Monolithic Power Systems Inc. MP8757GL-Z

Overview

MP8757GL-Z from Monolithic Power Systems is a fully integrated, high-frequency synchronous buck converter delivering 7A continuous output current across a 5V–18V input range. It employs Constant-On-Time (COT) control for fast transient response and seamless PFM mode transition at light load, features internal 25mΩ/12mΩ MOSFETs, 500kHz switching frequency, and 0.604V–5.5V adjustable output - deployed in laptop power rails and server point-of-load regulation.

For engineers reviewing the MP8757GL-Z datasheet, MP8757GL-Z pinout, MP8757GL-Z application, or MP8757GL-Z equivalent, key selection considerations include its QFN-21 (3mm×4mm) thermal performance (θJA = 50°C/W), COT-based loop stability with ceramic output capacitors, latch-off reset via EN/power cycle, and integrated OCP/OVP/UVP/thermal shutdown protection.

Technical Context

The MP8757GL-Z implements a proprietary COT control architecture that dynamically adjusts on-time based on input/output voltage to maintain ~500kHz switching frequency across operating conditions. Its valley-current overcurrent protection uses low-side R_DS(ON) sensing (12mΩ) without external sense resistors, and internal ramp compensation enables stable operation with low-ESR ceramic output capacitors.

Power-good signaling is implemented as an open-drain output with 95% V_REF rising threshold and 450μs delay, while soft-start ramps the internal reference over 1.95ms. UVLO is fixed at 4.5V (rising) with 500mV hysteresis, and output discharge is handled by an internal 6Ω MOSFET activated during disable or fault conditions.

Key Specifications

Pinout & Package

MP8757GL-Z is housed in a thermally enhanced QFN-21 package (3mm × 4mm, 0.5mm pitch) with exposed thermal pad (pins 10, 11, 12, 19) connected to PGND for optimal heat dissipation. The layout prioritizes low-inductance SW and PGND paths, with dedicated AGND and GND pins for analog/digital separation.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck converter applications.

Compared with RTQ2962-QA and TPS546B24A, MP8757GL-Z offers superior integration (no external ramp needed, built-in discharge), lower solution cost, and smaller footprint - making it optimal for cost-sensitive, space-constrained applications where analog control suffices.

Availability

MP8757GL-Z is available at Aetrix Electronics and suitable for laptop computer power delivery, server point-of-load conversion, and flat-panel display logic supply requiring stable component supply across extended production lifecycles.

Supply support for MP8757GL-Z 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 global manufacturing partnerships.

The MP8757 belongs to MPS's high-current synchronous buck converter product line, engineered specifically for compact, high-efficiency DC/DC conversion in portable computing and infrastructure equipment where thermal density and transient response are critical.

FAQ

What is the minimum recommended output capacitance for stable operation with MP8757GL-Z?

The MP8757GL-Z supports ceramic output capacitors as small as 22μF (X7R, 1206) when using internal ramp compensation. For 5V output at 7A, MPS recommends ≥47μF total capacitance with ≤5mΩ ESL to ensure <1% output ripple and avoid instability in CCM mode. Bulk capacitance can be reduced by 60% versus electrolytic-based designs.

Does MP8757GL-Z support pre-biased output startup?

Yes. When the FB node is pre-biased above the soft-start target voltage at EN assertion, the MP8757GL-Z disables both high-side and low-side FETs until the internal reference voltage exceeds the sensed FB voltage. This prevents reverse current flow and ensures controlled, non-destructive startup into pre-charged rails.

How is overcurrent protection triggered and reset on MP8757GL-Z?

OCP triggers on valley current exceeding 9.5A, detected via low-side MOSFET R_DS(ON) sensing during the off-state. Upon trip, the controller latches off the high-side FET and holds the low-side FET on until inductor current decays to zero. Reset requires pulling EN low or cycling VIN - no automatic retry to prevent thermal runaway.

Can MP8757GL-Z operate with input voltage below 5V?

No. The absolute minimum operating input voltage is 5V per datasheet specifications. Although UVLO is set at 4.5V, the device is not characterized or guaranteed for stable regulation below 5V due to insufficient headroom for internal LDO (VCC = 5.1V) and gate drive margins across temperature and process variation.

What is the purpose of the exposed thermal pad on the QFN-21 package?

The exposed pad (pins 10, 11, 12, 19) is electrically connected to PGND and serves as the primary thermal path from die to PCB. It must be soldered to a ≥100mm² copper pour with ≥6 thermal vias (0.3mm diameter) to an inner ground plane to achieve the specified θJA of 50°C/W and sustain 7A continuous operation at TA = 85°C.

Is external ramp compensation mandatory for all output capacitor types?

No. Internal ramp compensation enables stable operation with ceramic, POSCAP, and polymer capacitors without external components. External ramp (R4/C4) is only required if instability persists - typically with ultra-low-ESR ceramics (<2mΩ) or very high capacitance (>100μF) configurations where internal compensation is insufficient to suppress subharmonic oscillation.

How does the power-good (PG) signal behave during undervoltage fault conditions?

When FB falls to 85% of VREF, PG is pulled low after a 12μs delay (UVP delay). During latch-off faults (OVP/UVP/thermal), PG remains low until EN is cycled or VIN is power-cycled - it does not assert high again until full soft-start completes and FB stabilizes within 95–105% of target for >450μs.