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Home > Products > Integrated Circuits (ICs) > Power Management (PMIC) > Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

Diodes Incorporated AP2128K-3.9TRG1

Name: AP2128K-3.9TRG1
Brand: Diodes Incorporated
SKU: AP2128K-3.9TRG1
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: AP2128K-3.9TRG1

Manufacturer:: Diodes Incorporated

Category:: Voltage Regulators - Linear, Low Drop Out (LDO) Regulators

Package:: SC-74A, SOT-753

Datasheet:: AP2128K-3.9TRG1.pdf

Description:: IC REG LINEAR 3.9V 300MA SOT23-5

Quantity:: RFQ Add To RFQ list

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Inventory:2,160

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Product details

Overview

AP2128K-3.9TRG1 from BCD Semiconductor Manufacturing Limited is a fixed-output 3.9V, 300mA CMOS low-dropout regulator with 170mV dropout at full load, ±2% output voltage accuracy, and 60µV_rms output noise. It features active shutdown (0.1µA standby current), thermal protection, soft-start (50µs), and compatibility with 1µF ceramic input/output capacitors. It powers core logic rails in portable computing and datacom systems where ultra-low noise and fast transient response are critical.

For engineers reviewing the AP2128K-3.9TRG1 datasheet, AP2128K-3.9TRG1 pinout, AP2128K-3.9TRG1 application, or AP2128K-3.9TRG1 equivalent, key selection criteria include dropout performance at 3.9V output, PSRR above 68dB at 1kHz, thermal shutdown threshold (165°C), and SOT-23-5 footprint compatibility with space-constrained PCB layouts.

Technical Context

The AP2128K-3.9TRG1 implements a PMOS pass transistor architecture enabling low dropout and high PSRR. Its internal reference (0.8V) and error amplifier regulate output via feedback to VOUT, with no external resistor network required for the fixed 3.9V version.

Shutdown control is TTL-compatible (0–0.4V "low", 1.5–6V "high"), activating an internal 60Ω discharge MOSFET and reducing quiescent current to 0.1µA. Thermal protection triggers at 165°C with 30°C hysteresis, and short-circuit current is limited to 50mA.

Key Specifications

Parameter	Value and Actual Design Meaning
Output Voltage	Fixed 3.9V ±2% - ensures stable supply for 3.3V/3.6V-tolerant I/O or analog subsystems without external resistors.
Max Output Current	300mA continuous - supports single-core microcontrollers, USB PHYs, or sensor signal chains in portable devices.
Dropout Voltage	170mV @ 300mA - enables operation from 4.07V input, critical for battery-powered systems down to single-cell Li-ion (3.4–4.2V).
PSRR	68dB @ 1kHz - suppresses switching noise from adjacent DC/DC converters feeding the same board.
Output Noise	60µV_rms (10Hz–100kHz) - preserves SNR in ADC references or RF bias rails.
Quiescent Current	60µA typical - minimizes battery drain during sleep modes in always-on subsystems.
Shutdown Current	0.1µA - enables deep-sleep power gating for IoT edge nodes.

Pinout & Package

SOT-23-5 package: 2.95mm × 1.70mm × 1.30mm body, 0.95mm lead pitch, RoHS-compliant green finish (G1 suffix).

Pin/Terminal	Circuit Role	Design Meaning
VIN	Input voltage supply	Accepts 2.5–6V; must be decoupled with ≥1µF ceramic capacitor close to pin.
GND	Ground reference	Common return for input/output capacitors and load; connects to thermal pad for θ_JA=250°C/W.
VOUT	Regulated output	Delivers fixed 3.9V; requires ≥1µF ceramic output capacitor for stability and transient response.
SHUTDOWN	Enable/disable control	Active-high logic: <0.4V disables regulator and engages 60Ω VOUT discharge path.
NC	No connect	Pin 5 is unconnected in fixed-output variants (K-package); must be left floating or grounded per layout best practice.

Key Features

Feature	Design Value
Low-noise regulation	60µV_rms output noise enables clean power for precision ADCs and RF front-ends.
Fast soft-start	50µs ramp time prevents inrush current and output overshoot during power-up.
Ceramic capacitor compatible	Stable with 1µF C_IN/C_OUT - eliminates need for costly tantalum or electrolytic capacitors.
Thermal robustness	165°C shutdown with 30°C hysteresis prevents latch-up during sustained overload or poor heatsinking.
High PSRR at audio band	68dB rejection at 1kHz - mitigates noise coupling from audio codecs or Class-D amplifiers on shared PCBs.

Applications

Portable Datacom Module

Notebook System Management Unit

Use Scenario: Powering 10/100BASE-TX PHY and MAC controller in compact Ethernet dongles.

IC Role / Device Role / Timing Role: Primary 3.9V LDO supplying digital I/O and reference voltage for PHY transceivers.

Use Value: 68dB PSRR isolates PHY from switch-mode converter ripple, ensuring <10⁻¹² BER under EMI stress.

Use Scenario: Regulating auxiliary rail for embedded controller (EC) and keyboard controller in ultrabook designs.

IC Role / Device Role / Timing Role: Always-on 3.9V supply enabling instant wake-from-suspend and secure boot sequencing.

Use Value: 0.1µA shutdown current extends battery life during multi-day suspend-to-RAM states.

Motherboard Voltage Tracking

Industrial Sensor Node

Use Scenario: Generating matched 3.9V rail for DDR memory termination and PCIe clock buffers.

IC Role / Device Role / Timing Role: Low-noise tracking regulator synchronized to main 3.3V VDDQ domain.

