STMicroelectronics SR2LARU

Overview

SR2LARU 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 6.0 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 5.0 V. It enables safe hard-reset initiation only after sustained button press, eliminating spurious resets in activity trackers and smartwatches.

For engineers reviewing the SR2LARU datasheet, SR2LARU pinout, SR2LARU application, or SR2LARU equivalent, this device supports dual-button reset arbitration, test-mode entry via overvoltage on SR0, glitch-immune timing, and flexible RST configuration (open-drain AL with no internal pull-up) - critical for space-constrained, battery-sensitive embedded designs.

Technical Context

The SR2LARU implements a dual-input synchronous reset architecture: both SR0 and SR1 must be held low simultaneously for ≥6.0 s (tSRC) to assert RST. Its logic ignores short presses (<6 s), preventing accidental system resets while allowing software interrupts via brief button closures. The absence of power-on reset (POR) requires external POR coordination or MCU-initiated boot validation.

Test mode is triggered by applying VCC + 0.9–1.4 V to SR0, initiating a 42 ms initial timer (tSRC-INI); subsequent SR0/SR1 ground pulses shorten tSRC to 21 ms for rapid functional verification. RST deasserts below 1.575 V (typ.), remaining valid down to 1.0 V - enabling robust operation across brown-out conditions.

Key Specifications

Pinout & Package

SR2LARU is housed in a 6-pin UDFN package (1.6 mm × 1.3 mm, 0.4 mm pitch), RoHS-compliant and halogen-free per ECOPACK®2. Pin 1 is marked by a dot; Pin 4 is NC (not bonded, must connect to VSS).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6369KA+T and TPS3808G18DBVR, SR2LARU uniquely delivers dual-button synchronized timing, factory-configured 6.0 s delay, and test-mode accessibility - making it the sole fit for wearable products requiring deliberate, glitch-immune, user-confirmed hard reset.

Availability

SR2LARU is available at Aetrix Electronics and suitable for activity tracker, smartwatch, and smartglasses applications requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for SR2LARU 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 microcontrollers, power management ICs, sensors, and analog chips for industrial, automotive, and consumer markets.

SR2LARU belongs to ST's Smart Reset™ supervisor product line, engineered specifically for ultra-low-power, space-constrained portable electronics where reliable, user-intent-driven system recovery is essential.

FAQ

What is the function of Pin 4 (NC) on SR2LARU?

Pin 4 is not internally bonded and has no electrical function. It must be connected to VSS (ground) for mechanical stability, thermal dissipation, and EMI suppression. Leaving it floating may cause solder joint reliability issues or unintended coupling in high-density layouts.

Does SR2LARU provide power-on reset (POR) functionality?

No. SR2LARU does not include a power-on reset circuit. It only responds to sustained assertion of SR0 and SR1 inputs. System POR must be handled externally - either by the host MCU's built-in POR, a separate POR IC, or a discrete RC network on the MCU's reset pin.

How is test mode entered and verified on SR2LARU?

Apply a voltage between VCC + 0.9 V and VCC + 1.4 V to SR0 while VCC is powered. The RST output will assert and remain low, providing visual feedback that test mode is active. To exit, cycle VCC (power-down then power-up); no software command is needed.

Can SR2LARU drive a reset pin directly on a 1.8 V MCU?

Yes - with an external pull-up resistor to 1.8 V. Since SR2LARU's RST is open-drain and specified down to 1.0 V VCC, it safely interfaces with 1.8 V I/O domains. Ensure the pull-up value (typically 10–47 kΩ) balances rise time and leakage; no level shifter is required.