STMicroelectronics STM804RM6E

Overview

STM804RM6E from STMicroelectronics is a 3 V industrial-grade microprocessor supervisory IC with battery switchover, active-high open-drain RST output, power-fail comparator (PFI/PFO), manual reset (MR) input, and watchdog timer (WDI). It guarantees reset assertion down to VCC = 1.0 V, provides 200 ms typical reset timeout (trec), and draws only 40 µA typical supply current. It is used in embedded systems requiring non-volatile SRAM backup during main power loss, such as industrial controllers and metering devices.

For engineers reviewing the STM804RM6E datasheet, STM804RM6E pinout, STM804RM6E application, or STM804RM6E equivalent, key selection criteria include its open-drain active-high reset behavior, 2.4 V switchover threshold (VSW), 1.6 s watchdog timeout, PFI/PFO power-fail detection, and compatibility with external LPSRAM backup via VOUT/VBAT switching.

Technical Context

The STM804RM6E integrates a precision voltage reference, dual comparators (for VCC monitoring and PFI detection), a 1.6 s watchdog timer cleared by WDI edges, and an internal P-channel MOSFET switch enabling automatic VCC-to-VBAT switchover at 2.4 V with hysteresis. Its RST output is open-drain and active-high - asserted high during reset and released high-impedance otherwise - requiring an external pull-up for proper MCU interface.

It supports battery-backed SRAM supervision via VOUT, which connects to VCC when valid and switches to VBAT upon VCC drop below VSW; Vccsw provides a push-pull indicator signal of switchover state. The MR input features internal 40 kΩ pull-up and triggers reset on logic low, with trec timing applied post-release.

Key Specifications

Pinout & Package

STM804RM6E is housed in an 8-pin SO8 (Small Outline Integrated Circuit) package, measuring 4.9 mm × 3.9 mm × 1.75 mm, with 1.27 mm lead pitch and gull-wing leads. It is RoHS-compliant and rated for –40 °C to +85 °C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX6326UR26-T and TPS3808G12DBVR, STM804RM6E uniquely integrates battery switchover, PFI/PFO, and WDI in a single SO8 package - eliminating four external components and enabling compact, robust SRAM backup in space-constrained industrial designs.

Availability

STM804RM6E is available at Aetrix Electronics and suitable for industrial PLC controllers, smart electricity meters, medical infusion pumps, and building automation controllers requiring stable component supply, long-lifecycle support, and RoHS-compliant packaging.

Supply support for STM804RM6E 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 analog, MCU, power, and sensing solutions for industrial, automotive, and consumer markets.

The STM80x series is part of ST's precision power-supervision product line, engineered specifically for reliable, low-power microprocessor reset and battery-backed memory protection in harsh industrial environments.

FAQ

What is the function of the Vccsw pin on STM804RM6E?

Vccsw is a push-pull output that goes high when VOUT switches from VCC to VBAT, and low when VOUT reconnects to VCC. It provides a logic-level signal usable to drive the gate of an external PMOS transistor, enabling higher current (>75 mA) battery backup paths beyond the internal 100 Ω switch's capability.

Can STM804RM6E operate without a backup battery connected?

Yes - connect both VBAT and VOUT to VCC if no battery is used. In this configuration, VOUT remains tied to VCC, and all supervision functions (reset, watchdog, PFI/PFO) operate normally. The device draws only 40 µA typical supply current and guarantees RST assertion down to VCC = 1.0 V without battery assist.

How does the watchdog timer behave if the WDI pin is left unconnected?

If WDI floats or is held static (high or low), the watchdog timer times out every ~1.8 s (tWD + trec), asserting RST repeatedly. It cannot be disabled by leaving WDI unconnected - the timer requires regular edge transitions (rising or falling) to stay cleared, with minimum pulse width of 50 ns.

Is the PFO output compatible with 5 V logic systems?

Yes - PFO is a push-pull output with rail-to-rail swing (0 V to VCC), so when powered from a 3 V supply, it outputs 0 V / 3 V levels. To interface with 5 V logic, add a level-shifting buffer or use a pull-up to 5 V with current limiting, as PFO sinks up to 10 mA but does not source above VCC.