Monolithic Power Systems Inc. MP173GJ-P

Overview

MP173GJ-P from Monolithic Power Systems is a 700 V non-isolated offline primary-side constant-voltage regulator with integrated MOSFET, supporting buck/boost/buck-boost/flyback topologies. It delivers up to 280 mA output current in CCM, achieves <30 mW no-load power consumption, and operates across -40°C to +125°C junction temperature for home appliance standby power supplies.

For engineers reviewing the MP173GJ-P datasheet, MP173GJ-P pinout, MP173GJ-P application, or MP173GJ-P equivalent, this device requires attention to its TSOT23-5 package constraints, green-mode frequency foldback behavior, primary-side CV regulation without optocoupler, and explicit "not recommended for new designs" status per MPS documentation.

Technical Context

The MP173GJ-P implements primary-side constant-voltage regulation using internal error amplifier sampling of FB voltage 6 µs after MOSFET turn-off, referenced to 2.55 V. Its green-mode operation dynamically reduces both peak current (420 mA → down to ~180 mA) and switching frequency under light load to achieve <30 mW no-load consumption.

It integrates a 700 V, 14–27 Ω (TJ = 25–125°C) MOSFET with leading-edge blanking (350 ns), thermal shutdown at 150°C (30°C hysteresis), and protection logic for OLP (220 ms delay), SCP (600 mA threshold), UVLO (5.1–5.8 V), and open-loop detection (VFB < 0.5 V).

Key Specifications

Pinout & Package

MP173GJ-P is housed in a thermally enhanced TSOT23-5 package with exposed drain pad for improved heat dissipation. The 5-pin configuration supports compact PCB layout while maintaining safe creepage/clearance for 700 V operation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar non-isolated offline regulator applications.

Compared with MP173GJ-P, MP173A-GJ-Z offers guaranteed long-term support and refined protection behavior, while MP174GJ-Z provides higher voltage margin and lower no-load power-both retain identical board layout compatibility but address distinct design-generation and regulatory requirements.

Availability

MP173GJ-P is available at Aetrix Electronics and suitable for home appliance standby supplies, industrial control auxiliary rails, and consumer electronics adapters requiring stable component supply and legacy design continuity.

Supply support for MP173GJ-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 across Asia and North America.

The MP173 product line targets cost-sensitive, low-power offline AC/DC conversion where simplicity, small size, and regulatory compliance are critical-designed specifically for non-isolated primary-side regulation in white goods and consumer standby applications.

FAQ

Is MP173GJ-P still recommended for new designs?

No. Monolithic Power Systems explicitly states "NOT RECOMMENDED FOR NEW DESIGNS. REFER TO MP173A" in all official documentation. MP173GJ-P remains available for legacy production and repair, but MP173A-GJ-Z is the designated replacement with updated specifications, enhanced protections, and ongoing manufacturing support.

What is the maximum output power achievable with MP173GJ-P in TSOT23-5 package?

In TSOT23-5, MP173GJ-P supports up to 4 W output power under typical conditions. This is constrained by thermal limits (θ_JA = 100°C/W) and maximum CCM output current of 280 mA. Derating is required above +85°C ambient; SOIC-8 variant allows higher power due to lower thermal resistance (θ_JA = 96°C/W).

How does MP173GJ-P achieve constant voltage regulation without an optocoupler?

It uses primary-side sensing: a capacitor (C3) samples the output voltage during freewheeling diode conduction and holds it on the FB pin. The internal error amplifier compares this sampled voltage to a 2.55 V reference and adjusts on-time to maintain regulation-eliminating need for secondary-side feedback components.

What are the key differences between MP173GJ-P and MP173A-GJ-Z?

MP173A-GJ-Z features revised OLP timing (tighter 220 ms tolerance), improved EMI performance via optimized gate drive, updated thermal shutdown recovery hysteresis, and extended product lifecycle. Electrical specs (V_FB, R_DS(on), I_LIMIT) remain functionally identical, and pinout/package are fully compatible.

Can MP173GJ-P operate in flyback topology with isolation?

Yes-MP173GJ-P supports flyback topology with transformer isolation. However, regulation becomes indirect: output voltage is inferred from reflected primary waveform, requiring careful transformer turns ratio and snubber design. Accuracy degrades vs. buck/boost due to leakage inductance and coupling variations.

What is the purpose of the dummy load in MP173GJ-P designs?

A 2–3 mA dummy load ensures sufficient inductor energy transfer to charge the FB sampling capacitor (C3) during light/no-load conditions. Without it, C3 discharges below regulation threshold, causing output voltage drift. Zener-based dummy loads reduce no-load consumption when regulation precision is relaxed.

Does MP173GJ-P require an external VCC capacitor?

Yes. A 1–10 µF ceramic capacitor must be placed between VCC and SOURCE pins. It stores energy for control circuitry during MOSFET on-time and is recharged by the internal HV regulator from DRAIN during off-time. Low-ESR construction is mandatory for stable operation.