STMicroelectronics SCLT3-8BT8

Overview

SCLT3-8BT8 from STMicroelectronics is an octal industrial digital input IC with current-sinking inputs compliant to IEC 61131-2 Types 1, 2, and 3, featuring 2.35 mA typical input current limitation, 20 µs–3 ms configurable digital filtering, and SPI serial interface (8-/16-bit mode with parity and diagnostics). It integrates a 5 V regulator, energyless LED drivers, and operates from −40 °C to 105 °C in HTSSOP-38 package - deployed in PLC input modules for factory automation.

For engineers reviewing the SCLT3-8BT8 datasheet, SCLT3-8BT8 pinout, SCLT3-8BT8 application, or SCLT3-8BT8 equivalent, key selection criteria include IEC 61131-2 Type compliance, daisy-chain SPI capability, reverse polarity tolerance (±35 V), EMC robustness (IEC 61000-4-2 level 4), and thermal performance at 105 °C ambient.

Technical Context

The SCLT3-8BT8 implements a dual-stage digital glitch filter controlled by an external oscillator resistor (ROSC = 15 kΩ–1.5 MΩ), enabling programmable filtering times from 20 µs to 3 ms via 8× or 64× clock division selected by the DVR pin. Its input comparators feature 1.0 V hysteresis and thresholds of 4.3 V (L→H) and 3.3 V (H→L) with 2.35 mA current limiting across all eight channels.

It supports SPI communication with CPOL = 0, CPHA = 0 timing, delivering either 8-bit raw input data (SPM = VDD) or 16-bit frames including input states, UVA/OTA alarms, and 4 parity bits (SPM = GND). The /MISO output provides inverted data for noise-immune isolation schemes, while the integrated 5 V regulator powers downstream logic.

Key Specifications

Pinout & Package

Package: HTSSOP-38, 0.5 mm pitch, 9.7 mm × 4.4 mm footprint, exposed thermal pad (TAB) connected to COMP.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar octal industrial digital input applications.

Compared with TIDA-01603 and AD7403, the SCLT3-8BT8 delivers turnkey IEC 61131-2 compliance, integrated power management, and serialized diagnostics - reducing design cycle time by 6+ weeks and eliminating 12+ passive components per channel versus discrete alternatives.

Availability

SCLT3-8BT8 is available at Aetrix Electronics and suitable for programmable logic controller input modules, CNC machine tool interfaces, and motor control safety I/O expansion requiring stable component supply, long-term industrial lifecycle support, and guaranteed traceable sourcing.

Supply support for SCLT3-8BT8 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 industrial, automotive, and power management solutions, with over 40 years of expertise in ruggedized analog and mixed-signal ICs.

The SCLT3 series targets high-density industrial I/O modules, designed to replace optocoupler-based input stages by integrating current limiting, filtering, serialization, and diagnostics into a single package - reducing thermal load and board space in PLC and motion control systems.

FAQ

What is the maximum field input frequency supported in 8-bit SPI mode?

The SCLT3-8BT8 supports up to 20 kHz input frequency in 8-bit mode, verified under conditions of VI = 24 V, RI = 2.2 kΩ, and tFT ≥ 50 µs. This is enabled by its internal comparator bandwidth and 2.35 mA current limit, which ensure clean edge detection without aliasing or metastability in fast-switching factory sensors.

How does the SCLT3-8BT8 handle loss of 24 V bus power?

When VC drops below 9 V, the internal POR circuit forces MISO low and disables SPI output; the final stop bit in the 16-bit frame goes low, providing a hardware-detectable power-loss flag. This allows host controllers to initiate safe shutdown sequences before complete system collapse.

Can the SCLT3-8BT8 be used for IEC 61131-2 Type 2 inputs?

Yes - Type 2 compliance (6 mA min input current) is achieved by paralleling two INx channels with RREF = 9.1 kΩ and RI = 0.75 kΩ, yielding ~7 mA total current. This configuration is validated in AN2846 and maintains full EMC performance without external active components.

What is the thermal resistance (R_th(j-a)) of the HTSSOP-38 package at 105 °C ambient?

With 70 mm² of 35 µm copper on FR4, the SCLT3-8BT8 achieves R_th(j-a) ≈ 70 °C/W, enabling full 105 °C operation at 12 mA IDD and 8 × 2.35 mA input current. Exposed TAB must be soldered to COMP plane for thermal performance; thermal pad area ≥ 25 mm² recommended.