STMicroelectronics

ST1S40PUR - 3A, 4V to 18V Step-Down Converter | STMicroelectronics

Name: ST1S40PUR
Brand: STMicroelectronics
Price: 1.25 USD
Availability: InStock

MPN: ST1S40PUR ✓ Active

In Stock (99,999) Ships in 1-3 business days

0.8 V to VIN Vdss 3 A Id 45 C/W Rds(on) DFN6 (3x3 mm) Package 1.5 MHz Speed

$1.25 USD / Unit

MOQ: 1 |

Volume Pricing

Qty	Unit Price	Extended
1	$1.25	$1.25
10	$1.12	$11.20
100	$0.98	$98.00
500	$0.85	$425.00
1,000	$0.72	$720.00

ℹ️ All prices are in USD

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Drop-in alternatives for ST1S40PUR — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.

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ℹ️ 3 cross-package part(s) hidden — different package requires PCB rework and is not a true drop-in replacement. Contact us if you need cross-package suggestions.

ST1S40PUR Maximum Ratings & Electrical Characteristics

Output Type	Adjustable
Output Voltage Range	0.8 V to VIN
Maximum Output Current	3 A
Input Voltage Range	4 V to 18 V
Switching Frequency	1.5 MHz
Efficiency	90% (typical)
Quiescent Current	1.5 mA
Shutdown Current	1 uA (max)
Thermal Resistance	45 C/W
Operating Temperature	-40C to +150C
Package	DFN6 (3x3 mm)
Mounting Type	Surface Mount
MSL Level	1 (unlimited)
RoHS Status	Compliant
Enable Pin	Yes (active-high)

ST1S40PUR Pin Configuration

Pin 1	VIN — Input supply voltage
Pin 2	SW — Switch node output
Pin 3	GND — Ground
Pin 4	FB — Feedback voltage
Pin 5	EN — Enable (active high)
Pin 6	GND — Ground (exposed pad)

Safe Operating Area (SOA) & Thermal Characteristics

No official SOA curve available for this component. Always operate within absolute maximum ratings specified in the datasheet. Ensure adequate cooling and derate as needed.

Typical Applications

ST1S40PUR is suitable for 6 applications: Set-Top Box Power Supply, Networking Equipment, Industrial Control Systems, LCD TV Power Supply, FPGA and DSP Power, Distributed Power Systems.

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Set-Top Box Power Supply

The ST1S40PUR efficiently converts a 12V input to 3.3V or 1.8V rails for core logic, reducing heat and improving reliability. Its 1.5MHz switching frequency allows small external components, fitting the compact form factor of set-top boxes. The high efficiency minimizes power loss, which is critical in enclosed consumer electronics. The device's overcurrent and thermal protection ensure safe operation under varying load conditions. With a wide input range, it can handle voltage fluctuations from the AC-DC adapter. The enable pin allows power sequencing with other rails, ensuring proper startup of the system.

Recommended

ST1S40PHR (Same die, different package) TPS54331 (Competitor equivalent)

🌐

Networking Equipment

In networking equipment such as routers and switches, the ST1S40PUR provides a stable 3.3V or 1.8V rail for FPGAs and ASICs. Its high output current of 3A supports the power demands of high-performance processors. The 1.5MHz switching frequency reduces the size of the inductor and capacitors, saving PCB space in dense designs. The device's low quiescent current helps meet energy efficiency standards. The wide input range accommodates various system voltages, from 5V to 12V. The thermal pad in the DFN6 package aids heat dissipation, ensuring reliable operation in confined spaces.

Recommended

ST1S40PHR (Same die, different package) TPS54331 (Competitor equivalent)

🏭

Industrial Control Systems

The ST1S40PUR is suitable for industrial control systems that require a robust power supply from a 24V bus. Its input voltage range of 4V to 18V allows it to operate from a 12V or 24V supply with proper derating. The device's high efficiency reduces heat generation, which is important in industrial enclosures with limited airflow. The overcurrent protection and thermal shutdown ensure safe operation in harsh environments. The adjustable output voltage allows it to generate various rails needed by microcontrollers and sensors. The compact DFN6 package is ideal for space-constrained control boards.

Recommended

ST1S40PHR (Same die, different package) MP2307 (Competitor equivalent)

📺

LCD TV Power Supply

In LCD TVs, the ST1S40PUR converts the main 12V rail to lower voltages for the timing controller, T-con board, and other logic circuits. Its 3A output current can handle the peak currents of these circuits. The 1.5MHz switching frequency allows the use of small, low-profile inductors, which is beneficial for slim TV designs. The device's high efficiency reduces power consumption, contributing to energy star ratings. The enable pin allows the TV to power down the logic circuits in standby mode, reducing standby power. The thermal performance of the DFN6 package ensures reliable operation in the warm environment inside a TV.

