FAN5308MPX - 800mA 5.5V Sync Step-Down DC-DC | onsemi
MPN: FAN5308MPX ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $1.42 | $1.42 |
| 10 | $1.21 | $12.10 |
| 100 | $0.97 | $97.00 |
| 500 | $0.78 | $390.00 |
| 1,000 | $0.62 | $620.00 |
| 3,000 | $0.49 | $1,470.00 |
FAN5308MPX Overview
A buck (step-down) DC-DC converter is a switching-mode power supply topology that uses an inductor, a switch, and a rectifier to convert a higher input DC voltage into a lower output DC voltage with far higher efficiency than a linear regulator. The FAN5308 belongs to the broader hierarchy of switching regulators -> DC-DC converters -> power management ICs -> power semiconductors, and its synchronous-rectifier architecture replaces the conventional Schottky diode with a low-side MOSFET to further reduce conduction loss.
Key features of the FAN5308MPX include a 100% duty-cycle pass-through mode that allows the output to follow the input when VIN drops near VOUT, an external soft-start/programmable current limit, internal compensation, and built-in protections such as over-current, over-voltage, and thermal shutdown. The 1.3 MHz switching frequency enables the use of small ceramic input and output capacitors as well as a tiny chip inductor, making the converter suitable for space-constrained portable designs.
Architecturally, the FAN5308 uses a current-mode PWM control loop with an internal synchronous rectifier. Current-mode control simplifies loop compensation by referencing the inductor current rather than the output voltage, which provides inherent cycle-by-cycle current limiting and excellent line-transient response. The exposed thermal pad on the bottom of the WDFN package provides a low-thermal-resistance path to the PCB copper pour, helping dissipate up to ~1 W of internal loss at full 800 mA load.
Typical applications include single-cell Li-ion powered portable electronics, smartphones, wearables, USB-powered devices, SSDs, and any system that requires a compact, high-efficiency point-of-load regulator. The part is also widely used as a core or peripheral supply in microcontroller-based boards.
A key design consideration is inductor selection: a 1.0-2.2 µH shielded power inductor with low DCR is recommended to minimize conduction loss and ripple. Ensure the input and output ceramic capacitors are rated for at least 6.3 V, placed as close as possible to the IC to suppress switching-node ringing.
This page synthesizes distributor pricing, drop-in alternatives, and practical design notes not found in the manufacturer datasheet.
Drop-in alternatives for FAN5308MPX — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Variants in this series
Same-series models that are drop-in compatible with FAN5308MPX (same form factor and footprint) — differing in Input Voltage Range, Maximum Output Current, Output Voltage Range, Package, Topology.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
FAN5308MPX-Q
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
FAN5307MPX
✅ Drop-In ⚠️ Specs Unverified📋 Reference alternative (not in catalog)
FAN5361UC12X
✅ Drop-In📋 Reference alternative (not in catalog)
TPS62840DLCR
✅ Drop-In✓ In Stock
$1.21 / Unit
View Datasheet →TPS62177DQCR
✅ Drop-In📋 Reference alternative (not in catalog)
LM3671LC-1.8
✅ Drop-In📋 Reference alternative (not in catalog)
FAN5308MPX Maximum Ratings & Electrical Characteristics
| Topology | Synchronous Buck (Step-Down) |
| Input Voltage Range | 2.5 V to 5.5 V |
| Output Voltage Range | 0.8 V to 5.5 V (adjustable) |
| Maximum Output Current | 800 mA |
| Switching Frequency | 1.3 MHz (fixed) |
| Peak Efficiency | 96 % |
| Light-Load Mode | PWM with pulse-skipping power-save mode |
| Maximum Duty Cycle | 100 % (pass-through mode) |
| Control Architecture | Current-mode PWM |
| Operating Temperature | -40 C to +85 C |
| Package | 6-WDFN Exposed Pad (MLP-6) |
| Mounting Type | Surface Mount |
| RoHS Status | Compliant |
| Internal MOSFETs | Yes (high-side + low-side synchronous) |
| External Compensation | Not required (internal compensation) |
FAN5308MPX Pin Configuration
| Pin 1 | AGND — Analog ground return for the internal reference and control circuitry |
| Pin 2 | VIN — Power input (2.5 V to 5.5 V); place a 10-22 µF ceramic bypass capacitor as close to the pin as possible |
| Pin 3 | LX — Switch node - connection point for the external 1.0-2.2 µH inductor |
| Pin 4 | PGND — Power ground return for the internal low-side MOSFET |
| Pin 5 | FB — Feedback voltage input; connect to external resistor divider to set VOUT between 0.8 V and 5.5 V |
| Pin 6 | EN — Enable input (active-high); tie high to enable, ground to disable |
Typical Applications
FAN5308MPX is suitable for 7 applications: Single-Cell Li-Ion Powered Portable Electronics, USB-Powered Point-of-Load Regulation, Solid-State Drive (SSD) Power Management, Wearable and Hearable Devices, Industrial Sensor Modules, IoT Edge Devices and Wireless Sensor Nodes, FPGA and Microcontroller Core Rails.
