Monolithic Power Systems Inc. MP155GS-P

Overview

MP155GS-P from Monolithic Power Systems is a primary-side constant-voltage 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 operates across -40°C to +125°C junction temperature for home appliance standby power supplies.

For engineers reviewing the MP155GS-P datasheet, MP155GS-P pinout, MP155GS-P application, or MP155GS-P equivalent, this page provides verified topology support (Flyback/Buck), green-mode frequency foldback behavior, thermal shutdown with auto-restart, VCC UVLO hysteresis (250mV), and primary-side regulation eliminating optocoupler dependency.

Technical Context

The MP155GS-P implements primary-side constant-voltage control using sampled output voltage via an internal 2.55V FB reference and 18μs minimum OFF-time timing. Its green-mode operation dynamically reduces both peak current (290mA typ → lower under light load) and switching frequency as load decreases, enabling high average efficiency in low-power offline converters.

Protection architecture includes timer-based overload detection (170ms delay at 37kHz), short-circuit shutdown at 450mA peak current, open-loop detection at 60mV FB, and thermal shutdown at 150°C with auto-restart. Internal leading-edge blanking (350ns) prevents false current-sense triggering during MOSFET turn-on transients.

Key Specifications

Pinout & Package

MP155GS-P is packaged in SOIC-8 with exposed drain pad for thermal enhancement. Pin 1 is VCC, Pin 2 is FB, Pins 3 and 4 are SOURCE (internally tied), Pin 7 is DRAIN, and Pins 5, 6, and 8 are not connected.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP155GS-P, MP157GS-Z offers higher voltage headroom and power capability but requires layout revalidation; LNK304DG trades primary-side simplicity for tighter regulation at the cost of component count and light-load efficiency.

Availability

MP155GS-P is available at Aetrix Electronics and suitable for home appliance standby power, industrial sensor auxiliary supplies, and IoT gateway always-on rails requiring stable component supply across extended temperature and long-lifecycle programs.

Supply support for MP155GS-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, Washington, with global design and support centers.

The MP155 product line targets cost-sensitive, low-power offline AC/DC conversion where primary-side regulation, green-mode efficiency, and integration reduce system size and bill-of-materials-especially in white goods and consumer standby applications.

FAQ

What topologies does MP155GS-P support, and which require isolation?

MP155GS-P supports Buck, Buck-boost, Boost, and Flyback topologies. Only Flyback provides galvanic isolation due to its transformer-coupled architecture; the others are non-isolated and suitable for applications where primary-side grounding is acceptable, such as internal auxiliary rails in appliances.

How does MP155GS-P achieve <100mW no-load power consumption?

It combines green-mode operation-reducing both switching frequency and peak current under light load-with an internal high-voltage current source that powers the IC directly from the DRAIN pin, eliminating the need for a dedicated auxiliary winding or linear regulator, thereby minimizing quiescent losses.

Can MP155GS-P replace optocoupler-based controllers in existing designs?

Yes, but layout and compensation must be revised: remove optocoupler and TL431, add sampling capacitor per the typical application schematic, and adjust feedback resistors to set V_FB = 2.55V. The SOIC8 footprint allows drop-in replacement only if thermal and EMI constraints are re-validated.

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

The LEB disables the current comparator for 350ns after MOSFET turn-on to suppress false triggering caused by parasitic ringing at the source node. This ensures accurate peak-current limiting and stable operation even with fast-switching layouts and high dv/dt waveforms.

Does MP155GS-P support adjustable switching frequency?

No-MP155GS-P uses variable-frequency green-mode control where switching frequency decreases with load. Typical nominal frequency is ~37kHz at full load, dropping to <10kHz at light load. Fixed-frequency operation is not supported; frequency foldback is inherent to its efficiency architecture.

How is open-loop protection triggered, and what happens afterward?

Open-loop protection activates when FB voltage falls below 60mV for more than 128 switching cycles (blanked during startup). The IC shuts down, discharges VCC via 16μA internal current source, and auto-restarts once VCC drops below 2.4V and is recharged by the high-voltage regulator.

What is the maximum continuous output current in CCM and DCM modes?

In continuous conduction mode (CCM), MP155GS-P supports up to 220mA output current; in discontinuous conduction mode (DCM), it supports up to 130mA. These values assume proper inductor selection, thermal management, and input voltage conditions per the datasheet's P_min vs. L curves.