onsemi FAN21SV04MPX

Overview

FAN21SV04MPX from onsemi (formerly Fairchild) is a fully integrated synchronous buck regulator delivering up to 4 A output current with input voltage range of 3.0 V to 24 V, output voltage programmable from 0.8 V to 80% VIN, and peak efficiency exceeding 94%. It integrates high- and low-side MOSFETs, gate drivers, internal 5 V bias regulator, bootstrap diode, and protection circuitry in a single 5 × 6 mm MLP package - designed for point-of-load regulation in space-constrained computing and telecom systems.

For engineers reviewing the FAN21SV04MPX datasheet, pinout, applications, or equivalent options, key selection considerations include its programmable 200–600 kHz switching frequency, master/slave clock synchronization capability, external compensation flexibility, pre-bias startup support, and comprehensive fault protections including over-current, over-voltage, under-voltage, and thermal shutdown.

Technical Context

The FAN21SV04MPX employs summing-mode PWM control with cycle-by-cycle current limiting, using an internally generated ramp combined with amplified current-sense feedback. Its error amplifier drives COMP with external compensation network, enabling stable loop tuning across load and line variations.

It features dual-supply operation: VIN_Reg ≥ 6.5 V enables single-supply mode via internal 5 V regulator; below 6.5 V, VIN_Reg must be supplied externally. The device supports both free-running and synchronized operation via bi-directional CLK pin, with 180° phase shift in master-slave configurations for multi-phase interleaving.

Key Specifications

Pinout & Package

Package: Molded Leadless Package (MLP), 5 × 6 mm, 25-pin with 3 thermal pads (P1–P3). Thermally enhanced bottom-exposed copper pads improve heat transfer to PCB ground plane.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2315DJ-LF-Z and TPS544B25RJER, the FAN21SV04MPX provides higher current capability than the former and simpler analog control than the latter, making it optimal for cost-sensitive, high-density analog PoL designs requiring robust fault handling and flexible frequency configuration without digital overhead.

Availability

FAN21SV04MPX is available at Aetrix Electronics and suitable for server VRMs, telecom point-of-load regulators, and gaming console SoC supplies requiring stable component supply, long-term lifecycle support, and consistent parametric performance across production batches.

Supply support for FAN21SV04MPX 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

onsemi (formerly Fairchild Semiconductor) is a global semiconductor supplier specializing in energy-efficient power management, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The FAN21SV04MPX belongs to the TinyBuck™ family of integrated synchronous buck regulators, engineered specifically for high-current, space-constrained point-of-load applications where minimal external components, thermal efficiency, and robust protection are mandatory.

FAQ

What is the operating temperature range for the FAN21SV04MPX?

The FAN21SV04MPX has an ambient operating temperature range of –10°C to +85°C, as specified in the ordering information for this variant. Its junction temperature is rated up to +125°C, with thermal shutdown activating at +155°C and hysteresis of +30°C. The device uses a thermally enhanced MLP package with θJ-PCB = 35 °C/W on a standard 4-layer PCB, enabling reliable operation at full 4 A load within this ambient range when properly laid out.

Does the FAN21SV04MPX support startup on a pre-biased output?

Yes, the FAN21SV04MPX supports startup on a pre-biased output. During soft-start, the low-side MOSFET remains disabled until the internal soft-start ramp reaches ~95% of the 0.8 V reference (~0.76 V), preventing discharge of the pre-biased rail. This behavior is explicitly confirmed in the Application Information section and validated in Figure 26 ("Startup on Pre-Bias") of the datasheet, making FAN21SV04MPX suitable for hot-swap and multi-rail sequencing applications.

How is the switching frequency programmed on the FAN21SV04MPX?

The switching frequency of the FAN21SV04MPX is programmed using an external resistor (RT) connected from the RT pin (P18) to AGND for master mode (200–600 kHz), or to 5V_Reg for slave mode. For example, RT = 50 kΩ yields ~300 kHz, and RT = 24 kΩ yields ~600 kHz in master mode. In slave mode, the device synchronizes to an external clock on the CLK pin with ±15% frequency tolerance relative to master mode, enabling precise multi-phase interleaving.

What protections does the FAN21SV04MPX include?

The FAN21SV04MPX includes over-current protection (5.5–7.5 A, cycle-by-cycle), over-voltage protection (110–120% VOUT), under-voltage protection (68–78% VOUT), thermal shutdown (+155°C), and fault latch with auto-restart capability. All protections are active after soft-start completion (T1.0), except over-current which is enabled earlier. The EN pin controls restart behavior: open enables immediate restart; pulled to GND disables; biased via resistor enables latched-off mode - configurations detailed in Table 1 of the datasheet.

Can the FAN21SV04MPX operate with input voltage below 6.5 V?

Yes, the FAN21SV04MPX can operate with input voltage below 6.5 V, but only in dual-supply mode: VIN (P2, P3–P5) may be as low as 3.0 V, while VIN_Reg (P2) must be supplied externally with a separate ≥6.5 V source. The internal 5 V regulator requires VIN_Reg ≥ 6.5 V to function; if VIN < 6.5 V, VIN_Reg cannot be derived from VIN and must be provided independently - as clarified in the "Internal Regulator" section and Figure 10/11 application circuits.