Monolithic Power Systems Inc. MP171GS-P

Overview

MP171GS-P 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 incorporates thermal shutdown, OLP, SCP, and open-loop protection. It targets low-power standby supplies in home appliances and white goods.

For engineers reviewing the MP171GS-P datasheet, MP171GS-P pinout, MP171GS-P application, or MP171GS-P equivalent, this page provides verified topology support, real-world CV regulation behavior, validated protection thresholds, and package-specific thermal performance data - all critical for offline flyback or buck converter design at ≤2 W output.

Technical Context

The MP171GS-P implements primary-side CV regulation using internal error amplifier sampling of a feedback capacitor (C3), eliminating optocoupler dependency. Its 2.55 V FB reference voltage directly sets output via R1/R2 divider, and ramp compensation improves load regulation by dynamically adjusting comparator threshold relative to MOSFET off time.

It operates in green-mode: switching frequency and peak current limit both scale down under light load, reducing switching losses and enabling <30 mW no-load consumption. Protection logic includes auto-restart OLP (175 ms delay), latch-off SCP (300 mA threshold), and thermal shutdown at 150°C with 30°C hysteresis.

Key Specifications

Pinout & Package

MP171GS-P is housed in an SOIC-8 package with exposed pad for thermal enhancement. Pin 1 is VCC, Pin 2 is FB, Pins 3 and 4 are SOURCE (common ground reference for VCC and FB), Pin 7 is DRAIN (HV MOSFET drain terminal), and Pins 5, 6, and 8 are NC (no connection).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP171GS-P, MP171A-GS-Z offers improved production consistency and extended lifecycle support, while LNK304DG-TL trades primary-side simplicity for isolation capability and higher power - making MP171GS-P optimal for cost-sensitive, non-isolated ≤2 W applications where optocoupler elimination is critical.

Availability

MP171GS-P 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 and long-term obsolescence management.

Supply support for MP171GS-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, with design centers in the US, China, and Taiwan.

The MP171 product line delivers primary-side offline regulators targeting ultra-low-noise, non-isolated AC/DC conversion for energy-efficient consumer and industrial standby power applications.

FAQ

What topologies does MP171GS-P support?

MP171GS-P supports buck, boost, buck-boost, and flyback topologies in non-isolated configurations. It uses primary-side sampling for CV regulation without optocouplers. Flyback operation requires a coupled inductor and indirect feedback via a sampling capacitor on the primary side, as confirmed in the Typical Application Circuits section of the datasheet.

Why is MP171GS-P marked "Not Recommended for New Designs"?

MP171GS-P is superseded by the MP171A series, which features tighter FB reference tolerance (±1.5% vs ±3.9%), improved OLP timing consistency, and extended manufacturing support. The original MP171 remains functional and supported for existing designs but lacks the long-term availability and specification enhancements of the MP171A revision.

How does MP171GS-P achieve <30 mW no-load consumption?

It combines green-mode operation (frequency foldback and peak current compression), low VCC operating current (200 µA quiescent), and internally biased VCC supply. Under no-load, switching frequency drops significantly, and peak current limit decreases, minimizing both switching and conduction losses - verified in Typical Performance Characteristics at 230 VAC input.

What is the role of the sampling capacitor (C3) in MP171GS-P circuits?

C3 samples and holds the output voltage during freewheeling diode conduction, feeding that voltage to the FB pin. Its value directly impacts light-load regulation: too small causes poor CV accuracy at low current; too large slows response. Equation (11) in the datasheet provides sizing guidance based on output voltage, current, and R1/R2 values.

Can MP171GS-P be used in isolated flyback designs?

Yes - it supports isolated flyback using primary-side regulation via a sampling capacitor (C3) referenced to the primary winding. Isolation is achieved through transformer coupling, but feedback remains primary-side only. The datasheet confirms this in Table 1 and Figure 9, noting "indirect feedback" and specifying transformer turns ratio impact on regulation accuracy.

What are the thermal limitations of MP171GS-P in SOIC-8 package?

In SOIC-8, MP171GS-P has θJA = 96 °C/W and θJC = 45 °C/W (per JESD51-7, 4-layer PCB). At 25°C ambient, maximum continuous power dissipation is 1 W before reaching 150°C junction limit. Derating is required above 25°C; for example, at 70°C ambient, max safe power drops to ~0.52 W without heatsinking.

How does open-loop protection trigger in MP171GS-P?

Open-loop protection activates when FB voltage falls below 0.5 V (typical), indicating loss of feedback signal or failed sampling capacitor. The IC stops switching and initiates restart after discharging VCC to VCCpro (2.5 V). During soft-start, this protection is blanked to prevent false triggering during initial power-up.