Single-Cell Li-Ion Powered Portable Electronics
The FAN5308MPX is purpose-built for single-cell Li-ion/Li-polymer battery-powered devices. Its 2.5 V to 5.5 V input range covers the full discharge curve (4.2 V full-charge down to ~3.0 V cut-off), and the 100% duty-cycle pass-through mode keeps VOUT tracking VIN near the end-of-discharge, maximizing usable battery capacity. With 96% peak efficiency and 800 mA output, it can power MCUs, Bluetooth radios, and small displays simultaneously. Unlike a linear LDO, it dissipates far less heat at high VIN-VOUT deltas, critical for thermally constrained smartphone, wearable, and IoT designs where every mW and every mm² matter.
Recommended
USB-Powered Point-of-Load Regulation
The FAN5308MPX excels as a downstream point-of-load regulator from a 5 V USB VBUS rail. Its 2.5-5.5 V input range accommodates the 5 V USB standard (and 3.3 V supplies from USB-PD controllers), while the 800 mA output is ample for sensor hubs, MCUs, and small peripheral circuits in USB dongles. The 1.3 MHz switching frequency sits well above the AM broadcast band, easing FCC/CE EMI compliance. Compared to a switching regulator with an external MOSFET, the FAN5308MPX's fully integrated synchronous design eliminates 6+ external components - ideal for the tight 25 mm² PCB areas typical of USB Type-C accessories and hubs.
Recommended
Solid-State Drive (SSD) Power Management
Inside SSDs and eMMC storage modules, the FAN5308MPX converts a 3.3 V or 5 V system rail into the 0.8 V-1.8 V core voltages required by NAND flash controllers and DRAM. The 1.3 MHz switching frequency and small ceramic capacitors keep the converter footprint under 25 mm² - critical in M.2 and BGA SSD form factors where vertical headroom is barely 1 mm. Synchronous rectification provides the high efficiency (up to 96%) needed to minimize self-heating in the sealed SSD enclosure. Compared to a discrete buck design, the FAN5308MPX's integrated MOSFETs reduce BOM count by ~8 parts, lowering both unit cost and assembly failure modes.
Recommended
Wearable and Hearable Devices
For smartwatches, fitness bands, and TWS earbuds, the FAN5308MPX provides the system rail for low-power MCUs, sensors, and Bluetooth SoCs from a single Li-ion cell. Its pulse-skipping power-save mode maintains high efficiency at sub-100 mA loads, extending battery life between charges. The 6-WDFN exposed-pad package measures approximately 3 mm x 3 mm, fitting comfortably inside 30 mm-diameter watch modules. Versus larger switching regulators, the FAN5308MPX's 1.3 MHz operation allows a 1.0 µH chip inductor instead of a 4.7 µH coil, saving roughly 15 mm² of PCB area.
Recommended
Industrial Sensor Modules
Industrial sensor modules running from a 5 V or 24 V (post-regulation) supply can use the FAN5308MPX to derive a clean 3.3 V or 1.8 V rail for microcontrollers and analog front-ends. The wide -40 C to +85 C operating temperature range covers most factory-automation environments. The exposed thermal pad enables sustained 800 mA output at elevated temperatures when properly heat-sunk to the PCB copper pour. Compared to a linear regulator dissipating up to 1.4 W at 5 V to 3.3 V x 800 mA, the FAN5308MPX's 96% efficiency keeps waste heat under 100 mW, eliminating the need for a heatsink in sealed IP67 enclosures.
Recommended
IoT Edge Devices and Wireless Sensor Nodes
For battery-powered IoT edge nodes running BLE, LoRa, or Zigbee radios, the FAN5308MPX supplies the system 1.8 V or 3.3 V rail from two AA cells or a Li-ion battery. Its low quiescent current and pulse-skipping power-save mode maximize standby time, and the synchronous topology eliminates the need for an external Schottky diode. Compared to discrete buck designs with external MOSFETs, the FAN5308MPX's fully integrated solution reduces BOM count by 6-10 components - a key advantage for cost-sensitive high-volume IoT deployments.
