Monolithic Power Systems Inc. MP155GJ-Z

Overview

MP155GJ-Z from Monolithic Power Systems is a primary-side, green-mode off-line regulator IC with integrated 500V/20Ω MOSFET, supporting Buck, Buck-boost, Boost, and Flyback topologies. It delivers up to 4W output power, achieves <100mW no-load consumption, and provides constant voltage regulation without opto-coupler. It targets low-power AC/DC conversion in home appliance standby supplies and white-goods auxiliary power rails.

For engineers reviewing the MP155GJ-Z datasheet, MP155GJ-Z pinout, MP155GJ-Z application, or MP155GJ-Z equivalent, key selection criteria include its primary-side CV control architecture, 500V drain rating, TSOT23-5 package constraints, thermal shutdown with auto-restart, and frequency foldback behavior under light load.

Technical Context

The MP155GJ-Z implements primary-side constant voltage regulation using sampled output voltage held on an external capacitor, eliminating opto-coupler dependency. Its internal 500V MOSFET enables direct high-voltage switching, while feedback is referenced to SOURCE (ground) via the FB pin with 2.55V typical threshold.

Green-mode operation is achieved through simultaneous frequency foldback and peak current compression as load decreases - switching frequency drops below 37kHz and ILimit reduces from 290mA down to ~260mA at light load, enabling <100mW no-load input power. Protection logic includes timer-based OLP (170ms delay), SCP (450mA trigger), and open-loop detection (60mV FB threshold).

Key Specifications

Pinout & Package

MP155GJ-Z is packaged in TSOT23-5 - a thermally enhanced, surface-mount 5-pin package with exposed drain pad for improved heat dissipation. The package supports reflow soldering and fits compact PCB layouts in space-constrained appliances.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP157GJ-Z, MP155GJ-Z trades 150V headroom and 1W output for 22mW lower no-load power and smaller TSOT23-5 footprint; versus LNK3206P, it eliminates opto-coupler drift risk and cuts standby loss by 50mW - critical for CE-marked white goods.

Availability

MP155GJ-Z is available at Aetrix Electronics and suitable for home appliance control boards, smart HVAC auxiliary supplies, and industrial IoT sensor node power rails requiring stable component supply, RoHS-compliant sourcing, and long-lifecycle availability.

Supply support for MP155GJ-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 manufacturing partners across Asia.

The MP155 belongs to MPS's Green-Mode Primary-Side Regulator product line, engineered specifically for cost-sensitive, low-power offline AC/DC conversion in consumer and white-goods applications where opto-coupler elimination and ultra-low standby loss are critical.

FAQ

What is the maximum recommended output power for MP155GJ-Z in TSOT23-5 package?

The MP155GJ-Z in TSOT23-5 is rated for up to 4W continuous output power under proper thermal layout - including connection of the exposed drain pad to ≥2 cm² copper pour. Derating is required above +85°C ambient; at 105°C, max output drops to ~2.5W due to thermal limits and θJA = 100°C/W.

Can MP155GJ-Z operate in discontinuous conduction mode (DCM) only?

No - MP155GJ-Z supports both DCM and CCM operation depending on inductor value and load. At full load (e.g., 200mA @ 12V), it typically operates in CCM; at light load (<30mA), it transitions to DCM automatically via frequency foldback and peak current reduction, maintaining regulation down to zero load.

How does the MP155GJ-Z achieve constant voltage without an opto-coupler?

It uses primary-side sampling: an external capacitor holds the output voltage during MOSFET off-time, and the FB pin senses this held voltage. Internal error amplifier compares it to 2.55V reference and adjusts ON-time to maintain regulation - eliminating need for secondary-side feedback components.

What is the purpose of the 350ns leading-edge blanking (LEB) function?

The 350ns LEB disables the current-sense comparator immediately after MOSFET turn-on to ignore parasitic ringing from drain-source capacitance and layout inductance. This prevents false over-current triggering and ensures accurate peak current limiting during each switching cycle.

Does MP155GJ-Z require an external VCC supply capacitor?

Yes - a 4.7μF–10μF electrolytic or ceramic capacitor must be placed between VCC and SOURCE pins. It stores energy during switching and sustains control circuitry during light-load frequency foldback; undersized VCC caps cause erratic regulation or UVLO cycling.

Is MP155GJ-Z pin-compatible with MP155GS in SOIC8?

No - MP155GJ-Z (TSOT23-5) and MP155GS (SOIC8) share identical electrical functionality but differ in pin count and mapping: TSOT23-5 uses 5 pins (VCC, FB, SOURCE×2, DRAIN), while SOIC8 adds NC pins and separates SOURCE terminals. PCB layout and thermal design are not interchangeable.

What failure modes trigger auto-restart versus latch-off behavior?

Thermal shutdown (TSD), short-circuit (SCP), and open-loop faults trigger auto-restart: VCC discharges to 2.4V, then internal HV current source recharges it to 5.6V for restart. Overload protection (OLP) and sustained UVLO below 3.4V result in latch-off until AC input is cycled or VCC is externally reset.