STMicroelectronics ST1S31PUR

Overview

ST1S31PUR from STMicroelectronics is a 3 A synchronous step-down DC-DC regulator with 2.8 V–5.5 V input, adjustable 0.8 V–VIN output, 1.5 MHz fixed-frequency PWM control, integrated 60 mΩ high-side and 45 mΩ low-side MOSFETs, and Power Good (PG) monitoring - deployed in FPGA core supplies and point-of-load power for consumer electronics.

For engineers reviewing the ST1S31PUR datasheet, ST1S31PUR pinout, ST1S31PUR application, or ST1S31PUR equivalent, this device delivers high-efficiency, compact DC/DC conversion for low-voltage, high-current embedded systems where thermal performance, cycle-by-cycle current limiting, and all-ceramic capacitor compatibility are critical selection criteria.

Technical Context

The ST1S31PUR implements peak current mode control with internal slope compensation to prevent sub-harmonic oscillation at duty cycles >50%. Its transconductance error amplifier (94 dB DC gain, 238 µA/V gm) features fully embedded RC/CC compensation (80 kΩ/55 pF), eliminating external components while ensuring 63° phase margin across load and input conditions.

Functional blocks include VIN-compatible enable logic (1.5 V ON / 0.5 V OFF thresholds), soft-start (400 µs ramp), hysteretic thermal shutdown (150 °C trip, 130 °C recovery), and dual-stage overcurrent protection: cycle-by-cycle current limit (4.0 A typ.) followed by current foldback (2.3 A) with adaptive frequency reduction during short-circuit events.

Key Specifications

Pinout & Package

ST1S31PUR is housed in a VFDFPN 3 mm × 3 mm, 8-lead package with exposed thermal pad (ePAD). The ePAD must be soldered to PCB ground plane for optimal thermal dissipation (R_thJA = 50 °C/W on demo board).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous step-down regulator applications.

Compared with TPS54331DR and MP2315GJ-Z, the ST1S31PUR offers tighter input voltage matching for 3.3 V/5 V systems, built-in PG signaling for reliable power sequencing, and internal soft-start - making it optimal for consumer electronics with strict size, thermal, and startup timing constraints.

Availability

ST1S31PUR is available at Aetrix Electronics and suitable for FPGA core supplies, set-top box point-of-load conversion, optical storage bias rails, and audio DSP power delivery requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for ST1S31PUR 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

STMicroelectronics is a global semiconductor leader headquartered in Geneva, specializing in power management, microcontrollers, and analog ICs for automotive, industrial, and consumer markets.

The ST1S31PUR belongs to ST's ST1Sxx series of monolithic synchronous buck regulators - designed specifically for high-efficiency, low-voltage, high-current point-of-load applications in space-constrained consumer electronics.

FAQ

What is the minimum recommended output capacitance for stable operation?

The ST1S31PUR supports all-ceramic output capacitors; ST recommends ≥47 µF MLCC (X5R/X7R) with ≤5 mΩ ESR for 1.2 V/3 A operation. Lower values (e.g., 22 µF) may be used with careful loop compensation verification, but 47 µF ensures adequate ripple suppression (<10 mV_pp) and phase margin >60° across temperature and load.

Can the ST1S31PUR operate with an input voltage below 2.8 V?

No - the absolute minimum operating input voltage is 2.8 V per datasheet Table 4. Below this, UVLO disables the regulator. The turn-on threshold is 2.4 V (typ.), but sustained operation requires ≥2.8 V to guarantee 3 A output current, proper current limiting, and thermal stability. Operation at 2.5 V is not characterized or guaranteed.

How is the Power Good (PG) pin used in system-level power sequencing?

The PG pin is an open-drain output that pulls low when V_OUT falls below 92% of its regulated value. It releases after a 170 µs delay once V_OUT recovers. In sequencing, PG from ST1S31PUR typically enables the next rail's EN pin or asserts a system POWER_GOOD signal - ensuring downstream logic only activates after stable core voltage is established.

Does the ST1S31PUR require an external compensation network?

No - the ST1S31PUR embeds full Type II compensation (80 kΩ RC, 55 pF CC) optimized for standard 1.0 µH inductors and 47 µF ceramic output capacitors. No external compensation components are needed; the internal network ensures stable operation across –40°C to +125°C junction temperature with >60° phase margin under all specified loads.