Monolithic Power Systems Inc. MP8125EF-LF

Overview

MP8125EF-LF from Monolithic Power Systems is a DiSEqC 1.x–compliant LNB power supply and control voltage regulator integrating a current-mode boost converter and tracking linear regulator. It delivers up to 550mA output at selectable 13V/18V (±0.4V load regulation), supports 22kHz tone modulation via EXTM pin, provides 1V line-drop compensation, and operates from 8V–14V input. It powers satellite RF LNBs in set-top boxes via coaxial cable while preserving signal integrity.

For engineers reviewing the MP8125EF-LF datasheet, MP8125EF-LF pinout, MP8125EF-LF application, or MP8125EF-LF equivalent, this device is selected for LNB biasing with integrated DiSEqC signaling, precise output voltage selection, dynamic current limiting, thermal shutdown, and POK monitoring - all critical for satellite receiver front-end power design.

Technical Context

The MP8125EF-LF implements a two-stage architecture: a fixed-frequency (352kHz) peak-current-mode boost converter followed by a tracking LDO. The boost stage regulates VBOOST to track VOUT + dropout (0.9V typ.), minimizing LDO dissipation. Its internal oscillator generates a 22kHz tone synchronized to the boost frequency (16× ratio) for DiSEqC-compliant signaling.

Voltage selection (13V/18V) and line-drop compensation (+1V) are controlled by logic-level inputs (13V/18V and LINEDROP pins), while soft-start timing is set via external capacitor on TCAP (7μA charging current). Overcurrent protection uses programmable ILIMIT (600–1100mA range) with 50ms on-time / 2s off-time restart behavior.

Key Specifications

Pinout & Package

MP8125EF-LF is housed in a thermally enhanced TSSOP-16 package with exposed pad (connected to SGND/PGND), optimized for compact satellite receiver PCB layouts and moderate power dissipation (2.8W @ TA=25°C).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LNB power supply and control applications.

Compared with MP8125EF-LF, MP8124EF-LF offers higher efficiency and broader temperature support for new designs, while LMX2531LQ1730E provides RF synthesis capability but omits essential DiSEqC functions - making MP8125EF-LF irreplaceable in cost-sensitive, standards-compliant satellite receivers.

Availability

MP8125EF-LF is available at Aetrix Electronics and suitable for satellite set-top boxes, multi-switch LNB systems, long-run coax distribution networks, and outdoor antenna modules requiring stable component supply and DiSEqC 1.x compliance.

Supply support for MP8125EF-LF 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 core expertise in DC/DC conversion, motor drivers, and satellite power solutions.

The MP8125 belongs to MPS's LNB power management product line, engineered specifically for DiSEqC-compliant satellite receiver front-ends - balancing low noise, precise voltage control, and integrated signaling in space-constrained consumer electronics.

FAQ

What is the maximum recommended output current for continuous operation?

The MP8125EF-LF delivers up to 550mA continuously under specified conditions (TA ≤85°C, proper PCB thermal layout). At 500mA, dropout is 0.9V typ., and thermal shutdown triggers at 150°C junction temperature. Derating is required above 85°C ambient or with inadequate copper area on the exposed pad.

How does the 22kHz tone get applied to the output?

The internal 22kHz oscillator modulates the VOUT rail directly when EXTM is high. The tone appears as a small AC component superimposed on the DC output voltage, with peak-to-peak amplitude of 0.55–0.9V into 0–100mA load. No external coupling components are needed - it is designed for direct coax transmission.

Can the MP8125EF-LF be used without the LINEDROP compensation feature?

Yes - tie LINEDROP to GND (logic low) to disable the +1V offset. In this configuration, VOUT is 12.8–13.6V (13V mode) or 17.6–18.7V (18V mode) across 10–100mA load. Leaving LINEDROP floating is prohibited and may cause undefined output behavior.

What is the purpose of the TCAP pin, and how is soft-start time calculated?

TCAP accepts an external capacitor charged by a 7μA internal current source to control VOUT ramp rate. Soft-start time tSS ≈ (CSS × VOUT) / 7μA. For example, a 100nF capacitor yields ~270ms rise time to 19V. Place CSS close to TCAP and SGND, away from noisy SW traces.

Is the MP8125EF-LF RoHS compliant and lead-free?

Yes - the "-LF" suffix denotes lead-free, RoHS-compliant packaging. All MPS parts meet EU RoHS Directive 2011/65/EU requirements, including restrictions on Pb, Cd, Hg, Cr⁶⁺, PBB, and PBDE. Full compliance documentation is available on the MPS Quality Assurance website.

Why is the MP8125 marked "Not Recommended for New Designs"?

MPS explicitly states this in the datasheet due to the introduction of the upgraded MP8124EF-LF, which offers higher efficiency, lower IQ, wider temperature range, and continued long-term supply. MP8125 remains fully supported for existing designs but is not qualified for new product introductions.

How is current limit set using the ILIMIT pin?

A resistor R_LIMIT from ILIMIT to GND programs the current threshold per I_LIMIT = 8500 / R_LIMIT (Ω). For 850mA limit, use 10kΩ; for 600mA, use 14.2kΩ. The device enters foldback after 50ms overload and auto-restarts after 2s - no external circuitry needed for protection.