Nexperia USA Inc. STM6821TWY6F

Overview

STM6821TWY6F 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 (typ.), and guarantees reset assertion down to VCC = 1.0 V - enabling reliable boot sequencing in low-voltage brownout conditions.

For engineers reviewing the STM6821TWY6F datasheet, STM6821TWY6F pinout, STM6821TWY6F application, or STM6821TWY6F equivalent, this device supports critical reset integrity in MCU-based controllers where supply stability, watchdog supervision, and push-button recovery are required without external components.

Technical Context

The STM6821 implements a precision bandgap reference and comparator to monitor VCC against a fixed 3.3 V threshold (±2.5% over –40 to +85 °C), with reset deassertion delayed by a guaranteed 1.4 ms power-on reset timeout (trec). Its watchdog circuit triggers reset if WDI remains static for ≥1.6 s (typ.), and clears on any WDI edge (≥50 ns pulse width).

Reset output is active-low push-pull (RST), capable of sinking 20 mA while maintaining V_OL ≤ 0.4 V at I_SINK = 1.2 mA. The MR input includes an internal 52 kΩ pull-up, accepts TTL/CMOS logic levels, and holds reset asserted for trec after MR release - eliminating need for external debounce.

Key Specifications

Pinout & Package

STM6821TWY6F is housed in a standard SOT23-5 surface-mount package (3.0 × 1.7 × 1.3 mm), optimized for space-constrained PCB layouts and compatible with automated pick-and-place assembly.

Key Features

Applications

Use Value: Internal MR pull-up and 4.7 kΩ series resistor compatibility prevent signal contention with MCU reset pin, simplifying layout and validation.

Equivalent & Alternatives

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

Compared with MAX6326UT29D3+ and TPS3808G33DBVR, STM6821TWY6F uniquely combines 3.3 V supervision, integrated MR, 1.6 s watchdog, and sub-µA quiescent current in a single SOT23-5 package - making it optimal for cost-sensitive, space-constrained industrial controllers needing full reset autonomy.

Availability

STM6821TWY6F is available at Aetrix Electronics and suitable for industrial PLC controllers, smart energy meters, medical handheld diagnostics, and building automation nodes requiring stable component supply, long-lifecycle assurance, and RoHS-compliant sourcing.

Supply support for STM6821TWY6F 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 specializing in microcontrollers, power management, and analog/mixed-signal ICs, with strong focus on industrial, automotive, and IoT applications.

STM6xxx is ST's dedicated family of 5-pin supervisors targeting cost-effective, low-power microprocessor reset and watchdog functions in space-constrained industrial designs - emphasizing precision thresholding, guaranteed low-VCC operation, and minimal external component count.

FAQ

Can STM6821TWY6F monitor a 5 V supply?

No. STM6821TWY6F is factory-trimmed for 3.3 V ±2.5% threshold detection and is not specified for 5 V rail monitoring. For 5 V supervision, ST offers STM6822 (5 V variant) or STM6321 (5 V, open-drain RST). Using STM6821 on 5 V may result in premature or missed reset assertion due to threshold mismatch.

Is the watchdog function enabled by default?

Yes. The watchdog timer is active upon power-up and requires periodic WDI toggling to prevent timeout. It can be disabled by leaving WDI floating or connecting it to a tristate buffer output, provided leakage current stays below 10 µA and load capacitance remains under 200 pF per datasheet Section 2.4.

What is the maximum sink current capability of the RST output?

The RST output is rated for 20 mA maximum sink current with V_OL ≤ 0.4 V at I_SINK = 1.2 mA (Table 6, DC characteristics). This supports direct interface with most MCU reset pins and allows driving small external loads like LED indicators without additional buffering.

Does STM6821TWY6F support active-high reset output?

No. STM6821TWY6F provides only an active-low push-pull RST output. Devices with active-high RST (e.g., STM6823) or dual RST/RST outputs (e.g., STM6321) are separate part numbers in the STM6xxx family and are not pin-compatible replacements.