Monolithic Power Systems Inc. MP174GJ-Z

Overview

MP174GJ-Z from Monolithic Power Systems is a 700V primary-side constant-voltage (CV) off-line regulator with integrated MOSFET, supporting Buck, Buck-Boost, Boost, and Flyback topologies. It delivers up to 400mA output current in CCM mode, achieves <30mW no-load power consumption, and operates in green-mode with frequency foldback and peak-current compression for high light-load efficiency. It targets non-isolated low-power AC/DC conversion in home appliance standby supplies.

For engineers reviewing the MP174GJ-Z datasheet, MP174GJ-Z pinout, MP174GJ-Z application, or MP174GJ-Z equivalent, key selection criteria include its 700V/13.5Ω integrated MOSFET, TSOT23-5 package footprint, 2.55V FB reference voltage, 12–15μs minimum off-time, and comprehensive protection suite (OTP, UVLO, OLP, SCP, open-loop detection).

Technical Context

The MP174GJ-Z implements primary-side regulation using a sampled capacitor feedback mechanism-eliminating optocouplers by sensing output voltage via timing-based sampling during freewheeling diode conduction. Its internal error amplifier compares FB voltage against a 2.55V reference and adjusts switching duty via peak-current limiting and variable off-time control.

Green-mode operation dynamically scales both switching frequency and peak current limit downward under light load: frequency drops from ~28kHz at full load to sub-10kHz at no-load, while peak current compresses from 660mA down to ~300mA, enabling <30mW no-load consumption. Protection logic includes 220ms OLP timer, 750–900mA SCP threshold with 180ns blanking, and thermal shutdown at 150°C with 30°C hysteresis.

Key Specifications

Pinout & Package

MP174GJ-Z is housed in a 5-pin TSOT23-5 package with exposed drain pad for thermal enhancement. Pin 1 = VCC (internal regulator supply), Pin 2 = FB (voltage feedback input), Pins 3 & 4 = SOURCE (MOSFET source, ground reference), Pin 5 = DRAIN (integrated 700V MOSFET drain and HV current source input). No internal connections to pins beyond these five functions.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP174GJ-Z, MP173GJ-Z trades peak output capability and green-mode efficiency for simpler fixed-frequency behavior, while LNK3206G demands more magnetics complexity but offers higher thermal resilience-making MP174GJ-Z optimal for cost-sensitive, space-constrained 5W standby supplies requiring best-in-class no-load performance.

Availability

MP174GJ-Z is available at Aetrix Electronics and suitable for home appliance standby supplies, smart thermostat power systems, and industrial sensor node PSUs requiring stable component supply, RoHS-compliant packaging, and long-term lifecycle support.

Supply support for MP174GJ-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, and global manufacturing partnerships.

The MP174 product line delivers primary-side regulated off-line controllers targeting cost-sensitive, non-isolated AC/DC conversion in consumer and industrial applications-designed to replace optocoupler-based solutions with higher reliability and lower BOM cost.

FAQ

What topologies does MP174GJ-Z support, and which require isolation?

MP174GJ-Z supports Buck, Buck-Boost, Boost, and Flyback topologies. Buck, Buck-Boost, and Boost are non-isolated configurations where output shares ground with input; Flyback provides galvanic isolation via transformer coupling. The IC's primary-side regulation architecture eliminates optocouplers in all cases, but only Flyback inherently isolates input and output circuits.

How does MP174GJ-Z achieve <30mW no-load consumption?

It combines three mechanisms: (1) green-mode frequency foldback-switching frequency drops below 10kHz at no-load; (2) peak-current compression-limit reduces from 660mA to ~300mA as off-time increases; and (3) ultra-low VCC quiescent current (24μA in latch-off phase). These reduce switching and conduction losses simultaneously without external circuitry.

Can MP174GJ-Z operate without an auxiliary VCC winding?

Yes-the IC integrates a high-voltage startup current source connected to the DRAIN pin, enabling self-biasing from the rectified input. An external VCC capacitor (typically 1–10μF) is charged directly from DRAIN during startup and maintained between cycles. No auxiliary winding is required, simplifying transformer design and reducing cost.

What is the role of the feedback capacitor (C_FB) in MP174GJ-Z designs?

C_FB serves as a sample-and-hold capacitor that captures and holds the output voltage during the freewheeling diode conduction period. It enables primary-side regulation by providing a stable DC voltage to the FB pin, allowing the IC to infer output voltage without secondary-side components. Typical values range from 10nF to 100nF depending on output voltage and load dynamics.

How does the open-loop protection function, and what triggers it?

Open-loop protection activates when FB voltage falls below 0.5V for >100μs-indicating loss of feedback signal due to open resistor divider, failed capacitor, or disconnected output. The IC stops switching, discharges VCC to 2.4V, then restarts after VCC recharges to 5.6V. This prevents unregulated high-voltage output during fault conditions, protecting downstream circuitry.

Is MP174GJ-Z compatible with universal AC input (85–265VAC)?

Yes-its 700V integrated MOSFET and internal HV startup circuit support direct connection to rectified universal AC inputs. Design examples confirm stable operation across 85–265VAC with proper input capacitor sizing (e.g., 10μF/400V) and inductor selection (e.g., 1.2mH for 12V/300mA), meeting IEC 61000-4-5 surge immunity requirements.

What thermal considerations apply to the TSOT23-5 package in continuous operation?

The TSOT23-5 package has θ_JA = 100°C/W on a standard 4-layer PCB. At 5W output, junction temperature rise can exceed 125°C without copper pour or thermal vias. Best practice is to connect the exposed DRAIN pad to ≥1cm² internal/external copper plane with ≥4 thermal vias (0.3mm diameter), reducing effective θ_JA to ~60°C/W and enabling reliable 400mA CCM operation at +50°C ambient.