STMicroelectronics AST1S31PUR

Overview

AST1S31PUR from STMicroelectronics is an automotive-grade synchronous step-down switching regulator designed to generate low-voltage rails from a 2.8 V to 4 V input supply. The device provides up to 3 A DC output current, uses fixed-frequency PWM operation at 1.5 MHz, and integrates both the high-side power switch and synchronous rectifier to reduce external component count.

For engineers reviewing the AST1S31PUR datasheet, AST1S31PUR pinout, AST1S31PUR application, or AST1S31PUR equivalent, this regulator is most relevant for automotive point-of-load power rails, battery-powered modules, car body electronics, MCU core supplies, ASIC / DSP / FPGA I/O rails, and compact systems requiring adjustable output voltage from 0.8 V, AEC-Q100 qualification, Power Good monitoring, internal soft-start, and VFDFPN 3 x 3 mm assembly.

Technical Context

AST1S31PUR uses peak current mode control to regulate the output voltage through the FB pin. The internal 0.8 V reference is compared with the feedback voltage, while the current-sense signal controls the switching duty cycle. This control structure helps the regulator respond to load changes while keeping the external compensation network unnecessary in many compact automotive point-of-load designs.

The device integrates a 70 mΩ high-side switch and a 55 mΩ synchronous rectifier, so the main conduction path is inside the IC rather than built from an external diode and MOSFET pair. Its 1.5 MHz switching frequency allows smaller inductors and ceramic capacitors, while Power Good, enable control, soft-start, cycle-by-cycle current limiting, foldback short-circuit protection, and thermal shutdown support robust low-voltage rail generation in automotive modules.

Key Specifications

Pinout & Package

AST1S31PUR is supplied in a VFDFPN 3 x 3 mm 8-lead package with an exposed pad connected to ground. The pinout separates analog input, switching input, analog ground, power ground, feedback, enable, Power Good, and the SW switching node, which helps the layout keep noisy switching current paths away from the feedback and control reference.

Key Features

• Automotive-grade synchronous step-down regulator with AEC-Q100 qualification.
• 3 A DC output current for compact low-voltage power rails.
• 2.8 V to 4 V input voltage range for regulated low-voltage input systems.
• Adjustable output voltage from 0.8 V up to VIN.
• 1.5 MHz fixed-frequency PWM operation for small inductor and capacitor selection.
• Integrated 70 mΩ high-side switch and 55 mΩ synchronous rectifier.
• Peak current mode control with internal compensation.
• Internal soft-start and enable control.
• Open-drain Power Good output for rail monitoring and sequencing.
• Cycle-by-cycle current limiting and current foldback short-circuit protection.
• VFDFPN 3 x 3 mm 8-lead package with exposed pad.

Applications

Equivalent & Alternatives

When evaluating AST1S31PUR equivalent devices, engineers should compare automotive qualification, input voltage range, output current, switching frequency, package footprint, feedback reference, Power Good behavior, protection features, thermal layout, and whether the existing PCB uses the VFDFPN 3 x 3 mm pin arrangement.

AST1S31PUR replacement decisions should treat package layout, qualification level, switching frequency, thermal behavior, and feedback network requirements as linked design items. A regulator with the same output current rating may still require inductor, capacitor, EMI, and validation changes before use in a production power rail.

Quality

AST1S31PUR should be sourced as original STMicroelectronics automotive-grade components through traceable and controlled supply channels. Quality verification procedures may include VFDFPN package inspection, top-mark review, tape-and-reel label inspection, moisture sensitivity handling review, exposed-pad condition check, solderability testing, X-ray inspection for bottom-pad solder coverage, input-current screening, output regulation testing, Power Good functional testing, and incoming inspection suited to automotive power-management IC production requirements.

Availability

AST1S31PUR is available at Aetrix Electronics and suitable for automotive point-of-load regulators, battery-powered modules, car body electronics, MCU power rails, ASIC / DSP / FPGA core supplies, low-voltage control boards, and compact systems requiring stable component supply and repeatable production support.

Supply support may include scheduled delivery planning, volume procurement support, BOM continuity assistance, traceable sourcing management, and lifecycle availability coordination for automotive electronics manufacturers, industrial control suppliers, contract manufacturers, repair groups, and low-voltage power-module builders.

For production deployment, confirming the VFDFPN 3 x 3 mm footprint, exposed-pad layout, 2.8 V to 4 V input requirement, output-current margin, inductor saturation rating, ceramic capacitor selection, feedback-divider values, Power Good usage, EN logic level, thermal dissipation, and automotive qualification requirement helps reduce sourcing and manufacturing risk.

Manufacturer

STMicroelectronics supplies power-management ICs, microcontrollers, automotive ICs, analog devices, sensors, protection components, memories, RF products, and discrete semiconductors for industrial, automotive, consumer, communication, and embedded applications. AST1S31PUR belongs to ST's automotive buck regulator portfolio for compact synchronous step-down conversion in low-voltage vehicle electronic systems.

FAQ

What is AST1S31PUR used for?

AST1S31PUR is used as an automotive synchronous step-down regulator for low-voltage point-of-load rails. It converts a 2.8 V to 4 V input into an adjustable output as low as 0.8 V, supporting MCU, ASIC, DSP, FPGA, body electronics, and battery-powered module supplies.

What input voltage range does AST1S31PUR support?

AST1S31PUR supports a 2.8 V to 4 V operating input voltage range. This makes AST1S31PUR suitable for regulated low-voltage intermediate rails, not direct 12 V automotive battery conversion. Designs should confirm that the available input rail stays inside this range during startup, load steps, and fault conditions.

What is the output current rating of AST1S31PUR?

AST1S31PUR provides up to 3 A DC output current. The actual usable current in a product depends on input voltage, output voltage, switching losses, inductor selection, PCB copper area, exposed-pad soldering, airflow, and junction temperature margin in the final operating environment.

What package does AST1S31PUR use?

AST1S31PUR uses a VFDFPN 3 x 3 mm 8-lead package with an exposed pad connected to ground. The small package supports compact automotive layouts, but it also requires careful thermal copper design, short switching-current loops, and clean separation between feedback routing and the SW node.

How is the output voltage set on AST1S31PUR?

AST1S31PUR uses the FB pin and an internal 0.8 V reference for output regulation. Connecting the output directly to FB sets a 0.8 V output, while higher output voltages use an external resistor divider from VOUT to FB and ground to define the regulated voltage.

What are common AST1S31PUR alternatives?

Common AST1S31PUR comparison options include AST1S31HF and ST1S31PUR. AST1S31HF keeps the automotive 2.8 V to 4 V concept but uses 2.3 MHz switching, while ST1S31PUR provides a related 3 A, 1.5 MHz regulator option with a wider 2.8 V to 5.5 V input range for standard designs.