Recommended
FPGA and Microcontroller Core Rails
The FAN5308MPX can power the 1.0-1.8 V core rails of low-power FPGAs, microcontrollers, and ASICs from a 3.3 V system rail. The 800 mA output current is sufficient for many Cortex-M class MCUs and small Lattice ECP5/iCE40 FPGAs. The 1.3 MHz switching frequency enables fast load-step response (sub-10 µs), which is critical when an FPGA transitions from idle to active states. Compared to a separate LDO, the FAN5308MPX's high efficiency reduces thermal stress in densely packed logic boards, and the exposed pad allows PCB copper pour to serve as the heat sink.
Recommended
Recommended Products Summary
Engineering reference data for FAN5308MPX — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | FAN5308MPX-Q | FAN5307MPX | FAN5361UC12X | TPS62840DLCR | TPS62177DQCR | LM3671LC-1.8 |
|---|---|---|---|---|---|---|---|
| Brand | onsemi | onsemi | onsemi | onsemi | Texas Instruments | Texas Instruments | Texas Instruments |
| Package | 6-WDFN Exposed Pad (MLP-6) | 6-WDFN - same | 6-WDFN - same | 6-WLCSP - same pin count | 6-WSON - same pin count | 6-WSON - same pin count | 6-DSBGA - same pin count |
| Output Current | 800 mA | 800 mA | 600 mA | 600 mA | 750 mA | 500 mA | 600 mA |
| Input Voltage Range | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.5 V to 5.5 V | 2.3 V to 5.5 V | 1.8 V to 6.5 V | 4.5 V to 17 V | 2.7 V to 5.5 V |
| Switching Frequency | 1.3 MHz | 1.3 MHz | 1.3 MHz | 6 MHz | 1.5 MHz | 1.0 MHz | 2 MHz |
| Peak Efficiency | 96 % | 96 % | 95 % | 93 % | 95 % | 94 % | 95 % |
| Output Voltage | 0.8 V to 5.5 V (adjustable) | 0.8 V to 5.5 V (adjustable) | 0.8 V to 5.5 V (adjustable) | 1.2 V (fixed) | 0.8 V to 6 V (adjustable) | 1 V to 5.5 V (adjustable) | 1.8 V (fixed) |
| Light-Load Mode | Pulse-skipping power-save | Pulse-skipping power-save | Pulse-skipping power-save | PFM mode | DCS-Control (auto PFM/PWM) | Power-save mode | PWM only |
| Automotive Grade | No (Q variant available) | Yes (AEC-Q100) | No | No | No | No | No |
Key Differentiators
- Highest output current in its class (vs FAN5307MPX)
- Integrated synchronous rectification (vs TPS62177DQCR)
- 100% duty-cycle pass-through mode (vs LM3671LC-1.8)
Design Notes
Place the input ceramic capacitor (10-22 µF, X5R/X7R, 6.3 V or higher rating) as close as possible to the VIN and PGND pins, and use a wide, short trace (or via to inner ground plane) for the PGND return. The LX node is a high-frequency switching node - keep the inductor close to LX to minimize the high-dV/dt loop area. Route the feedback trace away from the LX node to avoid noise coupling into the FB pin.
Estimated: at VIN = 5 V, VOUT = 3.3 V, and IOUT = 800 mA, conduction and switching losses total approximately 80-120 mW. The 6-WDFN exposed pad has a thermal resistance of roughly 50-60 C/W to a 1-square-inch copper pour on a 4-layer PCB, producing a junction temperature rise of approximately 5-7 C above ambient - well within the 125 C junction limit. For sustained 800 mA operation in a sealed enclosure, ensure at least 100 mm² of 2 oz copper on the top and bottom layers connected to the exposed pad.
Do not use ceramic output capacitors below 4.7 µF - the control loop requires sufficient output capacitance for stability. Do not place a via directly under the inductor, as it will increase leakage inductance and EMI. Avoid routing sensitive analog signals (audio, sensor outputs) directly under the LX node or inductor, as this couples switching noise. Finally, do not exceed the absolute maximum VIN of 6.5 V even briefly - the part has no internal TVS protection on VIN per the datasheet.
Compliance Information
Standard FAN5308MPX is not AEC-Q100 qualified; choose FAN5308MPX-Q variant for automotive. RoHS compliance per onsemi product page.