Use Value: ±100 ppm/°C tempco ensures voltage tracking stays within ±15mV across –40°C to +85°C ambient.

Use Scenario: Powering low-power wideband RF transceiver (sub-GHz ISM band) in battery-operated environmental monitors.

IC Role / Device Role / Timing Role: Clean 3.9V supply for RF synthesizer VCO and LNA bias networks.

Use Value: 60µV_rms noise prevents phase noise degradation, maintaining >45dBc adjacent-channel rejection.

Equivalent & Alternatives

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

Alternative Part	Technical Difference	Application Difference	Selection Advice
Torex XC6206P392MR	Same 3.9V fixed output, 300mA rating, but higher dropout (250mV @ 300mA) and lower PSRR (60dB @ 1kHz).	Lacks shutdown pin; unsuitable for systems requiring dynamic power gating.	Select when board space allows larger input headroom and shutdown functionality is unnecessary.
Richtek RT9193-39GB	3.9V output, 500mA rating, 200mV dropout, but higher noise (120µV_rms) and no auto-discharge MOSFET.	Higher max current supports heavier loads but degrades SNR in RF-sensitive designs.	Prefer when load current exceeds 300mA and noise sensitivity is secondary to current capacity.

Compared with XC6206P392MR and RT9193-39GB, the AP2128K-3.9TRG1 uniquely balances ultra-low noise, integrated shutdown with discharge, and tight dropout-making it optimal for noise-critical, battery-gated applications where footprint and thermal performance are constrained.

Availability

AP2128K-3.9TRG1 is available at Aetrix Electronics and suitable for notebook computers, datacom modules, motherboard power domains, and industrial sensor nodes requiring stable component supply across extended temperature ranges (–40°C to +85°C).

Supply support for AP2128K-3.9TRG1 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 fabless analog IC designer specializing in high-performance power management and mixed-signal solutions for consumer, industrial, and communications markets.

The AP2128 series targets ultra-low-noise, high-PSRR LDO applications in portable electronics, emphasizing CMOS process advantages for low quiescent current and fast transient response in compact SOT-23-5 packaging.

FAQ

What is the minimum input voltage required for stable 3.9V output at 300mA?

The AP2128K-3.9TRG1 requires VIN ≥ 4.07V (3.9V + 170mV dropout) for full-load regulation. Below this, output voltage sags linearly with input; operation below 2.5V violates absolute maximum ratings and risks functional failure.

Can the SHUTDOWN pin be left unconnected in always-on applications?

No. The SHUTDOWN pin has an internal 3MΩ pull-down resistor but must be actively driven to ≥1.5V for normal operation. Leaving it floating risks intermittent enable/disable behavior due to noise coupling; tie directly to VIN or use a pull-up resistor to VIN.

Is an external bypass capacitor required on the VREF node?

No. The AP2128K-3.9TRG1 integrates the 0.8V reference and error amplifier; no external VREF capacitor is needed or supported. Only input (C_IN) and output (C_OUT) 1µF ceramic capacitors are required for stability and transient performance.

Does the 60Ω VOUT discharge MOSFET activate during normal operation?

No. The 60Ω discharge path activates only when SHUTDOWN is driven low (<0.4V). During normal operation, the MOSFET is fully off, eliminating leakage paths that could compromise output hold-up time or load isolation.

AP2128K-3.9TRG1 Specifications

Product attributes: Attribute value

Manufacturer:: Diodes Incorporated

Series:: -

Package/Case:: SC-74A, SOT-753

Packaging:: Tape & Reel (TR)

Product Status:: Active

Output Configuration:: Positive

Output Type:: Fixed

Number of Regulators:: 1

Voltage - Input (Max):: 6V

Voltage - Output (Min/Fixed):: 3.9V

Voltage - Output (Max):: -

Voltage Dropout (Max):: 0.3V @ 300mA

Current - Output:: 300mA

Current - Quiescent (Iq):: 90 µA

Current - Supply (Max):: -

PSRR:: 68dB ~ 54dB (100Hz ~ 10kHz)

Control Features:: Enable

Protection Features:: Over Current, Over Temperature

Operating Temperature:: -40°C ~ 85°C

Grade:: -

Qualification:: -

Mounting Type:: Surface Mount

Supplier Device Package:: SOT-23-5

AP2128K-3.9TRG1 FAQ

1.How can I place an order for AP2128K-3.9TRG1 through Aetrix?

Please submit a Request for Quotation (RFQ) for AP2128K-3.9TRG1 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for AP2128K-3.9TRG1 reliable?

The price and inventory of AP2128K-3.9TRG1 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for AP2128K-3.9TRG1 is usually 5 days.

3.What payment methods are accepted for AP2128K-3.9TRG1?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for AP2128K-3.9TRG1 transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for AP2128K-3.9TRG1?

AP2128K-3.9TRG1 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your AP2128K-3.9TRG1 order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for AP2128K-3.9TRG1?

For technical support, including AP2128K-3.9TRG1 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your AP2128K-3.9TRG1 requirements.

6.How does Aetrix verify that AP2128K-3.9TRG1 is sourced from the original manufacturer or authorized distributors?

All AP2128K-3.9TRG1 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that AP2128K-3.9TRG1 meets industry standards.

7.What is the process for return or replacement of AP2128K-3.9TRG1?

All AP2128K-3.9TRG1 units undergo pre-shipment inspection (PSI). If there is an issue with AP2128K-3.9TRG1, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The AP2128K-3.9TRG1 part is unused and in its original packaging.

Return procedure for AP2128K-3.9TRG1:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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