Monolithic Power Systems Inc. MP4657BGS-Z

Overview

MP4657BGS-Z from Monolithic Power Systems is a single-stage flyback LED driver and system voltage controller for secondary-side LCD backlighting, integrating 4-string LED current balancing (±2% matching), 1.5% VSYS regulation accuracy, and independent PWM/analog dimming control via ADIMP/PWM pin with 5 kHz frequency threshold. It regulates both LED current (up to 80 V per string) and system supply voltage (5 V typical) using one flyback stage plus an external N-channel MOSFET.

For engineers reviewing the MP4657BGS-Z datasheet, MP4657BGS-Z pinout, MP4657BGS-Z application, or MP4657BGS-Z equivalent, key selection considerations include dual-loop control architecture (ICOMP/DCOMP), SOIC-16 package thermal resistance (θJA = 80°C/W), soft-switching MOSFET gate drive (GATE referenced to VIN/SOURCE), and fault detection on ISET/FAULT pin with latch-off behavior.

Technical Context

The MP4657BGS-Z implements dual independent control loops: ICOMP regulates LED current by modulating flyback duty cycle based on minimum VLEDx feedback, while DCOMP controls VSYS by adjusting external MOSFET duty cycle when PWM is active-or directly modulates flyback when PWM is inactive. Its SYNC pin synchronizes GATE turn-off to primary-side flyback switching edge to enable zero-current turn-on.

Dimming mode is determined by ADIMP/PWM input frequency: >5 kHz enables analog dimming (continuous current modulation), <5 kHz enables PWM dimming (current chopping). Protection logic includes OVP latching at 3 V on OVP pin, feedback open-loop detection after 1024 cycles of saturated DCOMP, and LED short detection via slow OV (4.9 V) and fast OV (20 V) thresholds with differentiated delay times.

Key Specifications

Pinout & Package

MP4657BGS-Z is housed in a standard SOIC-16 package (body size 10.3 mm × 7.5 mm, 1.27 mm pitch), rated MSL Level 2, with θJA = 80°C/W and θJC = 35°C/W on 4-layer PCB.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar LED driver and system voltage control applications.

Compared with MP4657BGS-Z, MP4655AGS-Z sacrifices system voltage control for lower cost and smaller footprint, while MPQ4657BGU-AEC1-Z adds automotive qualification and diagnostics at higher unit cost - making MP4657BGS-Z optimal for industrial/commercial LCD backlighting where integration and thermal performance are primary drivers.

Availability

MP4657BGS-Z is available at Aetrix Electronics and suitable for LCD monitor backlighting, smart TV panel control, and flat-panel video display applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant sourcing.

Supply support for MP4657BGS-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 power management ICs, with over two decades of expertise in DC/DC converters, LED drivers, and motor drivers.

The MP4657B product line targets secondary-side LED backlight control in consumer and commercial displays, designed to replace multi-IC solutions with integrated flyback + MOSFET gate control and precision current balancing.

FAQ

What dimming modes does MP4657BGS-Z support, and how are they selected?

The MP4657BGS-Z supports both analog and PWM dimming via the ADIMP/PWM pin. Analog dimming is activated by applying a pulse signal above 5 kHz, which continuously modulates LED current. PWM dimming uses signals below 5 kHz to chop the LED current at the input frequency. The device automatically detects mode based on input frequency - no configuration register or external logic is required.

How does the MP4657BGS-Z handle system voltage regulation when the PWM signal is inactive?

When the PWM signal is inactive (low), the MP4657BGS-Z disables the ILED regulation loop and routes full control of the flyback power stage to the DCOMP loop. The external N-channel MOSFET is held fully on, and VSYS is regulated solely by adjusting flyback duty cycle. This ensures stable 5 V output even during LED disable periods, such as standby or black-frame insertion.

What protections are implemented on the LED string terminals, and how do they respond to faults?

The LEDx pins (7, 8, 11, 10) feature short-to-ground protection, LED open detection (via OVP pin monitoring), and LED short detection using dual-threshold OV sensing (4.9 V slow, 20 V fast) with differentiated delays (5.8 ms vs. 12 ms). Upon fault detection, the ISET/FAULT pin is pulled low and the IC latches off - requiring power cycle to reset - preventing uncontrolled current or voltage stress.

Can MP4657BGS-Z operate without an external optocoupler, and what is the role of the OPT pin?

No - the OPT pin must drive an external optocoupler LED to close the primary-side flyback control loop. It outputs a compensation signal that adjusts primary-side duty cycle based on secondary-side VSYS feedback. If the OPT pin is left unconnected or unterminated, VSYS regulation fails and OVP may trigger due to feedback open-loop detection after 1024 cycles.

What is the maximum allowable LED string voltage, and how is overvoltage protection triggered?

The MP4657BGS-Z supports up to 80 V per LED string, with absolute maximum rating of 80 V on LEDx pins. LED overvoltage protection triggers when the OVP pin voltage exceeds 2.40 V (typical threshold), corresponding to ~80 V at the LED string output depending on divider ratio. If OVP pin voltage reaches 3 V, the IC latches off permanently until power is cycled.

How does the SYNC pin improve efficiency and reliability in the power stage?

The SYNC pin receives a synchronized signal from the secondary winding of the flyback transformer. Its falling edge forces the GATE signal to turn off precisely when the primary-side MOSFET turns on - ensuring the external N-channel MOSFET turns on only when secondary winding current has decayed to zero. This achieves zero-current switching, reducing voltage spikes, EMI, and MOSFET conduction losses.

Is thermal protection active during startup, and what is its response behavior?

Yes - thermal protection activates immediately upon power-up. When junction temperature exceeds 150°C (rising edge), the IC shuts down and latches off. A 25°C hysteresis ensures the device remains off until temperature drops below 125°C, preventing thermal runaway during initial surge or inadequate heatsinking. The ISET/FAULT pin goes low during thermal shutdown.