Monolithic Power Systems Inc. MP4078GS-P

Overview

MP4078GS-P from Monolithic Power Systems is a primary-side regulation (PSR) offline controller with integrated active PFC for constant-voltage LED drivers and front-end pre-regulators. It operates in discontinuous conduction mode (DCM) with valley switching, achieves <50 mW no-load consumption at 230 VAC, supports universal input (85–277 VAC), and integrates a 35 V/320 mΩ internal low-side MOSFET in SOIC-8.

For engineers reviewing the MP4078GS-P datasheet, MP4078GS-P pinout, MP4078GS-P application, or MP4078GS-P equivalent, this device enables optocoupler-free flyback and buck-boost topologies with COT control, fast start-up via cascode architecture, and comprehensive protection including OVP (2.96 V), SCP (200 mV), OCP (2.0 V), and OTP (160 °C).

Technical Context

The MP4078GS-P implements constant-on-time (COT) control with input voltage sensing via the MULT pin to maintain high power factor (>0.9 at full load) and low THD across universal AC input. Its on-time generator uses a slew-rate capacitor charged by VMULT-derived current and compared against COMP voltage, with VCOMP_HALF (2.2 V) enabling fixed on-time under light load.

Primary-side regulation relies on zero-current detection (ZCD pin, 100 mV threshold, 300 ns turn-on delay) and adaptive blanking (tZCD_DELAY = 1.16–1.79 µs based on S-pin current), while valley switching reduces switching loss. Protection logic includes latched SCP (6 ms duration), auto-restart OVP (2.96 V), and thermal shutdown with 60 °C hysteresis.

Key Specifications

Pinout & Package

MP4078GS-P is housed in a standard SOIC-8 package with exposed pad (no thermal pad designation in datasheet), rated MSL Level 2, and optimized for surface-mount assembly on 4-layer PCBs (θ_JA = 96 °C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar primary-side regulation with active PFC applications.

Compared with MP4077GS-P, MP4078GS-P offers lower system cost and smaller layout for ≤25 W LED drivers due to its integrated MOSFET, while UCC28056DR+UCC28740 delivers superior harmonic performance at the expense of complexity and board area-making MP4078GS-P optimal for cost-sensitive, space-constrained CV LED applications.

Availability

MP4078GS-P is available at Aetrix Electronics and suitable for smart LED lighting, front-end pre-regulators, AC-DC adapters, and IoT gateway power supplies requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for MP4078GS-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 power management ICs, with over 20 years of expertise in DC-DC, AC-DC, LED drivers, and motor drivers.

The MP4078 product line targets cost-sensitive, high-volume offline power conversion applications-specifically constant-voltage LED drivers and universal-input pre-regulators-where integration, efficiency, and regulatory compliance are critical.

FAQ

What is the minimum recommended R_ZCD1//R_ZCD2 value for stable ZCD sensing?

The datasheet specifies two validated configurations: 2.8–3.3 kΩ yields tCYCLE_MIN = 15.3 µs and KSLEW = 9×10⁻⁷ s, while >8.8 kΩ gives tCYCLE_MIN = 11 µs and KSLEW = 4.5×10⁻⁷ s. Using values outside this range risks inaccurate ZCD timing, leading to output regulation drift or instability under light load.

Does MP4078GS-P support quasi-resonant (QR) operation?

No. MP4078GS-P operates exclusively in discontinuous conduction mode (DCM) with valley switching-not true QR. It detects zero-current via the ZCD pin and triggers turn-on after a fixed 300 ns delay, but does not dynamically adjust switching frequency to track resonant peaks like dedicated QR controllers.

How is brownout protection implemented and what is its response time?

Brownout is detected when VMULT falls below 210 mV (typ.), with 110 mV hysteresis and a 24 ms detection window (tMULT_BO). Once triggered, the IC halts switching and enters UVLO until VMULT rises above 320 mV (brown-in threshold), ensuring clean restart without output droop or latch-up.

Can MP4078GS-P be used in isolated forward converter topologies?

No. The MP4078GS-P is designed specifically for flyback and non-isolated buck-boost topologies. Its ZCD-based PSR algorithm relies on auxiliary winding voltage proportional to output voltage-a condition not met in forward converters, which require different sensing methods and lack inherent reset mechanisms compatible with this IC's control scheme.

What is the maximum allowable R_SENSE value for OCP calibration?

R_SENSE must be selected so that peak primary current produces ≤2.0 V at the S pin. With VCS_OCP = 2.0 V (typ.) and typical primary peak current of 1.2 A in 25 W designs, R_SENSE ≤ 1.67 Ω. Exceeding this causes premature OCP triggering; values below 1.0 Ω improve noise immunity but reduce current-sense resolution.

Is the internal MOSFET rated for continuous 600 mA drain current?

No. The 320 mΩ R_DS(ON) is specified at 100 mA and 25°C. At 600 mA, power dissipation exceeds the SOIC-8 package's 1.3 W limit unless aggressively heatsinked. The IC is intended for peak currents ≤600 mA in DCM flyback, where duty cycle keeps average current well below 100 mA-ensuring safe junction temperature.

How does the COMP pin clamp behavior affect loop stability?

The COMP pin clamps between 0.05 V (VCOMPL) and 4.25 V (VCOMPH), preventing integrator windup during transients. This hard clamping maintains phase margin during large load steps, but requires careful RC compensation design-especially the zero placed near 1 kHz-to avoid oscillation when VCOMP approaches either rail during startup or overload recovery.