STMicroelectronics STM804SM6E

Overview

STM804SM6E 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, provides 200 ms typical reset timeout (trec), 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 STM804SM6E datasheet, STM804SM6E pinout, STM804SM6E application, or STM804SM6E equivalent, key selection criteria include its open-drain active-high reset output, automatic VCC-to-VBAT switchover at 2.4 V, PFI threshold of 1.25 V, and compatibility with external LPSRAM backup circuits.

Technical Context

The STM804SM6E integrates a precision voltage reference, dual comparators (for VCC monitoring and PFI detection), and a trec timer circuit that ensures minimum 200 ms reset pulse width after power-up or MR release. Its internal logic asserts RST high when VCC exceeds VRST (2.63 V) and remains high for trec, then releases it - but only if no watchdog timeout or MR assertion occurs.

VOUT is driven by an internal P-channel MOSFET switch with 100 Ω on-resistance, enabling seamless transition from VCC to VBAT (≥1 V) when VCC falls below VSW = 2.4 V. The PFO output is push-pull and asserts low when either VCC < 2.4 V or PFI < 1.25 V, providing early power-fail warning to the host system.

Key Specifications

Pinout & Package

STM804SM6E is housed in an 8-pin SO8 (Small Outline Integrated Circuit) package, measuring 4.9 mm × 6.0 mm × 1.75 mm, with 1.27 mm lead pitch and gull-wing leads. It is RoHS-compliant and lead-free.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX809SEUR+T and TPS3808G33DBVR, STM804SM6E uniquely integrates VCC/VBAT switchover, open-drain RST, and PFI/PFO in one SO8 package - eliminating four external components and enabling single-chip SRAM data retention in space-constrained industrial designs.

Availability

STM804SM6E is available at Aetrix Electronics and suitable for industrial PLC controllers, medical infusion pumps, smart energy meters, and ruggedized telematics units requiring stable component supply across multi-year production cycles.

Supply support for STM804SM6E 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 microcontrollers, power management ICs, sensors, and analog devices for industrial, automotive, and consumer markets.

STM804SM6E belongs to ST's legacy supervisor family targeting cost-sensitive, high-reliability embedded systems. It was engineered specifically to simplify non-volatile SRAM backup architecture while maintaining industrial temperature and long-term supply stability.

FAQ

What is the function of the Vccsw pin on STM804SM6E?

Vccsw is a push-pull output that goes high when VOUT switches from VCC to VBAT, and low when VOUT reconnects to VCC. It is designed 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. It does not control internal switchover - that is fully autonomous.

Can STM804SM6E be used without a backup battery?

Yes. When no battery is used, connect both VBAT and VOUT pins directly to VCC. This disables switchover functionality while preserving reset supervision, PFI/PFO monitoring, and MR input operation. The device draws only 40 µA and asserts RST correctly down to VCC = 1.0 V, making it fully functional as a standalone reset supervisor.

How does the PFI input interact with the power-fail detection?

PFI is a dedicated analog input referenced to VSS with a fixed 1.25 V threshold. When PFI voltage falls below 1.25 V - regardless of VCC level - PFO asserts low. This allows independent monitoring of a secondary rail (e.g., analog sensor supply) while VCC remains nominal, enabling selective subsystem shutdown before main power failure.

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

Yes, RST is a true open-drain output per datasheet Figure 1 and Table 2. It requires an external pull-up resistor to VCC or another logic rail (e.g., 3.3 V or 5 V). A 10 kΩ resistor is typical; lower values improve rise time for fast-reset applications, while higher values reduce standby current. No internal pull-up exists on this pin.