STMicroelectronics STM805RM6F

Overview

STM805RM6F from STMicroelectronics is a 3 V microprocessor supervisory IC with battery switchover, active-high open-drain RST output, power-fail comparator (PFI/PFO), and manual reset input (MR). It guarantees reset assertion down to VCC = 1.0 V, features 200 ms typical reset timeout (trec), 1.6 s typical watchdog timeout, and draws only 40 µA typical supply current. It is used in industrial embedded systems to safeguard SRAM data during brownout events.

For engineers reviewing the STM805RM6F datasheet, STM805RM6F pinout, STM805RM6F application, or STM805RM6F equivalent, key selection criteria include its open-drain RST output configuration, VCC switchover threshold of 2.4 V, PFI comparator reference of 1.25 V, and compatibility with external low-power SRAM backup schemes.

Technical Context

The STM805RM6F integrates a precision voltage reference, dual comparators (reset and power-fail), a 1.6 s watchdog timer, and an automatic VCC/VBAT switchover circuit using an internal P-channel MOSFET switch. Its RST output is active-high and open-drain - distinct from push-pull variants in the same family - enabling wired-OR reset bus configurations.

It monitors VCC against a 2.63 V reset threshold (VRST) with 100 mV hysteresis, asserts PFO when PFI falls below 1.25 V or VCC drops below 2.4 V (VSW), and maintains VOUT continuity via VBAT during main supply loss. The MR input includes internal 40 kΩ pull-up and supports noise-immune push-button reset without external debounce.

Key Specifications

Pinout & Package

STM805RM6F is housed in an 8-pin SO8 (Small Outline Integrated Circuit) package, compliant with JEDEC MS-012, with 1.27 mm pitch and surface-mount footprint. Pin 1 is marked by a beveled corner or dot.

Key Features

Applications

Equivalent & Alternatives

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

Compared with STM805RM6F, STM805TSAF offers identical supervision functionality with packaging variation only, while MAX805LCSA+ trades watchdog and open-drain capability for lower 10 µA battery current - making it suitable only for static memory retention without runtime fault detection.

Availability

STM805RM6F is available at Aetrix Electronics and suitable for industrial data loggers, medical infusion pumps, smart energy meters, and PLC I/O modules requiring stable component supply across extended product lifecycles.

Supply support for STM805RM6F 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 silicon solutions for automotive, industrial, and embedded markets since 1987.

The STM690/805 supervisor family targets robust power-management in harsh environments, delivering guaranteed reset behavior, battery-backed SRAM protection, and integrated fault-detection features for mission-critical embedded systems.

FAQ

What is the function of the WDI pin on STM805RM6F?

The WDI (Watchdog Input) pin monitors microcontroller health by requiring a rising or falling edge at least once every 1.6 seconds. If no transition occurs, the internal watchdog timer expires and forces the open-drain RST output high. WDI cannot be left floating and must be actively toggled by firmware or driven by a dedicated oscillator circuit.

Can STM805RM6F drive SRAM directly without external FETs?

Yes - STM805RM6F delivers up to 75 mA through its VOUT pin when powered by VCC or VBAT, sufficient for most low-power SRAMs (e.g., Cypress CY14B101QN). For loads exceeding 75 mA, the Vccsw pin can drive an external PMOS transistor to augment current capacity while maintaining switchover control.

How does the PFI/PFO function interact with VCC monitoring?

PFI/PFO operates independently of the main reset comparator: PFO goes low when either PFI < 1.25 V OR VCC < 2.4 V (VSW), providing dual-path power-fail detection. This allows early warning from a separate auxiliary rail (e.g., analog sensor supply) while still responding to main supply collapse - critical for predictive shutdown sequencing.

Is the RST output truly open-drain, and what pull-up value is recommended?

Yes - STM805RM6F's RST is strictly open-drain active-high. ST recommends a 4.7 kΩ pull-up to 3 V for standard noise immunity and rise time (<100 ns). Values between 2.2 kΩ and 10 kΩ are acceptable depending on bus capacitance and speed requirements; avoid >10 kΩ to prevent slow edges in noisy environments.