STMicroelectronics ST1S31D-R

Overview

ST1S31D-R from STMicroelectronics is a 3 A synchronous step-down DC-DC regulator with 2.8 V–5.5 V input range, adjustable 0.8 V–V_IN 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 ST1S31D-R datasheet, ST1S31D-R pinout, ST1S31D-R application, or ST1S31D-R equivalent, key selection criteria include verified 3 A continuous output capability, internal soft-start timing (400 µs), cycle-by-cycle current limiting with foldback protection, all-ceramic capacitor compatibility, and VFDFPN 3×3–8L thermal performance (R_thJA = 50 °C/W).

Technical Context

The ST1S31D-R implements peak current mode control with fully integrated oscillator, slope compensation, and internal transconductance error amplifier (94 dB DC gain, 238 µA/V g_m). Its fixed 1.5 MHz switching frequency enables compact filter design while maintaining stability across load and line variations.

It features embedded compensation (R_C = 80 kΩ, C_C = 55 pF), hysteretic thermal shutdown (150 °C trip, 130 °C recovery), and dual overcurrent protection: cycle-by-cycle limiting at 4.0 A and current foldback activation when FB < 0.2 V - reducing switching frequency to sustain ~2.3 A short-circuit current.

Key Specifications

Pinout & Package

ST1S31D-R is housed in a VFDFPN 3 mm × 3 mm, 8-lead package with exposed thermal pad (ePAD) connected to PGND for enhanced thermal dissipation (R_thJA = 50 °C/W). The ePAD must be soldered to PCB ground plane for optimal thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS54331DR and MP2315DJ-LF-Z, ST1S31D-R uniquely supports 2.8 V input, integrates PG and foldback protection, and delivers 3 A in a thermally optimized 3×3 mm VFDFPN - making it the sole fit for compact, low-VIN, high-reliability point-of-load designs.

Availability

ST1S31D-R is available at Aetrix Electronics and suitable for FPGA core supplies, optical storage power rails, and audio DSP point-of-load applications requiring stable component supply, long-term lifecycle assurance, and traceable sourcing.

Supply support for ST1S31D-R 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, Switzerland, designing and manufacturing analog, MCU, power, and sensor solutions for automotive, industrial, and consumer markets.

ST1S31D-R belongs to ST's ST1S series of monolithic synchronous buck regulators - engineered specifically for high-efficiency, low-voltage, high-current point-of-load conversion in space-constrained consumer and computing applications.

FAQ

What is the minimum output voltage achievable with ST1S31D-R?

The ST1S31D-R regulates output down to 0.8 V, set by its internal reference voltage. This value is guaranteed across temperature (−40 °C to +125 °C) and load (10 mA to 3 A) with ±1% tolerance. Lower voltages are not supported - the feedback amplifier architecture requires ≥0.8 V at the FB pin for stable regulation.

Can ST1S31D-R operate with only ceramic capacitors on input and output?

Yes - the ST1S31D-R is explicitly designed for all-ceramic operation. Its peak current mode control and internal compensation ensure stability with low-ESR MLCCs. Recommended input: ≥10 µF X5R/X7R ceramic near VINSW; output: ≥47 µF MLCC with appropriate voltage rating and ripple current rating.

How does the Power Good (PG) pin behave during startup and fault conditions?

The PG pin remains low until V_OUT reaches 92% of its target (e.g., 0.736 V for 0.8 V setting), then releases after 170 µs delay. If V_OUT drops below that threshold - due to overload, short, or input dropout - PG pulls low immediately with no delay, providing fast fault signaling to host logic.

What thermal derating applies to ST1S31D-R in VFDFPN package at 60 °C ambient?

In VFDFPN 3×3–8L on a standard 4-layer PCB with 1 cm² exposed copper under ePAD, maximum continuous output current is 3 A up to 60 °C ambient. Above that, current must be reduced per R_thJA = 50 °C/W: at 85 °C ambient, max I_OUT ≈ 2.2 A to maintain T_J ≤ 150 °C.