (5.5V − 4.2V) × 0.3A = 0.39W - within safe operating area. Derating is required above 85°C ambient.

Does AP2128K-4.2TRG1 require input/output capacitors?

Yes. The datasheet mandates ≥1µF ceramic capacitors on both VIN and VOUT for stability and transient response. Using smaller values risks oscillation or excessive output ripple; tantalum or electrolytic types are unnecessary and discouraged due to ESR-related instability risks.