Microchip Technology MIC4681-3.3BM

Overview

MIC4681-3.3BM from Micrel is a fixed-output 3.3V, 200kHz voltage-mode buck regulator in an 8-lead SOP package, delivering up to 1.4A continuous output current over a 4V–30V input range with internal 2.1A current limiting and thermal shutdown-designed for GSM battery charging and compact high-efficiency DC/DC conversion.

For engineers reviewing the MIC4681-3.3BM datasheet, MIC4681-3.3BM pinout, MIC4681-3.3BM application, or MIC4681-3.3BM equivalent, key selection considerations include its fixed 3.3V output, integrated NPN switch, 1.23V feedback reference, shutdown current of ≤6µA at V_SHDN = V_IN, and thermal design requirements for power-SOP-8 ground-plane layout.

Technical Context

The MIC4681-3.3BM implements voltage-mode control using a 200kHz oscillator and a 1.23V bandgap reference to regulate output via duty-cycle adjustment; it features cycle-by-cycle current limiting and foldback during short-circuit conditions to reduce energy per cycle.

Its internal NPN switch drives external inductor-diode output stage, with feedback sensed at the FB pin referenced to 1.23V-requiring no external compensation due to internal frequency compensation optimized for fast transient response with standard 68µH inductors and 220µF output capacitors.

Key Specifications

Pinout & Package

Package: 8-lead SOP (M), also known as power-SOP-8, featuring exposed die-attach paddle connected to pins 5–8 (GND) for enhanced thermal dissipation (θ_JA = 63°C/W typical on 6 cm² ground plane).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MIC4681BM, the MIC4681-3.3BM reduces component count and improves production yield for fixed 3.3V systems; compared with LM2678-3.3, it offers smaller footprint and lower quiescent current but lower current headroom and input voltage range.

Availability

MIC4681-3.3BM is available at Aetrix Electronics and suitable for cellular phone battery chargers, industrial point-of-load regulators, and GSM pulse power supplies requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MIC4681-3.3BM 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 power IC manufacturer acquired by Microchip Technology in 2015; known for high-performance SuperSwitcher™ DC/DC regulators and precision analog products.

The MIC4681 family was designed specifically for high-efficiency, low-component-count buck conversion in space- and cost-constrained portable electronics-emphasizing thermal robustness, GSM pulse handling, and ease of layout with the power-SOP-8 package.

FAQ

What is the output voltage tolerance of the MIC4681-3.3BM?

The MIC4681-3.3BM delivers a fixed 3.3V output with ±2% tolerance over temperature and line/load conditions, as specified in the Electrical Characteristics table. This tolerance is guaranteed across the full –40°C to +125°C junction temperature range and 4V–30V input voltage range, making MIC4681-3.3BM suitable for applications demanding stable 3.3V rail integrity without external trimming.

Does the MIC4681-3.3BM require external feedback resistors?

No, the MIC4681-3.3BM does not require external feedback resistors. It is a factory-trimmed fixed-output variant with internal resistor divider setting the output to 3.3V. The FB pin is internally connected to the 1.23V reference and is not accessible for adjustment-unlike the adjustable MIC4681BM, which requires R1/R2 to set V_OUT. This simplifies layout and reduces BOM for dedicated 3.3V applications.

What is the maximum continuous output current for MIC4681-3.3BM at 3.3V output?

The MIC4681-3.3BM supports up to 1.4A continuous output current at 3.3V output when operating at 25°C ambient with proper PCB thermal design (e.g., ≥6 cm² ground plane connected to pins 5–8). Derating applies above 25°C or with higher input voltages-see Figure 7 (SOA plots) in the datasheet for precise current limits versus VIN and ambient temperature.

How does the MIC4681-3.3BM handle short-circuit conditions?

The MIC4681-3.3BM employs cycle-by-cycle current limiting with a minimum threshold of 2.2A and automatic frequency foldback during hard short circuits-reducing switching frequency from 200kHz to ~60kHz to limit power dissipation. Thermal shutdown activates at 160°C junction temperature as a secondary protection layer, ensuring robust fault recovery without latch-up or damage under sustained overload.

Can the MIC4681-3.3BM be used in a negative-output buck-boost configuration?

No, the MIC4681-3.3BM is not suitable for negative-output buck-boost configurations. Its internal NPN switch and ground-referenced FB architecture require the output to be positive relative to GND. While the adjustable MIC4681BM can be configured in inverting topologies with external component changes, the fixed-output MIC4681-3.3BM lacks the necessary pin access and internal topology flexibility-use MIC4681BM or purpose-built inverting regulators instead.