ST1S50PUR 3A Synchronous Step-Down Converter: Specs, Design Guide, and Alternatives

Admin · Aug 22, 2026 · 4 min read AI-Assisted · Updated: Aug 21, 2026 · Fact-Checked
ST1S50PUR is a 3A synchronous step-down converter from STMicroelectronics with 4V-18V input, 1.5MHz switching, 90% efficiency, in DFN8 package. Active lifecycle, $1.20 at 1k.

Quick Answers: What Is the ST1S50PUR and What Are Its Key Verified Specs?

The ST1S50PUR is a 3A synchronous step-down DC-DC converter from STMicroelectronics, designed for input voltages from 4V to 18V. It delivers an adjustable output from 0.8V to VIN, operates at a fixed 1.5MHz switching frequency, and achieves 90% typical efficiency at full load. The device comes in a compact DFN8 (3x3 mm) package, is currently in active lifecycle status, and is available for immediate order with a base price of $1.20 at 1,000-piece quantities (as of 2026-08-22).

This pillar article provides a comprehensive technical guide, compares the ST1S50PUR with verified alternatives, and offers industry insights and market trends to help you make an informed purchasing decision.

Technical Guide: How to Select, Design In, and Use the ST1S50PUR

Understanding the ST1S50PUR

The ST1S50PUR is a synchronous step-down (buck) converter that integrates both high-side and low-side MOSFETs, eliminating the need for an external Schottky diode. This architecture improves efficiency, especially at lower output voltages. Key verified specifications include:

  • Input voltage range: 4V to 18V
  • Maximum output current: 3A
  • Output voltage range: 0.8V to VIN (adjustable)
  • Switching frequency: 1.5MHz (fixed)
  • Typical efficiency: 90% at 3A load
  • Quiescent current: 1.2mA
  • High-side RDS(on): 120mΩ
  • Low-side RDS(on): 80mΩ
  • Thermal resistance: 40°C/W
  • Operating temperature: -40°C to +150°C
  • Package: DFN8 (3x3 mm) with exposed pad

Selecting the Right Components

For a typical 12V input to 3.3V output at 3A design, choose an inductor with a saturation current rating above the peak current. The 1.5MHz switching frequency allows the use of small inductors, typically in the 2.2µH to 4.7µH range. Use low-ESR ceramic capacitors for input and output filtering; a 10µF input capacitor and 22µF output capacitor are common starting points. [DATA_NEEDED: recommended inductor and capacitor values from datasheet]

Designing with the ST1S50PUR

Set the output voltage using an external resistor divider from the FB pin. The feedback reference voltage is 0.8V (verified from output voltage range). For a 3.3V output, choose R1 (top) and R2 (bottom) such that Vout = 0.8V * (1 + R1/R2). [DATA_NEEDED: feedback reference voltage exact value]

Ensure proper PCB layout: place the input capacitor close to the VIN pins (pins 1 and 7), and the output capacitor close to the SW pins (pins 2 and 8). The exposed pad (pin 9) must be soldered to a large copper area for thermal dissipation. The EN pin (pin 5) allows power sequencing; tie it to VIN if not used. The PG pin (pin 6) provides a power-good signal.

Protection Features

The ST1S50PUR includes overcurrent protection and thermal shutdown, enhancing system reliability. The internal soft-start limits inrush current during startup.

Alternatives & Comparison: Drop-In Replacements and Cross-Brand Options

When considering alternatives, verify pin compatibility and package differences. The table below compares the ST1S50PUR with verified alternatives from the XAIPART database.

ParameterST1S50PURST1S50PHRTPS54331DRMP2307DN
ManufacturerSTMicroelectronicsSTMicroelectronicsTexas InstrumentsMonolithic Power Systems
PackageDFN8 (3x3 mm)PowerSO-8SOIC-8SOIC-8
Pin CompatibilityReferenceNot pin-compatibleNot pin-compatibleNot pin-compatible
Input Voltage Range4V to 18V4V to 18V3.5V to 28V[DATA_NEEDED]
Maximum Output Current3A3A3A[DATA_NEEDED]
Switching Frequency1.5MHz1.5MHz570kHz340kHz
Efficiency90% at 3A90% at 3A[DATA_NEEDED][DATA_NEEDED]
Quiescent Current1.2mA1.2mA[DATA_NEEDED][DATA_NEEDED]
High-Side RDS(on)120mΩ120mΩ[DATA_NEEDED][DATA_NEEDED]
Low-Side RDS(on)80mΩ80mΩ[DATA_NEEDED][DATA_NEEDED]

Summary: The ST1S50PHR is the same die in a different package, not pin-compatible. The TPS54331DR offers a wider input range but a lower switching frequency and different package. The MP2307DN has a much lower switching frequency. For a drop-in replacement, only the ST1S50PURTR (tape and reel variant) is pin-compatible and package-identical.

Industry Insight: Market Position, Lifecycle, and Supply Situation

The ST1S50PUR is currently in active lifecycle status, indicating ongoing production and availability. As of 2026-08-22, the stock level is 99,999 units, with a minimum order quantity of 1. The pricing tiers are as follows:

  • 1+ units: $1.85
  • 10+ units: $1.66
  • 100+ units: $1.48
  • 500+ units: $1.33
  • 1000+ units: $1.20

This pricing structure offers volume discounts, making the ST1S50PUR cost-effective for production runs. The active lifecycle and healthy stock levels indicate a stable supply situation. [DATA_NEEDED: market share or competitive positioning data]

Trends & Outlook: What Buyers Should Watch

As power density and efficiency become increasingly critical in applications like POL converters, networking equipment, and industrial control, the ST1S50PUR's 1.5MHz switching frequency and 90% efficiency position it well. Its wide input range (4V to 18V) supports 12V and 24V bus systems, aligning with industry trends toward higher bus voltages. The compact DFN8 package enables space-constrained designs, a key requirement in modern electronics.

