STMicroelectronics SR2PARU

Overview

SR2PARU from STMicroelectronics is a 6-pin Smart Reset™ supervisor IC designed for ultra-low-power wearable systems. It features dual active-low push-button inputs (SR0/SR1), factory-programmed 7.5 s Smart Reset™ setup delay (tSRC), open-drain active-low reset output (RST), 1.65–5.5 V operating voltage, and 1.5 µA supply current at 5 V - enabling reliable hard-reset initiation only after sustained button press in smartwatches and activity trackers.

For engineers reviewing the SR2PARU datasheet, SR2PARU pinout, SR2PARU application, or SR2PARU equivalent, key selection criteria include tSRC timing precision across temperature, absence of power-on reset, configurable RST output type (open-drain vs. push-pull), and compatibility with microcontroller interrupt-driven reset arbitration in space-constrained, battery-powered edge devices.

Technical Context

The SR2PARU implements a dual-input, time-gated reset architecture where both SR0 and SR1 must be held low simultaneously for ≥7.5 s (typ.) before asserting RST - preventing accidental resets from brief button presses. Its logic ignores inputs below 1.575 V (typ.), ensuring clean deassertion during brownout, and guarantees valid RST levels down to 1.0 V.

It supports test mode entry via overvoltage on SR0 (VCC + 0.9 to +1.4 V), triggering a shortened 42 ms (typ.) tSRC-INI timer and feedback-indicated lock state. The device offers no fixed tREC pulse width (push-button controlled release), distinguishing it from tREC-equipped variants like SR2LABU.

Key Specifications

Pinout & Package

SR2PARU is housed in a 6-pin UDFN package (1.6 mm × 1.3 mm × 0.55 mm, 0.4 mm pitch) with exposed thermal pad (not bonded). Pin 1 is marked by dot; pin 4 is NC (not connected, internal die bond wire omitted).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar Smart Reset™ supervisor applications.

Compared with SR2LABU (fixed tREC) and SR2UARU (10 s tSRC), SR2PARU uniquely delivers push-button-controlled reset release with 7.5 s setup delay - optimizing for intuitive, user-directed recovery in compact battery-powered devices where precise timing and minimal BOM are critical.

Availability

SR2PARU is available at Aetrix Electronics and suitable for smartwatches, activity trackers, and smartglasses requiring stable component supply, ultra-low quiescent current, and factory-programmed Smart Reset™ timing.

Supply support for SR2PARU 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, delivering silicon solutions for automotive, industrial, and consumer markets since 1987.

SR2PARU belongs to ST's Smart Reset™ supervisor product line - engineered specifically for battery-constrained wearable electronics that demand intelligent, glitch-immune reset arbitration without firmware dependency.

FAQ

Does SR2PARU provide power-on reset (POR) functionality?

No. SR2PARU does not generate a power-on reset pulse. It only asserts RST in response to sustained dual-input activation (≥7.5 s). System POR must be handled externally - for example, by the MCU's internal POR circuit or a dedicated POR IC - as SR2PARU's reset behavior is purely event-triggered and voltage-monitored only for undervoltage release.

Can SR2PARU's tSRC delay be modified after manufacturing?

No. The 7.5 s tSRC delay in SR2PARU is factory-programmed and permanently fixed. It cannot be adjusted via external components, registers, or configuration pins. This ensures timing consistency and eliminates calibration overhead in production - users selecting variable tSRC must choose other variants like SR2HARU (4.0 s) or SR2UARU (10.0 s).

What is the purpose of the NC pin (Pin 4) and how should it be handled?

Pin 4 is internally not connected (NC) - no bond wire attaches to this pad. Per ST's layout guidance, it must be electrically tied to VSS (ground) on the PCB to prevent parasitic coupling and ensure signal integrity. Leaving it floating may induce noise on adjacent SR0/SR1 inputs or affect thermal performance due to uncontrolled heat dissipation paths.

How does SR2PARU behave during battery voltage drop below 1.575 V?

When VCC falls below 1.575 V (typ.), SR2PARU disables its Smart Reset™ logic and forces RST to deassert. The output remains in a known inactive state down to 1.0 V, ensuring clean release without glitches or metastability - critical for orderly MCU shutdown and data retention in fading battery conditions.