onsemi FAN8303MX

Overview

FAN8303MX from ON Semiconductor is a monolithic non-synchronous step-down (buck) DC/DC regulator with an integrated 0.22 Ω high-side MOSFET, delivering up to 2 A continuous output current across a 5 V to 23 V input range and supporting adjustable output voltages from 0.6 V to 20 V. It operates at a fixed 370 kHz switching frequency, achieves up to 90% efficiency, and features cycle-by-cycle over-current protection - ideal for auxiliary power supplies in consumer set-top boxes and DSL/cable modems.

For engineers reviewing the FAN8303MX datasheet, pinout, applications, or equivalent options, key selection criteria include its internal MOSFET R_DS(on), thermal shutdown threshold (155 °C), soft-start programmability via external capacitor, stable operation with low-ESR ceramic output capacitors, and compatibility with standard 8-pin SOIC PCB footprints.

Technical Context

The FAN8303MX implements peak current-mode PWM control with internal slope compensation to ensure stability at duty cycles above 50%. Its feedback reference voltage is tightly regulated at 0.60 V ±20 mV, and it uses an internal transconductance error amplifier (380 µA/V) with 400 V/V gain for loop control.

Fault protection includes cycle-by-cycle current limiting (3.5 A peak inductor current), frequency foldback during short-circuit (reducing to ~45 kHz), and thermal shutdown with hysteresis. The IC supports enable-controlled startup and programmable soft-start timing via an external capacitor on the SS pin.

Key Specifications

Pinout & Package

Package: 8-pin SOIC (Small Outline Integrated Circuit), 3.9 mm × 4.9 mm body, 1.27 mm pitch, JEDEC MS-012AC compliant. Thermal resistance θ_JA = 105 °C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP1584EN-LF-Z and LM2678SD-ADJ/NOPB, the FAN8303MX offers superior integration (internal bootstrap diode, slope compensation, soft-start pin) and tighter feedback reference (0.60 V ±20 mV), making it optimal for cost-sensitive, space-constrained consumer power supplies requiring rapid design completion.

Availability

FAN8303MX is available at Aetrix Electronics and suitable for set-top box power rails, DSL/cable modem auxiliary supplies, and distributed power systems requiring stable component supply, consistent parametric performance, and long-term lifecycle support.

Supply support for FAN8303MX 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

ON Semiconductor (formerly Fairchild Semiconductor) is a global semiconductor supplier focused on energy-efficient electronics, with leadership in power management, analog, and sensor technologies.

The FAN8303MX belongs to ON Semiconductor's legacy Fairchild analog power IC portfolio, designed specifically for cost-optimized, high-efficiency non-synchronous buck conversion in consumer and broadband infrastructure applications.

FAQ

What is the maximum output current capability of the FAN8303MX under typical operating conditions?

The FAN8303MX delivers up to 2 A continuous output current when operated within its recommended conditions: VIN = 12 V, TA = 25 °C, with proper PCB layout, thermal vias, and 15 µH inductor. Peak inductor current is rated at 3.5 A, but sustained 2 A output requires adequate heatsinking and airflow - especially near the upper end of the 5–23 V input range where duty cycle increases.

Does the FAN8303MX require an external bootstrap diode, or is it integrated?

The FAN8303MX integrates a synchronous bootstrap diode internally. No external diode is required between the BS and SW pins - only a 10 nF ceramic capacitor (CBS) is needed to maintain gate drive voltage for the high-side MOSFET. This integration reduces component count and improves reliability compared to controllers requiring discrete bootstrap solutions.

Can the FAN8303MX operate with an input voltage as low as 5 V, and what are the limitations?

Yes, the FAN8303MX supports VIN down to 5 V (minimum specified). However, at low input voltage, maximum achievable output current decreases due to duty cycle constraints and reduced headroom for the high-side switch. Figure 15 in the datasheet shows that at VIN = 5 V and VOUT = 3.3 V (66% duty), the allowable peak current drops below 2 A - designers must verify load capability using the duty-ratio vs. current-limited-level curve.

How is output voltage programmed on the FAN8303MX, and what tolerance should be expected?

Output voltage is programmed using a resistor divider from VOUT to GND, connected to the FB pin. The formula is VOUT = 0.6 V × (1 + R2/R3), where R2 connects to VOUT and R3 to GND. With a 0.60 V ±20 mV reference and 1% resistors, total output tolerance is typically ±2.5% - dominated by reference accuracy and resistor matching. Layout parasitics on the FB trace can introduce additional error if not routed away from noisy nodes like SW.

What protection features does the FAN8303MX include, and how do they behave during fault conditions?

The FAN8303MX includes cycle-by-cycle over-current protection (limiting peak inductor current to ~3.5 A), thermal shutdown at 155 °C with hysteresis, and frequency foldback during output short-circuit (reducing oscillator frequency to ~45 kHz). During a hard short, the IC enters hiccup mode - cycling between shutdown and restart - preventing thermal runaway while maintaining detectability for system-level fault logging.