Monolithic Power Systems Inc. MP155GJ-P

Overview

MP155GJ-P from Monolithic Power Systems is a primary-side, green-mode off-line regulator 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 in home appliance standby supplies.

For engineers reviewing the MP155GJ-P datasheet, MP155GJ-P pinout, MP155GJ-P application, or MP155GJ-P equivalent, key selection criteria include its TSOT23-5 package, 500V drain rating, 2.55V feedback threshold, thermal shutdown at 150°C, and frequency foldback behavior under light load.

Technical Context

The MP155GJ-P implements primary-side constant voltage control using sampled output voltage held on an external capacitor, eliminating opto-coupler dependency. Its internal high-voltage current source enables direct Drain-pin startup, and VCC regulation operates between 5.3V (turn-on) and 5.6V (turn-off) with 250mV hysteresis.

It employs adaptive peak current compression and minimum OFF-time limiting (18μs normal, soft-starting from 72μs), enabling efficient DCM operation down to 130mA and CCM up to 220mA. Protection logic includes timer-based OLP (170ms delay at 37kHz), SCP at 450mA, and open-loop detection at 60mV FB voltage.

Key Specifications

Pinout & Package

MP155GJ-P is housed in a TSOT23-5 package with exposed drain pad for thermal enhancement. Pin 1 = VCC, Pin 2 = FB, Pins 3–4 = SOURCE (internally tied), Pin 5 = DRAIN. No internal connections to pins marked N/C in SOIC8 variant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP155GJ-P, MP157GJ-Z extends voltage margin and power capability within identical TSOT23-5 layout, while LNK3206G trades primary-side simplicity for tighter regulation-making MP155GJ-P optimal for cost-sensitive, space-constrained 4W standby supplies where ±5% CV is acceptable.

Availability

MP155GJ-P is available at Aetrix Electronics and suitable for home appliance control panels, industrial sensor nodes, and IoT gateway standby power requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MP155GJ-P 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, headquartered in Kirkland, WA, with global design and support centers.

The MP155 product line targets ultra-low-power offline AC/DC conversion for consumer and industrial applications, emphasizing integration, efficiency at light load, and simplified system-level design through primary-side regulation.

FAQ

What topologies does MP155GJ-P support, and which require isolation?

MP155GJ-P supports Buck, Buck-boost, Boost, and Flyback topologies. Only Flyback provides galvanic isolation; the others are non-isolated and deliver referenced output voltages. Flyback requires a transformer with auxiliary winding for VCC supply, while Buck/Buck-boost/Boost use direct DC-link connection.

How does MP155GJ-P achieve constant voltage regulation without an opto-coupler?

MP155GJ-P samples the output voltage via a capacitor charged during the MOSFET OFF period, then holds that voltage on the FB pin. The internal comparator compares this sampled value to a 2.55V reference, adjusting ON-time to maintain regulation-eliminating need for secondary-side feedback components.

What is the significance of the 350ns leading-edge blanking (LEB) time?

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 premature switching termination and ensures stable current-limiting across varying PCB layouts and MOSFET types.

Can MP155GJ-P operate with universal AC input (85–265VAC)?

Yes-MP155GJ-P's 500V drain rating and internal high-voltage startup circuit enable direct connection to rectified universal AC input. Designers must select appropriate input capacitor (e.g., 3µF/W for half-wave) and ensure minimum DC bus stays above 70V to avoid UVLO-induced shutdown.

What is the role of the dummy load in MP155GJ-P designs?

A 3mA dummy load ensures sufficient inductor energy transfer during light-load conditions to reliably charge the external sampling capacitor. Without it, FB voltage may collapse below 60mV, triggering open-loop protection and disabling regulation-especially critical in always-on appliance standby rails.

How does frequency foldback improve light-load efficiency?

As load decreases, MP155GJ-P reduces both switching frequency and peak current limit. Lower frequency cuts switching losses (proportional to f_sw), while reduced peak current lowers conduction loss in the integrated MOSFET-jointly achieving <100mW no-load consumption and >75% efficiency at 10% load.