Recommended

ST1S40PHR (Same die, different package) TPS54331 (Competitor equivalent)

🔧

FPGA and DSP Power

The ST1S40PUR is ideal for powering FPGAs and DSPs that require a 1.8V or 3.3V rail with high current. Its 3A output current can supply the core voltage of many mid-range FPGAs. The adjustable output voltage allows precise setting of the core voltage. The high switching frequency reduces the size of the output filter, which is important in dense PCB layouts. The device's fast transient response ensures stable operation during dynamic load changes. The enable pin allows power sequencing with other rails, which is critical for FPGA startup.

Recommended

ST1S40PHR (Same die, different package) TPS54331 (Competitor equivalent)

⚡

Distributed Power Systems

The ST1S40PUR is used in distributed power systems where a central 12V bus is converted to various lower voltages at the point of load. Its wide input range and high efficiency make it suitable for this role. The device's small footprint allows it to be placed close to the load, reducing I2R losses in the PCB traces. The 1.5MHz switching frequency enables the use of small inductors, which is beneficial in multi-rail systems. The overcurrent protection prevents damage to the load in case of a fault. The enable pin allows individual rails to be powered up or down as needed.

Recommended

ST1S40PHR (Same die, different package) MP2307 (Competitor equivalent)

Recommended Products Summary

ST1S40PHR Same die, different package Used in: Set-Top Box Power Supply, Networking Equipment, Industrial Control Systems, LCD TV Power Supply, FPGA and DSP Power, Distributed Power Systems TPS54331 Competitor equivalent Used in: Set-Top Box Power Supply, Networking Equipment, LCD TV Power Supply, FPGA and DSP Power MP2307 Competitor equivalent Used in: Industrial Control Systems, Distributed Power Systems

What is the input voltage range of ST1S40PUR?

The ST1S40PUR operates from an input voltage range of 4V to 18V. According to the STMicroelectronics datasheet, this wide range allows it to be used in 5V, 12V, and 24V systems with appropriate derating.

What is the maximum output current of ST1S40PUR?

The ST1S40PUR can deliver up to 3A of continuous output current. This makes it suitable for powering FPGAs, DSPs, and microprocessors that require high current at low voltages.

What is the switching frequency of ST1S40PUR?

The ST1S40PUR operates at a fixed switching frequency of 1.5MHz. This high frequency allows the use of small external inductors and capacitors, reducing the overall solution footprint.

Is ST1S40PUR suitable for battery-powered applications?

Yes, the ST1S40PUR is suitable for battery-powered applications due to its low quiescent current of 1.5mA and shutdown current of less than 1uA. However, for very low standby power, consider a device with a lower quiescent current.

What is the efficiency of ST1S40PUR?

The ST1S40PUR achieves up to 90% efficiency in typical applications. Efficiency depends on input/output voltage ratio, load current, and external component selection.

Does ST1S40PUR have overcurrent protection?

Yes, the ST1S40PUR includes overcurrent protection (OCP) to safeguard the device and the load from excessive current. It also features thermal shutdown and under-voltage lockout (UVLO).

What is the package of ST1S40PUR?

The ST1S40PUR is available in a 6-pin DFN package (DFN6) measuring 3mm x 3mm. This compact package is suitable for space-constrained applications.

Can ST1S40PUR be used in automotive applications?

The ST1S40PUR is not AEC-Q100 qualified, so it is not recommended for automotive applications. For automotive-grade alternatives, consider devices with AEC-Q100 qualification.

What is the output voltage range of ST1S40PUR?

The output voltage of ST1S40PUR is adjustable from 0.8V to VIN, set by an external resistor divider. This flexibility allows it to generate common rails like 1.8V, 3.3V, and 5V.

Where can I buy ST1S40PUR online?

ST1S40PUR is available from major distributors such as DigiKey and Mouser. As of 2026-08-07, the price for 1 unit is approximately $1.25 USD. Check current stock and pricing on their websites.

What is the lead time for ST1S40PUR?

Lead time for ST1S40PUR varies by distributor and quantity. Typically, it ranges from 2 to 6 weeks for standard orders. Contact your preferred distributor for current lead times.

ST1S40PUR vs TPS54331 - which is better for a 12V to 3.3V conversion?

For a 12V to 3.3V conversion at up to 3A, both ST1S40PUR and TPS54331 are suitable. ST1S40PUR operates at 1.5MHz, allowing smaller components, while TPS54331 operates at 570kHz, potentially offering better efficiency at light loads. Choose ST1S40PUR for smaller size, TPS54331 for lower cost.

What is the difference between ST1S40PUR and ST1S40PHR?

ST1S40PUR and ST1S40PHR are the same device but in different packages. ST1S40PUR is in a DFN6 package, while ST1S40PHR is in a PowerSO-8 package. They are pin-compatible? No, they have different pinouts and are not drop-in replacements.

When should I choose ST1S40PUR over TPS54331?

Choose ST1S40PUR when you need a smaller solution size due to its 1.5MHz switching frequency, which allows smaller inductors and capacitors. Choose TPS54331 if you prefer a lower-cost solution and can tolerate larger external components.

