Monolithic Power Systems Inc. MP8125EF-LF-P

Overview

MP8125EF-LF-P 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 with 1V line-drop compensation, 22kHz tone generation, and POK indicator - designed specifically for satellite set-top box RF front-end power delivery over coaxial cable.

For engineers reviewing the MP8125EF-LF-P datasheet, MP8125EF-LF-P pinout, MP8125EF-LF-P application, or MP8125EF-LF-P equivalent, key selection criteria include DiSEqC-compliant 22kHz modulation timing (≤1.5 tone periods), programmable current limit (600–1100mA), ±12% POK window, thermal shutdown at 150°C, and dual-package support (TSSOP-16 with exposed pad).

Technical Context

The MP8125EF-LF-P implements a fixed-frequency (352kHz) peak-current-mode boost stage followed by a tracking LDO that maintains minimal dropout (0.9V @ 500mA) while rejecting switching noise from the RF-sensitive LNB path. Its internal 22kHz oscillator synchronizes to the boost frequency (16× ratio), enabling clean DiSEqC signaling without external clock sources.

Control logic includes three dedicated digital inputs: 13V/18V for polarization selection, LINEDROP for +1V coaxial voltage compensation, and EXTM for tone activation/deactivation with ≤1.5-period latency. Protection features are hardware-asserted - dynamic overload (50ms on / 2s off), short-circuit, and thermal shutdown with 20°C hysteresis.

Key Specifications

Pinout & Package

MP8125EF-LF-P is packaged in thermally enhanced TSSOP-16 with exposed pad (connected to PGND), optimized for satellite receiver PCB layouts requiring low EMI and efficient heat dissipation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP8124EF-LF-Z, the MP8125EF-LF-P offers identical pinout and feature set but with slightly higher IQ and narrower temp range - making it viable for cost-constrained legacy STBs. Versus LMX2531, it delivers full DiSEqC autonomy at the expense of RF synthesis capability.

Availability

MP8125EF-LF-P is available at Aetrix Electronics and suitable for satellite set-top boxes, multi-switch distribution systems, and motorized dish controllers requiring stable component supply with full DiSEqC 1.x functionality.

Supply support for MP8125EF-LF-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 core expertise in DC/DC conversion, LED 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 - prioritizing low noise, coaxial signal integrity, and integrated control functionality over general-purpose voltage regulation.

FAQ

What is the function of the TCAP pin on MP8125EF-LF-P?

The TCAP pin provides a 7μA constant current source to charge an external capacitor, setting the soft-start rise time of VOUT. A larger capacitor slows the ramp rate to prevent inrush current into downstream LNB circuitry. Placement must be near SGND with minimal trace length to avoid noise coupling into the reference path.

Can MP8125EF-LF-P operate with input voltage below 8V?

No. The device incorporates an under-voltage lockout (UVLO) that disables regulation when VIN falls below 7V (typical turn-on threshold is 8V). Operation below 8V is outside specified conditions and may cause unstable output or failure to initiate boost conversion.

How does the LINEDROP pin affect output voltage accuracy?

When LINEDROP is driven high, the output voltage increases by exactly 1V (e.g., 13.2V → 14.2V, 18.14V → 19.14V) to compensate for IR drop across long coaxial cables. This offset is trimmed and stable across temperature, ensuring LNB receives nominal bias despite cable resistance.

Is MP8125EF-LF-P pin-compatible with MP8124EF-LF-Z?

Yes - MP8124EF-LF-Z uses identical TSSOP-16 pinout and footprint as MP8125EF-LF-P, including matching SGND, PGND, VOUT, and EXTM assignments. No PCB redesign is needed when upgrading, though firmware may require minor timing adjustments for the faster POK response.

What is the maximum allowable output current with ILIMIT resistor set to 10kΩ?

With a 10kΩ resistor from ILIMIT to GND, the output current limit is calculated as 8500 / 10 = 850mA (typical). This exceeds the 550mA continuous rating, so thermal derating must be applied - junction temperature must remain ≤125°C under full load in the TSSOP-16 package.

Does the POK output require an external pull-up resistor?

Yes. POK is an open-drain output and must be pulled up to a logic-compatible voltage (e.g., 3.3V or 5V) with a 10kΩ resistor to interface with MCU GPIO or supervisor ICs. Without pull-up, POK cannot assert high and will remain floating or low, preventing accurate power-good detection.

Why does MP8125EF-LF-P use a tracking architecture instead of fixed boost voltage?

Tracking minimizes LDO dropout voltage by aligning VBOOST just above VOUT - reducing power dissipation and thermal stress. At 500mA, this cuts LDO loss by ~40% versus a fixed 20V boost, enabling higher efficiency and smaller thermal pads in space-constrained STB designs.