Monolithic Power Systems Inc. MP174AGJ-P

Overview

MP174AGJ-P from Monolithic Power Systems is a 700V primary-side constant-voltage (CV) regulator with integrated MOSFET, supporting buck, buck-boost, boost, and flyback topologies in non-isolated off-line power supplies. It delivers up to 400mA output current in CCM mode, achieves <30mW no-load power consumption, and features frequency foldback and peak-current compression for high light-load efficiency - deployed in home appliance standby rails and white-goods auxiliary power.

For engineers reviewing the MP174AGJ-P datasheet, MP174AGJ-P pinout, MP174AGJ-P application, or MP174AGJ-P equivalent, key selection criteria include its TSOT23-5 package footprint, 700V/13.5Ω internal MOSFET, 2.55V FB reference, thermal shutdown at 150°C, and green-mode operation enabling EN55022-compliant EMI performance without optocoupler.

Technical Context

The MP174AGJ-P implements primary-side regulation using an internal error amplifier that samples FB voltage 6μs after MOSFET turn-off and compares it to a 2.55V reference. Its green-mode control dynamically reduces both switching frequency and peak current limit under decreasing load - achieving <30mW no-load consumption while maintaining stable CV regulation across universal AC input (85–265VAC).

Protection logic includes auto-restart OLP triggered by FB <1.7V for ≥220ms, SCP activation at 750–900mA peak current with 180ns blanking, open-loop detection at FB <0.5V, and OTP recovery hysteresis of 30°C. The IC uses leading-edge blanking (350ns) and ramp compensation scaled to load conditions to ensure stable operation in CCM and DCM.

Key Specifications

Pinout & Package

MP174AGJ-P is housed in a thermally enhanced TSOT23-5 package with exposed drain pad for improved heat dissipation. Pin 1 is VCC (IC supply), Pin 2 is FB (voltage feedback input), Pins 3 and 4 are SOURCE (MOSFET source and ground reference), and Pin 5 is DRAIN (HV MOSFET drain and current-source input). Pins 3/4 are internally tied and must be connected to system ground.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP174AGJ-P, MP173AGJ-Z trades off green-mode efficiency and 700V robustness for lower unit cost, while LNK3206G offers higher integration density but sacrifices light-load performance and design flexibility in output voltage programming.

Availability

MP174AGJ-P is available at Aetrix Electronics and suitable for home appliance auxiliary power, white-goods standby supply, and consumer electronics wall adapters requiring stable component supply, RoHS-compliant packaging, and long-term lifecycle support.

Supply support for MP174AGJ-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, and manufacturing partners qualified to ISO 9001 and IATF 16949 standards.

The MP174A product line targets cost-sensitive, low-power offline AC/DC conversion - designed specifically for primary-side regulation in non-isolated topologies to eliminate optocouplers and reduce system-level BOM count and footprint.

FAQ

What is the maximum continuous output power achievable with MP174AGJ-P in buck topology?

The MP174AGJ-P supports up to 5W output power in buck configuration under typical conditions (85–265VAC input, 12V/300mA output). This is limited by thermal constraints of the TSOT23-5 package (1W P_D at T_A = 25°C) and the 400mA CCM current limit. For sustained 5W operation, PCB copper area and airflow must be optimized per JEDEC JESD51-7 thermal test board guidelines.

Can MP174AGJ-P operate without an external VCC capacitor?

No - an external VCC capacitor (typically 1–4.7μF ceramic) is mandatory. The IC relies on this capacitor to sustain internal circuitry between charging pulses from the internal HV current source. Without it, VCC collapses below 3.4V after startup, triggering shutdown. The capacitor also filters noise on the VCC rail to prevent false UVLO trips during transient load steps.

How does the MP174AGJ-P achieve constant voltage regulation without an optocoupler?

It uses primary-side sensing: the FB pin monitors a sampling capacitor (C3) charged during the freewheeling phase via the output rectifier. This capacitor holds the output voltage level, allowing the IC to regulate based on the 2.55V internal reference. Timing-based sampling (6μs after MOSFET turn-off) compensates for diode forward voltage drop and ensures accurate regulation independent of secondary-side components.

What is the purpose of the dual leading-edge blanking times (350ns and 180ns)?

The 350ns blanking applies during normal switching to suppress turn-on spikes from parasitic capacitance and diode reverse recovery. The shorter 180ns blanking is active only during short-circuit protection detection - enabling faster SCP response while avoiding false triggers during normal high-dI/dt transitions. Both are hard-wired and not user-adjustable.

Is MP174AGJ-P suitable for use in flyback topology with isolation?

Yes - the datasheet explicitly lists flyback as a supported topology. In isolated flyback, the FB signal is derived from an auxiliary winding or reflected voltage across the primary, eliminating the need for optocoupler feedback. However, transformer design must account for the 700V MOSFET rating and ensure proper coupling for accurate voltage reflection during regulation.

Does MP174AGJ-P require a dummy load for stable regulation?

A 2–3mA dummy load is recommended for reliable light-load regulation, especially below 10% of rated output current. This ensures sufficient inductor energy to charge the sampling capacitor (C3) and maintain FB voltage accuracy. For ultra-low-noise applications where regulation is secondary, a Zener diode can replace the resistive dummy load to reduce no-load consumption further.

How does frequency foldback interact with peak-current compression under no-load conditions?

Under no-load, frequency foldback extends the MOSFET off-time, which directly triggers peak-current compression - reducing the ILimit threshold from 660mA toward ~300mA. This dual reduction minimizes both switching and conduction losses, enabling the <30mW no-load specification. The relationship is governed by Equation (5): I_Peak = 660mA − 4.8mA/μs × (τ_Off − 12μs).