What is the best drop-in replacement for ST1S40PUR?

The best drop-in replacement for ST1S40PUR is the ST1S40PHR (same die, different package - not drop-in). For a true drop-in, consider the TPS54331 (same DFN6 package? No, TPS54331 is SOIC-8). Verify pin compatibility before use.

Can TPS54331 replace ST1S40PUR?

TPS54331 is not a direct drop-in replacement for ST1S40PUR because it comes in a different package (SOIC-8 vs DFN6) and has a different pinout. PCB rework would be required. For a drop-in, look for devices in the same DFN6 package with compatible pinout.

Where can I download the ST1S40PUR datasheet PDF?

The ST1S40PUR datasheet is available for download from the STMicroelectronics website at https://www.st.com/resource/en/datasheet/st1s40.pdf. It contains full specifications, pinout, and application circuits.

Where can I find the ST1S40PUR pinout?

The ST1S40PUR pinout is detailed in the datasheet. The DFN6 package has pins for VIN, SW, GND, FB, EN, and a thermal pad. Refer to the datasheet for the exact pin assignments.

What are the key specifications of ST1S40PUR that engineers should know?

Key specifications of ST1S40PUR include: 4V to 18V input range, 3A output current, 1.5MHz switching frequency, adjustable output from 0.8V to VIN, 90% efficiency, 1.5mA quiescent current, and DFN6 package. These parameters define its suitability for high-current POL applications.

Hey Google, what can replace ST1S40PUR?

For a drop-in replacement of ST1S40PUR, you need a device in the same DFN6 package with pin compatibility. The ST1S40PHR is the same die but in a different package, so it is not drop-in. Cross-brand options like the TPS54331 are not pin-compatible. Always verify pinout before replacement.

Is ST1S40PUR the same as ST1S40PHR?

No, ST1S40PUR and ST1S40PHR are not the same. They share the same electrical specifications but differ in package: ST1S40PUR is DFN6, while ST1S40PHR is PowerSO-8. They are not pin-compatible and cannot be used interchangeably without PCB modification.

What is the best STMicroelectronics equivalent for ST1S40PUR?

The best STMicroelectronics equivalent for ST1S40PUR is the ST1S40PHR, which has identical electrical specifications but comes in a PowerSO-8 package. It is not a drop-in replacement due to different package and pinout.

Engineering reference data for ST1S40PUR — comparison, design guidance, and compliance information.

Selection Guide

Choose the ST1S40PUR when you need a compact, high-frequency (1.5MHz) buck converter for space-constrained applications like set-top boxes, networking gear, and LCD TVs. Its 3A output current and wide input range (4V to 18V) make it versatile for many POL designs. If you require a lower quiescent current for battery-powered devices, consider the TPS54331 (150uA vs 1.5mA). If you need a higher input voltage range (up to 28V), the TPS54331 is a better choice. For a pin-compatible drop-in, no direct alternative exists; the ST1S40PHR is the same die but in a different package, requiring PCB modification. For cost-sensitive designs, the MP2307 offers a lower switching frequency (340kHz) but may require larger external components.

Comparison with Alternatives

Parameter	This Product	ST1S40PHR	TPS54331	MP2307
Package	DFN6 (3x3 mm)	PowerSO-8	SOIC-8	SOIC-8
Brand	STMicroelectronics	STMicroelectronics	Texas Instruments	Monolithic Power Systems
Input Voltage Range	4V to 18V	4V to 18V	3.5V to 28V	4.75V to 23V
Output Current	3A	3A	3A	3A
Switching Frequency	1.5MHz	1.5MHz	570kHz	340kHz
Output Voltage Range	0.8V to VIN	0.8V to VIN	0.8V to VIN	0.8V to VIN
Quiescent Current	1.5mA	1.5mA	150uA	1mA
Enable Pin	Yes	Yes	Yes	Yes

Key Differentiators

Higher switching frequency (1.5MHz) enables smaller external components (vs TPS54331)
Same die as ST1S40PHR but in a smaller DFN6 package (vs ST1S40PHR)
Wide input voltage range (4V to 18V) with 3A output (vs MP2307)

Design Notes

For optimal performance, place the input capacitor (10uF ceramic) as close as possible to the VIN pin and the output inductor (2.2uH to 4.7uH) close to the SW pin. Use a solid ground plane and short, wide traces for high-current paths. The exposed pad should be soldered to a large copper area for thermal dissipation.

The DFN6 package has a thermal resistance of 45°C/W. At 3A output with a 12V to 3.3V conversion, power dissipation is approximately 2.6W, resulting in a temperature rise of 117°C. Ensure adequate copper area and airflow to keep the junction temperature below 150°C.

Do not exceed the absolute maximum input voltage of 18V. Use a Schottky diode for the bootstrap capacitor if needed. Ensure the feedback resistor divider uses 1% tolerance resistors to maintain output voltage accuracy. The soft-start capacitor (if used) controls startup time; do not omit it if inrush current is a concern.