Microchip Technology MIC4684-3.3BM

Overview

MIC4684-3.3BM from Micrel, Inc. is a fixed-output 3.3V, 2A continuous current synchronous buck regulator in an 8-lead Power-SO-8 package, operating at 200kHz PWM with >85% efficiency across 4V–30V input range and featuring internal NPN power switch, bootstrap drive, and thermal shutdown. It delivers stable 3.3V/1.5A at 60°C ambient in standard configuration and supports feed-forward diode for low-headroom 5V-to-3.3V conversion.

For engineers reviewing the MIC4684-3.3BM datasheet, MIC4684-3.3BM pinout, MIC4684-3.3BM application, or MIC4684-3.3BM equivalent, key selection criteria include its fixed 3.3V output, SO-8 thermal performance (θJA = 75°C/W), enable-controlled shutdown (150µA quiescent), feedback reference voltage (1.235V), and compatibility with external Schottky diodes and 68µH inductors in compact PCB layouts.

Technical Context

The MIC4684-3.3BM implements voltage-mode PWM control using a 1.235V bandgap reference and 200kHz oscillator to regulate output via variable duty cycle. Its internal NPN switch is driven by a bootstrap capacitor (pin BS) that elevates gate drive above VIN, reducing saturation voltage to 0.59V and sustaining high efficiency without external heat sinking.

Safety is enforced through integrated frequency-foldback short-circuit protection (30–120kHz), over-current limiting (2.2A typical), and thermal shutdown at 160°C. The device operates across –40°C to +125°C junction temperature and tolerates 34V input transients, making it suitable for industrial and automotive power rails where reliability under voltage stress is critical.

Key Specifications

Pinout & Package

Package: 8-lead Power-SO-8 (SOP-8M) with exposed die-attach paddle thermally connected to pins 2, 6, and 7 (GND). Pins 2/6/7 share common ground return path optimized for low-inductance, high-current switching and thermal conduction to PCB ground plane (min. 6 cm² recommended).

Key Features

Applications

Equivalent & Alternatives

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

Compared with LM2678-3.3SD/NOPB and TPS54231DR, the MIC4684-3.3BM offers simpler implementation with integrated NPN switch and bootstrap drive in a proven SO-8 thermal package, delivering reliable 2A output at 200kHz with minimal external components - ideal for cost-sensitive, space-constrained industrial and automotive applications where 30V max input suffices.

Availability

MIC4684-3.3BM is available at Aetrix Electronics and suitable for industrial automation, automotive body electronics, and portable medical devices requiring stable component supply, long-term lifecycle support, and consistent parametric performance across temperature and input voltage ranges.

Supply support for MIC4684-3.3BM 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

Micrel, Inc. was a U.S.-based analog and mixed-signal semiconductor company founded in 1978 and acquired by Microchip Technology in 2015; known for high-performance power management, timing, and interface ICs.

The MIC4684-3.3BM belongs to Micrel's SuperSwitcher™ family of integrated buck regulators, designed specifically to replace bulky TO-220/TO-263 switching solutions with compact, thermally enhanced SO-8 packages for industrial and automotive power conversion.

FAQ

What is the maximum continuous output current of the MIC4684-3.3BM at 60°C ambient temperature?

The MIC4684-3.3BM delivers 2A continuous output current at 60°C ambient temperature when mounted on a PCB with adequate ground-plane heatsinking (minimum 6 cm² copper area connected to pins 2, 6, and 7). This rating assumes standard configuration with 68µH inductor and appropriate input/output capacitors - exceeding this current requires derating based on thermal measurements per the SOA curves in the datasheet.

Does the MIC4684-3.3BM require external feedback resistors to set the output voltage?

No, the MIC4684-3.3BM is a fixed-output variant with the 3.3V regulation internally configured; no external feedback resistors are needed. Unlike the adjustable MIC4684 versions (e.g., MIC4684BM), the -3.3BM integrates the voltage divider, simplifying layout and improving output accuracy and stability. The FB pin is not accessible for external adjustment on this part number.

Can the MIC4684-3.3BM operate from a 5V input to deliver 3.3V output efficiently?

Yes, the MIC4684-3.3BM supports 5V-to-3.3V conversion efficiently, especially when using the feed-forward diode configuration described in the datasheet. This technique reduces effective headroom requirement and maintains >85% efficiency at 1.5A output. Standard configuration achieves ~88% efficiency at 5V input, 3.3V/1.5A, 60°C ambient - confirmed by efficiency vs. load curves on page 5.

What protection features are built into the MIC4684-3.3BM?

The MIC4684-3.3BM includes over-current protection with frequency-foldback during short circuits, thermal shutdown at 160°C junction temperature, and input overvoltage tolerance up to 34V transient. It also features enable-controlled shutdown reducing quiescent current to 150µA. These protections operate autonomously without external components, ensuring robust operation in harsh environments where input transients or thermal overload may occur.

Is the MIC4684-3.3BM pin-compatible with other members of the MIC4684 family?

Yes, all MIC4684 variants - including MIC4684-3.3BM, MIC4684BM (adjustable), and MIC4684YM - share identical 8-lead Power-SO-8 (SOP-8M) pinout and mechanical footprint. This allows drop-in replacement between fixed and adjustable versions during design iteration or production, provided external circuitry (e.g., feedback resistors, feed-forward diode) is updated accordingly to match the selected variant's functionality.