Monolithic Power Systems Inc. MP171GJ-Z

Overview

MP171GJ-Z from Monolithic Power Systems is a 700 V primary-side constant-voltage (CV) offline regulator with integrated MOSFET, supporting buck/boost/buck-boost/flyback topologies in non-isolated AC/DC conversion. It delivers up to 60 mA output current in CCM, achieves <30 mW no-load power consumption, and operates across -40°C to +125°C junction temperature. It targets low-power standby supplies in home appliances and white goods.

For engineers reviewing the MP171GJ-Z datasheet, MP171GJ-Z pinout, MP171GJ-Z application, or MP171GJ-Z equivalent, this page provides verified technical context, validated pin functions, topology-specific design meaning, and real-world protection behavior - all derived from Monolithic Power's official MP171 Rev. 1.01 documentation.

Technical Context

The MP171GJ-Z implements green-mode operation via simultaneous frequency foldback and peak current compression: switching frequency and peak current both decrease under light load to maintain high efficiency down to no-load conditions. Its internal error amplifier samples FB voltage 6 µs after MOSFET turn-off and regulates against a 2.55 V reference.

It uses primary-side CV control without optocoupler feedback, relying on a sampling capacitor (C3) to hold output voltage for regulation. Protection logic includes auto-restart OLP (175 ms delay), SCP (300 mA threshold), thermal shutdown (150°C trip, 120°C recovery), and open-loop detection (<0.5 V FB).

Key Specifications

Pinout & Package

MP171GJ-Z is housed in a TSOT23-5 package (0.95 mm pitch, 2.8 × 2.9 mm footprint), optimized for compact offline regulators. Exposed DRAIN pad improves thermal dissipation in high-voltage switching applications.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar primary-side offline regulator applications.

Compared with MP171GJ-Z, MP171A-GJ-Z offers tighter regulation and extended lifecycle support, while LNK304DG-TL trades efficiency for higher power capability - making MP171GJ-Z suitable only for legacy repair or cost-sensitive replacements where its 30 mW no-load performance remains critical.

Availability

MP171GJ-Z is available at Aetrix Electronics and suitable for home appliance standby supplies, white goods control logic power, and consumer electronics auxiliary rails requiring stable component supply and legacy design continuity.

Supply support for MP171GJ-Z 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

Monolithic Power Systems (MPS) is a fabless semiconductor company specializing in high-performance analog and power ICs, with design centers in the US, China, and Taiwan.

The MP171 product line delivers primary-side offline regulators targeting cost-sensitive, low-power AC/DC conversion in consumer and industrial applications - emphasizing integration, efficiency, and protection robustness without optocouplers.

FAQ

What is the maximum output power achievable with MP171GJ-Z?

The MP171GJ-Z delivers up to 2 W output power in continuous conduction mode, limited by its 105 mA typical peak current and 700 V MOSFET. At 5 V output, this supports ≤60 mA load current; actual power depends on topology, input voltage, and thermal design - exceeding 2 W risks thermal shutdown due to 1 W TSOT23-5 package power dissipation limit.

Can MP171GJ-Z operate in flyback topology with isolation?

Yes - MP171GJ-Z supports flyback topology with isolation via an external transformer, though it uses indirect feedback (sampling capacitor on secondary side). The IC itself remains non-isolated; isolation is achieved by transformer coupling, not internal architecture. Flyback operation requires careful selection of turns ratio and snubber components to manage reflected voltage spikes within the 700 V DRAIN rating.

Why does MP171GJ-Z require a dummy load?

A minimum 3 mA dummy load ensures sufficient inductor energy to charge the sampling capacitor (C3) during each switching cycle, enabling accurate output voltage detection. Without it, light-load regulation degrades because C3 cannot maintain adequate voltage hold between cycles - especially critical in buck and buck-boost configurations where feedback relies on capacitor sampling.

How does the frequency foldback mechanism improve efficiency?

Frequency foldback reduces switching frequency proportionally with decreasing load, lowering switching losses (proportional to f_SW). Combined with peak current compression, it minimizes both conduction and switching losses at light loads - achieving <30 mW no-load consumption. This dual-foldback behavior is implemented in hardware and requires no external programming.

Is MP171GJ-Z RoHS compliant and lead-free?

Yes - MP171GJ-Z is fully RoHS-compliant, lead-free, and halogen-free per MPS quality assurance standards. It meets JEDEC J-STD-020 moisture sensitivity level 1 (MSL-1) and is qualified for reflow soldering at peak temperatures up to 260°C, consistent with TSOT23-5 package specifications.

What happens during open-loop protection activation?

When FB voltage drops below 0.5 V (indicating feedback loss or severe overload), MP171GJ-Z stops switching immediately and enters auto-restart mode. The VCC capacitor discharges via a 16 µA internal current source until VCC falls below VCC_pro (2.5 V), then the internal HV regulator recharges VCC to restart - repeating every ~1.2 seconds until fault clearance.

Does MP171GJ-Z support synchronous rectification?

No - MP171GJ-Z does not drive external synchronous rectifiers. It is designed for use with standard silicon or Schottky freewheeling diodes (e.g., SRGC10JH). Synchronous rectification would require additional gate-drive signals and timing control not provided by this IC's pinout or internal architecture.