STMicroelectronics ISO808A

Overview

ISO808A from STMicroelectronics is a galvanically isolated octal high-side power solid-state relay with SPI interface, designed for driving inductive loads in industrial control systems. It features 8 independent high-side channels, VCC operating range of 9.2–36 V, R_DS(on) = 0.125 Ω (typ), per-channel over-temperature protection, and integrated VCC Power Good and common FAULT diagnostics - deployed in PLC I/O modules requiring robust load switching under EMI-heavy factory environments.

For engineers reviewing the ISO808A datasheet, ISO808A pinout, ISO808A application, or ISO808A equivalent, this device is selected for its dual-isolated supply architecture (VCC/VDD), daisy-chainable SPI interface up to 20 MHz, channel-level thermal independence, and compliance with IEC 61000-4-2/4/5/8, UL1577, and IEC 60747-17 safety standards.

Technical Context

The ISO808A implements two galvanically isolated voltage domains: Process Stage (VCC/GNDCC) for 8 high-side power outputs, and Control Logic Stage (VDD/GNDDD) for SPI communication and register management. Communication occurs via ST's proprietary isolation protocol, not standard digital isolators - enabling synchronized 8-bit output status transfer and fault reporting through SDO on CLK falling edges.

Each channel integrates independent junction over-temperature shutdown (TJSD = 150–200 °C) and restart (TJR = 160 °C), plus case-level over-temperature protection (TCSD = 125–135 °C). Short-circuit current limiting is set at 0.7 A (ISO808A) or 1 A (ISO808A-1), with fast demagnetization (V_DEMAG = VCC − 54 V typ) critical for solenoid and relay coil turn-off in motion control.

Key Specifications

Pinout & Package

ISO808A is packaged in PowerSO-36, a thermally enhanced surface-mount package with exposed VCC-connected tab (TAB(VCC)) and GNDCC-connected thermal pad (TAB(GNDCC)). The 36-pin layout separates logic (VDD, GNDDD, SPI) and power (VCC, GNDCC, OUT1–OUT8) domains physically and electrically to preserve creepage (2.6 mm) and clearance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar galvanically isolated high-side driver applications.

Compared with TPL7407LA and ADUM3050, the ISO808A uniquely integrates galvanic isolation, 8-channel high-side drive, SPI control, and comprehensive diagnostics into a single PowerSO-36 package - eliminating external isolation, protection, and level-shifting components required by alternatives.

Availability

ISO808A is available at Aetrix Electronics and suitable for programmable logic controllers, industrial PC peripheral I/O, numerical control machines, and high-inductive-load drivers requiring stable component supply across extended product lifecycles.

Supply support for ISO808A 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 automotive, industrial, and power management ICs with vertical manufacturing and broad safety-certified portfolio.

The ISO808A belongs to ST's industrial isolated drivers product line, engineered specifically for high-reliability programmable automation controllers where functional safety, surge immunity, and long-term supply stability are mandatory.

FAQ

What is the maximum continuous output current per channel for ISO808A?

The ISO808A supports continuous output current up to 0.7 A per channel, with internal short-circuit current limiting set at 0.7 A (min) and thermal shutdown triggered at junction temperatures exceeding 150–200 °C. This rating assumes proper PCB thermal design with GNDCC pad soldered to ≥4 cm² copper area to maintain R_{th j-amb} ≤ 16.9 °C/W.

Does ISO808A support daisy-chained SPI communication?

Yes - ISO808A supports daisy-chained SPI configurations using the SDO pin as serial output shift register. When SS remains low beyond 8 clock cycles, the internal Output Status Register shifts out to SDO, allowing multiple devices to share one SPI bus with minimal GPIO usage. Timing requires t_dis(SDO) ≤ 20 ns and t_a(SDO) ≤ 25 ns for reliable cascading.

How does the FAULT pin behave during a junction over-temperature event?

The FAULT pin goes active-low and remains latched until the fault condition clears and a new SPI command is issued. During junction over-temperature (TJ > TJSD), the affected channel turns OFF and FAULT asserts; it stays asserted even after TJ falls below TJR unless the microcontroller sends a fresh 8-bit output status frame - ensuring persistent fault visibility across power cycles or communication gaps.

Can ISO808A drive 24 V AC solenoids directly?

No - ISO808A is a DC high-side switch rated for VCC up to 36 V DC only. It cannot commutate AC waveforms or withstand reverse polarity during AC zero-crossing. For 24 V AC solenoids, use ISO808A with an external AC-to-DC rectifier and hold circuit, or select a dedicated AC solid-state relay like ST's VIPower M0-7 series with zero-crossing detection.