onsemi FAN5307S15X

Overview

FAN5307S15X from Fairchild Semiconductor is a high-efficiency, synchronous step-down DC-DC converter delivering up to 300mA output current with fixed 1.5V output, 2.5V–5.5V input range, and 1MHz PWM switching frequency. It operates in both pulse-width modulation (PWM) and power-save (PFM) modes, achieving 95% peak efficiency and 15µA quiescent current for battery-powered portable electronics.

For engineers reviewing the FAN5307S15X datasheet, pinout, applications, or equivalent options, key selection considerations include its 5-lead SOT-23 package, fixed 1.5V output, dynamic voltage positioning for transient headroom, 100% duty-cycle low-dropout capability, and integrated soft-start circuitry.

Technical Context

The FAN5307S15X implements a current-mode PFM/PWM hybrid control architecture: at light loads (<80mA), it enters variable-frequency pulse-skipping (PFM) mode with 0.8% dynamic output voltage positioning above nominal to improve load transient response; at moderate-to-heavy loads, it switches to fixed 1MHz PWM operation with cycle-by-cycle current limiting (520mA typical).

It integrates synchronous P-channel and N-channel MOSFETs with on-resistances of 670–850mΩ (P-ch) and 530–660mΩ (N-ch) at 2.5V V_GS, supports 100% duty-cycle operation for near-LDO behavior, and features digital soft-start (four-step current ramp, ~500µs startup time with 10µF C_OUT and 200mA load).

Key Specifications

Pinout & Package

Package: 5-lead SOT-23 (JEDEC MO-178, variation AA), footprint dimensions 2.80 × 2.90 × 1.45 mm max, with exposed pad not electrically connected.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar step-down DC-DC converter applications.

Compared with TPS62231DRYR and RT8059GJ6, the FAN5307S15X uniquely combines 100% duty-cycle operation, dynamic voltage positioning, and 15µA quiescent current in a mature, widely available SOT-23 package-making it optimal for cost-sensitive, battery-life-critical portable designs where layout simplicity and transient robustness are prioritized over minimal footprint.

Availability

FAN5307S15X is available at Aetrix Electronics and suitable for pocket PCs, cell phones, and digital cameras requiring stable component supply with RoHS-compliant tape-and-reel packaging and guaranteed long-term continuity.

Supply support for FAN5307S15X 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

Fairchild Semiconductor was a U.S.-based semiconductor company specializing in power management, analog, and discrete solutions before its acquisition by ON Semiconductor in 2016; its legacy products remain widely deployed in industrial and consumer systems.

The FAN5307 series was designed specifically for high-efficiency, low-quiescent-current power conversion in space-constrained, battery-operated portable electronics - emphasizing thermal performance, transient response, and ease of integration without external compensation.

FAQ

What is the output voltage tolerance of the FAN5307S15X over temperature and load?

The FAN5307S15X delivers a fixed 1.5V output with ±4% accuracy across the full operating ambient temperature range (-40°C to +85°C) and full load range (0–300mA). This specification is verified per the Electrical Characteristics table in the Rev. 1.0.5 datasheet, where V_OUT accuracy is explicitly tested at VIN = 2.5–5.5V and I_OUT = 0–300mA. The FAN5307S15X achieves this stability using an internal precision bandgap reference and trimmed feedback network.

Does the FAN5307S15X require external compensation components?

No, the FAN5307S15X is internally compensated and requires no external compensation components. Its current-mode control architecture with built-in slope compensation and fixed-frequency PWM eliminates the need for external RC networks or type-II/III compensators. The FAN5307S15X only requires standard input (4.7µF) and output (10µF) ceramic capacitors plus a 10µH inductor for full operation - simplifying design and reducing BOM count.

How does the FAN5307S15X handle load transients from 10mA to 300mA?

The FAN5307S15X maintains output regulation during rapid load steps using current-mode control and dynamic voltage positioning: in PFM mode, the output is pre-biased +0.8% above 1.5V to provide headroom, and the error amplifier responds within 10µs to correct droop. Test data (Figure 6 and Figure 9) shows <35mV undershoot for 100mA/µs transients. The FAN5307S15X sustains this performance across its full input range (2.5–5.5V) without external adjustments.

Can the FAN5307S15X operate with an input voltage below 2.5V?

No, the FAN5307S15X has a specified minimum input voltage of 2.5V per Absolute Maximum and Recommended Operating Conditions tables. Below 2.5V, the internal P-channel MOSFET cannot maintain sufficient gate drive, causing regulation loss and potential dropout failure. While 100% duty-cycle operation extends usability near V_OUT, the FAN5307S15X will cease switching and enter undervoltage lockout if VIN drops below 2.3V (typical UVLO threshold).

Is the FAN5307S15X pin-compatible with other variants in the FAN5307 family?

Yes, the FAN5307S15X shares identical 5-lead SOT-23 pinout and footprint with FAN5307S18X and FAN5307SX (adjustable version), including VIN, GND, EN, FB, and LX assignments. However, the FB pin function differs: for fixed-output versions like FAN5307S15X, FB is internally connected to the 1.5V reference and must be shorted to VOUT; for adjustable versions, FB connects to an external resistor divider. No PCB changes are needed when substituting within the SOT-23 fixed-output group.