STMicroelectronics ST1S40IDR

Overview

ST1S40IDR from STMicroelectronics is a 3 A synchronous step-down DC-DC regulator with 4.0–18 V input range, adjustable 0.8 V output, 850 kHz fixed-frequency PWM control, integrated 95 mΩ high-side and 69 mΩ low-side MOSFETs, and internal soft-start - used for µP/ASIC/FPGA core and I/O power delivery in STB, TVs, and optical storage systems.

For engineers reviewing the ST1S40IDR datasheet, ST1S40IDR pinout, ST1S40IDR application, or ST1S40IDR equivalent, key selection criteria include peak current mode stability, ceramic-capacitor compatibility, cycle-by-cycle overcurrent protection, thermal shutdown hysteresis (150 °C trip / 130 °C recovery), and enable threshold (1.2 V ON / 0.4 V OFF).

Technical Context

The ST1S40IDR implements peak current mode control with an internally compensated transconductance error amplifier (Gm = 251 µA/V, DC gain = 95 dB) and slope compensation to prevent sub-harmonic oscillation above 50% duty cycle. Its oscillator delivers a stable 850 kHz switching frequency with ±15% tolerance across temperature and line.

Functional blocks include high-side current sensing, diode-emulation low-side sensing, UVLO monitoring on both VINA and VINSW, and dual-stage overcurrent protection: pulse-by-pulse limiting at 4.0–6.0 A (OCP1), followed by current fold-back to ~2 A and ¼-frequency reduction when FB < 0.3 V, plus hard shutdown at OCP2 (~1 A above OCP1) during severe short-circuit.

Key Specifications

Pinout & Package

ST1S40IDR is packaged in HSOP-8 (exposed pad), with pin 1 = VINA, pin 2 = EN, pin 3 = FB, pin 4 = AGND, pin 5 = NC (connect to GND), pin 6 = VINSW, pin 7 = SW, pin 8 = PGND. The exposed thermal pad (ePad) is mandatory and must be soldered to a dedicated GND copper area for thermal performance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS54302DDAR and MP2315DJ-LF-Z, ST1S40IDR offers superior integration (internal compensation, fold-back, hysteresis), tighter output accuracy (±2.5% vs ±3%), and optimized ceramic-capacitor compatibility - reducing design risk and validation effort for consumer electronics point-of-load use cases.

Availability

ST1S40IDR is available at Aetrix Electronics and suitable for set-top box power rails, TV mainboard core supplies, optical storage logic/motor drives, and FPGA configuration rails requiring stable component supply, long-term lifecycle assurance, and consistent parametric performance across production batches.

Supply support for ST1S40IDR 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, power, microcontroller, and sensor solutions for automotive, industrial, and consumer markets.

ST1S40IDR belongs to ST's ST1Sxx family of synchronous step-down regulators, engineered specifically for high-efficiency, low-component-count point-of-load conversion in space-constrained consumer electronics with strict thermal and EMI requirements.

FAQ

What is the minimum output voltage achievable with ST1S40IDR?

The ST1S40IDR regulates down to 0.8 V, set by its internal reference voltage. This value is fixed and not adjustable lower - any output below 0.8 V requires an external reference or post-regulation, as the feedback amplifier is designed around this precise threshold.

Can ST1S40IDR operate with 100% duty cycle?

Yes - the ST1S40IDR supports 100% duty cycle operation, enabling dropout regulation (V_OUT ≈ V_IN – I_OUT × R_{DS(on)_HS}) when input voltage approaches the desired output, such as generating 4.8 V from a 5 V source under light load.

Is an external bootstrap capacitor required for ST1S40IDR?

No - ST1S40IDR integrates all necessary gate drive circuitry and does not require an external bootstrap capacitor. Its internal architecture uses charge-pump-based high-side driver, eliminating the need for external floating bias components.

How does the NC pin (Pin 5) affect layout or functionality?

Pin 5 is labeled "NC" but is electrically connected to the die substrate and must be soldered to AGND or PGND plane for optimal thermal and EMI performance. Leaving it unconnected degrades thermal resistance and may cause instability due to floating substrate potential.