STMicroelectronics STM6821SWY6F

Overview

STM6821SWY6F from STMicroelectronics is a 5-pin precision voltage supervisor IC with integrated watchdog timer and manual reset input, designed for microprocessor power monitoring in industrial embedded systems. It monitors VCC at 3.3 V (±2.5%), asserts active-low push-pull RST for ≥1.4 ms, features 1.6 s watchdog timeout, and guarantees reset assertion down to VCC = 1.0 V - used in PLC controllers and motor drive firmware recovery circuits.

For engineers reviewing the STM6821SWY6F datasheet, STM6821SWY6F pinout, STM6821SWY6F application, or STM6821SWY6F equivalent, key selection criteria include reset threshold accuracy, watchdog timeout stability over temperature, MR input internal pull-up value (52 kΩ), and guaranteed RST validity below 1.0 V VCC during brownout conditions.

Technical Context

The STM6821 implements a precision bandgap reference and comparator-based VCC monitoring circuit that triggers reset when supply drops below 3.3 V ±2.5%. Its watchdog timer resets on WDI inactivity exceeding 1.6 s (typ.), cleared by any edge transition - supporting fail-safe MCU supervision without external timing components.

It provides dual reset outputs: active-low push-pull RST (Pin 3) and active-high push-pull RST (Pin 5), both asserted synchronously during VCC fault, MR low, or watchdog timeout. The MR input includes an internal 52 kΩ pull-up, enabling direct switch-to-ground connection without external biasing.

Key Specifications

Pinout & Package

STM6821SWY6F is housed in a standard SOT23-5 surface-mount package (2.9 mm × 1.6 mm × 1.1 mm), optimized for space-constrained PCB layouts in industrial control modules and sensor nodes.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar voltage supervision and watchdog applications.

Compared with MAX6326UT33+T and TPS3808G33DBVR, STM6821SWY6F uniquely delivers simultaneous active-low and active-high push-pull reset outputs in SOT23-5, enabling direct interface to diverse MCU reset architectures without added components or timing compromises.

Availability

STM6821SWY6F is available at Aetrix Electronics and suitable for industrial PLC controllers, motor drive firmware recovery systems, smart sensor nodes, and energy-efficient gateways requiring stable component supply across extended product lifecycles.

Supply support for STM6821SWY6F 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, specializing in microcontrollers, power management, and analog/mixed-signal ICs for industrial, automotive, and consumer markets.

The STM6xxx series was developed specifically for robust, low-power microprocessor supervision in harsh industrial environments - emphasizing guaranteed reset behavior under brownout, integrated watchdog reliability, and minimal external component count.

FAQ

Can STM6821SWY6F monitor voltages other than 3.3 V?

No - STM6821SWY6F is factory-trimmed for a precise 3.3 V ±2.5% reset threshold. It does not support adjustable or multiple voltage thresholds. For 5 V, 2.5 V, or 3.0 V monitoring, ST offers pin-compatible variants including STM6822 (5 V), STM6823 (3.0 V), and STM6824 (2.5 V), all in SOT23-5.

How is the watchdog timer disabled on STM6821SWY6F?

The watchdog is disabled by leaving the WDI pin unconnected (floating) or connecting it to a tristate buffer output. When floating, internal leakage keeps WDI within valid logic levels, and the watchdog counter is automatically serviced. Maximum allowable leakage is 10 µA and load capacitance is 200 pF per datasheet Section 2.4.

What is the maximum sink/source current capability of the RST outputs?

Both RST (Pin 3) and RST (Pin 5) are push-pull outputs rated for ±20 mA DC output current per Absolute Maximum Ratings (Table 4). Typical V_OL is <0.4 V at 1.2 mA sink, and V_OH is >VCC–0.4 V at 1.2 mA source - sufficient to directly drive standard CMOS/TTL reset inputs without buffering.

Does STM6821SWY6F require external capacitors for stable operation?

No external capacitors are required for basic supervision or watchdog operation. The device is fully self-contained. A 0.1 µF bypass capacitor on VCC is recommended per standard analog IC practice, but no timing, filtering, or debouncing capacitors are needed - the MR input is internally debounced and the watchdog uses an on-chip oscillator.