The XC3S50-4PQ208I is a field-programmable gate array (FPGA) from Xilinx’s Spartan-3 family, designed for high-volume, cost-sensitive applications that demand reliable programmable logic. Manufactured under the AMD Xilinx brand, this device delivers 50,000 system gates in a compact 208-pin PQFP package — making it a go-to solution for engineers working in industrial, telecommunications, automotive, and consumer electronics design.

If you are looking for a proven, low-cost Xilinx FPGA for your next embedded design, the XC3S50-4PQ208I offers an excellent balance of performance, I/O flexibility, and on-chip resources.

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What Is the XC3S50-4PQ208I?

The XC3S50-4PQ208I belongs to the eight-member Spartan-3 FPGA family, which ranges from 50,000 to 5,000,000 system gates. This specific part number breaks down as follows:

The “I” suffix is significant: it confirms the device is rated for industrial operating temperatures, making it suitable for designs deployed in harsh or outdoor environments.

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XC3S50-4PQ208I Key Specifications

Core Logic Resources

Memory & I/O

Electrical & Package Characteristics

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XC3S50-4PQ208I Architecture Overview

Configurable Logic Blocks (CLBs)

The Spartan-3 CLB architecture consists of four slices, each containing two 4-input look-up tables (LUTs) and two flip-flops. The 192 CLBs in the XC3S50-4PQ208I can be used for combinational logic, synchronous registers, or distributed RAM — giving designers flexibility in how they utilize on-chip resources.

Block RAM (BRAM)

The device includes dedicated block RAM organized as 18 Kbit dual-port memories. These BRAMs can be configured as FIFOs, single-port RAM, or true dual-port RAM, which is particularly useful for buffering data streams in communications and video processing designs.

Digital Clock Managers (DCMs)

Two on-chip DCMs provide clock multiplication, division, deskewing, and phase shifting. This eliminates the need for external PLL circuits and helps designers close timing in complex synchronous designs.

I/O Architecture

With 124 user I/O pins across the 208-pin PQFP footprint, the XC3S50-4PQ208I supports multiple I/O standards including LVCMOS, LVTTL, SSTL, HSTL, and differential standards such as LVDS and BLVDS. This multi-standard I/O flexibility allows seamless interfacing to a wide range of memory, processor, and peripheral components.

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Speed Grade –4 Explained

The –4 speed grade is the fastest variant in the Spartan-3 XC3S50 lineup. A faster speed grade means:

• Lower propagation delays through logic and routing resources
• Higher achievable clock frequencies
• Better timing margin in performance-critical designs

For engineers with tight timing budgets — such as high-speed serial interfaces, DSP pipelines, or rapid prototyping of ASIC designs — selecting the –4 grade over the –5 (slower) variant can make the difference between meeting and missing timing closure.

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Industrial Temperature Rating: Why It Matters

The “I” suffix designates the industrial temperature range: –40°C to +100°C junction temperature. This rating ensures the device operates reliably across the following use cases:

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Typical Applications for the XC3S50-4PQ208I

The combination of 50K gates, 124 I/Os, block RAM, DCMs, and an industrial temperature rating makes the XC3S50-4PQ208I well-suited for:

• Broadband access equipment — line-side logic and protocol bridging
• Display and projection systems — pixel pipeline control and timing generation
• Consumer networking — packet classification and header processing
• Industrial control — state machine-based control logic, sensor interfaces
• Automotive electronics — body control modules, gateway logic
• Test and measurement — stimulus generation, data capture
• Communications — UART/SPI/I2C protocol bridges and glue logic

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Ordering Information & Part Number Comparison

The XC3S50 is available in several package and temperature variants. The table below shows the most common options to help engineers select the right part:

Choose the XC3S50-4PQ208I when you need maximum I/O count (124 pins) with industrial temperature assurance and the fastest speed grade in the through-hole-friendly PQFP footprint.

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Design Tools & Programming

The XC3S50-4PQ208I is supported by Xilinx ISE Design Suite (the legacy toolchain for Spartan-3 devices). Key tools include:

• ISE Project Navigator — RTL entry, synthesis, and implementation
• PlanAhead — floorplanning and timing analysis
• iMPACT — JTAG-based device configuration and boundary scan
• XPower Analyzer — power estimation and budgeting

Configuration is loaded via JTAG or an external SPI/parallel flash memory device. Bitstream size for the XC3S50 is approximately 439 Kbits.

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Frequently Asked Questions

Q: Is the XC3S50-4PQ208I RoHS compliant? A: No. The XC3S50-4PQ208I is a legacy device and is not RoHS compliant. Engineers designing new products for EU markets should evaluate whether the non-compliant finish (tin-lead) is acceptable or consider an alternative device.

Q: What is the difference between XC3S50-4PQ208I and XC3S50-4PQG208I? A: These part numbers refer to the same device. The “G” sometimes appears in distributor listings as a variant of the standard designation; both denote the same Spartan-3, 50K gate, 208-pin PQFP, industrial-grade FPGA.

Q: Can the XC3S50-4PQ208I be used in new designs? A: The Spartan-3 family is a mature product line. It remains suitable for replacement, repair, and legacy production. For new designs, Xilinx recommends more current families such as Spartan-7. However, the XC3S50-4PQ208I continues to be available through authorized distributors for existing design support.

Q: What configuration memory is compatible? A: The XC3S50-4PQ208I is compatible with Xilinx Platform Flash devices (XCF series) as well as third-party SPI and parallel NOR flash memory chips. Consult the Spartan-3 Configuration User Guide (UG332) for full details.

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Summary

The XC3S50-4PQ208I is a reliable, well-characterized Xilinx Spartan-3 FPGA delivering 50,000 gates, 1,728 logic cells, 124 I/Os, 72 Kbits of block RAM, and two digital clock managers — all in a 208-pin PQFP package rated for industrial temperatures. Its –4 speed grade ensures maximum timing performance, while the 90 nm process technology and 1.2 V core voltage keep power consumption low for embedded applications.