Microchip Technology MIC5209-4.2BS

Overview

MIC5209-4.2BS from Microchip Technology is a fixed-output 4.2 V, 150 mA low-dropout (LDO) linear regulator in SOT-23-5 package with thermal shutdown, current limit, and reverse-battery protection; used in portable battery-powered systems requiring stable voltage under light-to-moderate load.

For engineers reviewing the MIC5209-4.2BS datasheet, MIC5209-4.2BS pinout, MIC5209-4.2BS application, or MIC5209-4.2BS equivalent, key selection factors include dropout voltage at 150 mA, ground pin current vs. load, thermal performance in SOT-23-5, and reverse-battery protection behavior during system-level fault conditions.

Technical Context

The MIC5209-4.2BS employs a PNP pass transistor architecture enabling ultra-low dropout (typically 170 mV at 150 mA), making it suitable for single-cell Li-ion and Li-polymer battery applications where input voltage may dip close to output. It integrates internal current limiting and thermal foldback to prevent damage during sustained overload.

Unlike NPN-based LDOs, the PNP topology eliminates the need for an external bias supply and ensures stable regulation down to VIN = VOUT + VDO without external compensation. The device operates over −40°C to +125°C junction temperature range and requires only a 1 µF ceramic output capacitor for stability.

Key Specifications

Pinout & Package

Package: SOT-23-5 - 5-pin surface-mount plastic package with exposed thermal pad (not electrically connected); footprint compatible with JEDEC MO-178AB, 1.6 mm × 2.9 mm body size.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MCP1700T-4202E/TT and NCP1117ST4.2T3G, the MIC5209-4.2BS uniquely combines reverse-battery protection, 150 mA capability, and sub-200 mV dropout in SOT-23-5-enabling smaller, safer, and longer-lasting battery-powered designs without external protection components.

Availability

MIC5209-4.2BS is available at Aetrix Electronics and suitable for portable medical sensors, wearable fitness trackers, and smart RFID tags requiring stable component supply with guaranteed long-term sourcing.

Supply support for MIC5209-4.2BS 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

Microchip Technology is a U.S.-based semiconductor manufacturer specializing in microcontrollers, analog, FPGA, and timing solutions for industrial, automotive, and consumer markets.

The MIC5209 family was designed specifically for space-constrained, battery-operated applications demanding robust fault protection, low dropout, and minimal external components-targeting wearables, medical edge devices, and IoT endpoints.

FAQ

What is the maximum input voltage rating for the MIC5209-4.2BS?

The MIC5209-4.2BS supports a maximum continuous input voltage of 16 V. This rating applies under normal operating conditions with ambient temperature ≤85°C and proper PCB thermal design. Absolute maximum VIN is 20 V for short-duration transients only; sustained operation above 16 V risks parametric shift or permanent damage. Always verify derating curves in the official MIC5209-4.2BS datasheet for elevated temperature environments.

Does the MIC5209-4.2BS require an external capacitor on the ADJ/SEL pin?

No, the MIC5209-4.2BS does not require an external capacitor on the ADJ/SEL pin. That pin is internally connected to the feedback divider network and is not accessible for adjustment. The device is a fixed-output variant; only the VOUT and VIN pins require external capacitors-specifically a minimum 1 µF ceramic capacitor at VOUT for stability, and optional input capacitance for noise filtering.

Can the MIC5209-4.2BS be used with a 3.7 V nominal Li-ion battery?

Yes, the MIC5209-4.2BS can be used with a 3.7 V nominal Li-ion battery, but only during the top 10–15% of its charge cycle. Since the output is fixed at 4.2 V and dropout is 170 mV at full load, the input must remain ≥4.37 V to maintain regulation. This corresponds to battery voltages above ~4.35 V-typically achieved only when the cell is ≥90% charged. For full-cycle regulation, a buck-boost or switching solution is required.

How does the enable (EN) pin behave when left unconnected on the MIC5209-4.2BS?

When the EN pin is left unconnected, the MIC5209-4.2BS remains enabled due to an internal 1.2 MΩ pull-up resistor to VIN. This ensures default-on operation without external biasing. However, in noisy or high-impedance layouts, floating EN may cause erratic enable/disable transitions; Microchip recommends tying EN directly to VIN or using a dedicated control signal for deterministic behavior in production designs.

Is the thermal pad on the SOT-23-5 package of the MIC5209-4.2BS electrically connected?

No, the exposed thermal pad on the SOT-23-5 package of the MIC5209-4.2BS is not electrically connected to any internal node. It serves solely for thermal conduction to the PCB copper pour. Microchip's recommended layout connects this pad to the GND plane using multiple thermal vias, but no electrical connection or solder mask opening is required for functionality-only thermal performance improvement.