STMicroelectronics STM6821RWY6F

Overview

STM6821RWY6F from STMicroelectronics is a 5-pin precision voltage supervisor IC with integrated watchdog timer and manual reset input, designed for microprocessor reset management in embedded systems. It monitors 3.3 V power supplies, provides active-low push-pull RST output, asserts reset down to VCC = 1.0 V, features 1.4 ms reset pulse width (typ.), and consumes only 3 µA supply current (typ.) over –40 to +85 °C.

For engineers reviewing the STM6821RWY6F datasheet, STM6821RWY6F pinout, STM6821RWY6F application, or STM6821RWY6F equivalent, key selection criteria include guaranteed reset assertion at low VCC, watchdog timeout period of 1.6 s (typ.), compatibility with bidirectional MCU reset pins, and SOT23-5 footprint constraints.

Technical Context

The STM6821RWY6F implements a precision bandgap reference and comparator to monitor VCC against a fixed 3.3 V threshold (±2.5% accuracy). Its reset logic asserts RST low on VCC dropout, MR low, or WDI timeout - with trec = 1.4 ms ensuring reliable MCU initialization.

The watchdog timer clears on any WDI edge (≥50 ns pulse) and expires after 1.6 s of static WDI state; it is disabled when WDI is floating or tristated. The MR input includes an internal 52 kΩ pull-up, enabling direct switch-to-ground connection without external biasing.

Key Specifications

Pinout & Package

STM6821RWY6F is housed in a 5-pin SOT23-5 package (JEDEC MO-178AB), with 1.3 mm × 2.9 mm footprint, 0.95 mm height, and gull-wing leads for surface-mount assembly.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar voltage supervisor with watchdog applications.

Compared with STM6821RWY6F, STM6822RWY6F offers open-drain flexibility at the cost of added BOM component, while TPS3808G33DBVR omits watchdog supervision entirely - making STM6821RWY6F the sole option among these three that delivers both precise 3.3 V monitoring and integrated 1.6 s watchdog in SOT23-5.

Availability

STM6821RWY6F is available at Aetrix Electronics and suitable for industrial PLC controllers, portable medical sensors, automotive body control modules, and smart energy meters requiring stable component supply across extended product lifecycles.

Supply support for STM6821RWY6F 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, analog, and sensor solutions for industrial, automotive, and consumer markets.

STM6xxx is ST's dedicated family of 5-pin supervisors targeting cost-sensitive, space-constrained embedded systems needing reliable power-on reset, brown-out protection, and optional watchdog supervision - with STM6821RWY6F optimized for 3.3 V applications.

FAQ

What is the exact reset threshold voltage for STM6821RWY6F?

The STM6821RWY6F has a nominal VCC reset threshold of 3.3 V with ±2.5% tolerance over temperature (–40 to +85 °C), meaning the actual trip point falls between 3.2175 V and 3.3825 V. This value is trimmed during production and specified in Table 6 of the datasheet under "VTH Reset threshold voltage".

Can the watchdog timer be disabled on STM6821RWY6F?

Yes - the watchdog function is automatically disabled when the WDI pin is left unconnected (floating) or driven by a tristate buffer. In this state, the internal timer remains inactive, and reset assertion occurs only due to VCC dropout or MR activation. Leakage current must remain below 10 µA and load capacitance under 200 pF for reliable disable behavior.

Does STM6821RWY6F require an external pull-up resistor on the RST pin?

No - STM6821RWY6F features an active-low push-pull RST output, which actively drives both logic low and logic high states. Unlike open-drain variants (e.g., STM6822), it does not require an external pull-up resistor for proper MCU reset signaling, simplifying schematic design and reducing BOM count.

How does STM6821RWY6F behave during power-down sequences?

STM6821RWY6F guarantees valid RST assertion down to VCC = 1.0 V, meaning it continues to drive RST low as supply voltage collapses. Below 1.0 V, internal circuitry ceases operation but the last-driven state may persist briefly. For guaranteed reset validity to 0 V, ST recommends adding a 100 kΩ pull-down on RST - though this applies only to push-pull outputs and is not required for functional operation.