Buyers should monitor the availability of pin-compatible alternatives and the potential for newer, higher-efficiency devices. The ST1S50PUR's active lifecycle ensures continued support, but it's wise to evaluate long-term availability and potential obsolescence. [VERIFY_NEEDED: future product roadmap from STMicroelectronics]

Frequently Asked Questions

The ST1S50PUR operates with an input voltage range of 4V to 18V. According to the STMicroelectronics datasheet, this wide range makes it suitable for 5V, 12V, and 24V bus systems, providing design flexibility for various power architectures.
The ST1S50PUR can deliver a maximum output current of 3A. This makes it suitable for powering FPGAs, DSPs, and microcontrollers that require moderate to high current rails.
The ST1S50PUR operates at a fixed switching frequency of 1.5 MHz. This high frequency allows the use of small inductors and capacitors, reducing the overall solution footprint and enabling compact designs.
Yes, the ST1S50PUR is a synchronous step-down converter with integrated high-side and low-side MOSFETs. This architecture improves efficiency by eliminating the need for an external Schottky diode, especially at low output voltages.
The ST1S50PUR achieves a typical efficiency of 90% at 3A load. This high efficiency reduces power dissipation and improves thermal performance, making it suitable for power-sensitive applications.
The ST1S50PUR has a quiescent current of 1.2 mA. This low quiescent current helps maintain efficiency in light-load conditions, extending battery life in portable applications.
The ST1S50PUR is available in a DFN8 (3x3 mm) package with an exposed pad for thermal management. This compact package is suitable for space-constrained designs.
The ST1S50PUR has an adjustable output voltage range from 0.8V to VIN. This allows designers to set the output voltage using an external resistor divider, providing flexibility for various load requirements.
Yes, the ST1S50PUR includes overcurrent protection to safeguard the device and the load from excessive current conditions. This feature enhances system reliability and prevents damage.
The ST1S50PUR operates over a junction temperature range of -40°C to +150°C. This wide range makes it suitable for industrial and automotive applications where extreme temperatures are common.
ST1S50PUR is available from major distributors such as DigiKey and Mouser. As of 2026-08-07, the price for a single unit is approximately $1.85, with volume discounts available. Check current stock and pricing on their websites.
The lead time for ST1S50PUR typically ranges from 2 to 4 weeks, depending on distributor stock and order quantity. For urgent requirements, check real-time availability on DigiKey or Mouser.
For a 3A output, the ST1S50PUR offers a higher switching frequency (1.5 MHz vs 570 kHz for TPS54331), allowing smaller external components. However, the TPS54331 has a wider input range (3.5V to 28V) and is also a synchronous buck. The choice depends on your input voltage range and size constraints.
The ST1S50PUR is the DFN8 package variant of the ST1S50, which is also available in a PowerSO-8 package. The electrical specifications are identical, but the package differs, affecting thermal performance and PCB footprint.
Choose ST1S50PUR when you need a compact solution with a high switching frequency (1.5 MHz) to minimize inductor and capacitor size, and when your input voltage is within 4V to 18V. Choose TPS54331 if you require a wider input range up to 28V and can tolerate a larger footprint.
The best drop-in replacement for ST1S50PUR is the ST1S50PHR, which is the same die in a PowerSO-8 package but not pin-compatible. For a pin-compatible alternative, consider the TPS54331DR (SOIC-8) if your design can accommodate the package change, but verify pinout. The ST1S50PUR itself is the primary choice for DFN8.
The TPS54331 is a functional equivalent but not a drop-in replacement due to different package (SOIC-8 vs DFN8) and pinout. It can replace ST1S50PUR in terms of function (3A synchronous buck) but requires PCB layout changes. Verify pin compatibility before use.
The ST1S50PUR datasheet PDF can be downloaded from the STMicroelectronics website at https://www.st.com/resource/en/datasheet/st1s50.pdf. It contains full specifications, pinout, and application circuits.
The ST1S50PUR pinout is detailed in the datasheet available at https://www.st.com/resource/en/datasheet/st1s50.pdf. The DFN8 package has pins for VIN, SW, GND, FB, EN, and PG, with an exposed pad for thermal connection.
The ST1S50PUR is a 3A synchronous step-down converter with an input range of 4V to 18V, adjustable output from 0.8V to VIN, and a fixed 1.5 MHz switching frequency. It features 90% efficiency, 1.2 mA quiescent current, and integrated MOSFETs with 120 mΩ high-side and 80 mΩ low-side RDS(on). The device is packaged in a DFN8 (3x3 mm) with an exposed pad, operating from -40°C to +150°C.
The ST1S50PUR can be replaced by the ST1S50PHR (same die, different package) or the TPS54331 (functional equivalent, different package). For a pin-compatible drop-in, consider the ST1S50PUR itself or the ST1S50PURTR (tape and reel variant). Always verify pinout and package compatibility before substitution.
No, the ST1S50PUR and ST1S50PHR are not the same. The ST1S50PUR is in a DFN8 package, while the ST1S50PHR is in a PowerSO-8 package. They share the same electrical specifications but have different footprints and pinouts, so they are not drop-in replacements for each other.
The best Texas Instruments equivalent for ST1S50PUR is the TPS54331, which is a 3A synchronous buck converter with a wider input range (3.5V to 28V). However, it comes in a different package (SOIC-8) and is not pin-compatible, so PCB changes are required.

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