For embedded systems engineers and hardware designers, the Xilinx (now AMD) Spartan-3E family remains a legendary choice for cost-sensitive applications. Among this family, the XC3S250E-4FT256C stands out as a balanced solution, offering substantial logic density in a compact Fine-Pitch Ball Grid Array (FTBGA) package.
Whether you are maintaining legacy industrial equipment or designing a cost-effective DSP module, understanding the specific attributes of this chip is crucial. This guide provides a deep dive into the datasheet specifications, pinout configurations, and programming workflows for the XC3S250E-4FT256C.
Table of Contents
- XC3S250E-4FT256C Datasheet & Key Specifications
- FT256 Package Pinout & PCB Design
- Spartan-3E Architecture & Performance Analysis
- Programming Guide & Development Tools
- Conclusion
XC3S250E-4FT256C Datasheet & Key Specifications
The XC3S250E-4FT256C is designed for high-volume consumer electronics, automotive networking, and industrial control. The part number itself reveals its key operating parameters:
- XC3S250E: Spartan-3E family with 250,000 System Gates.
- -4: Standard Speed Grade.
- FT256: 256-ball Fine-Pitch Thin BGA package (17 x 17 mm).
- C: Commercial Temperature Range (0°C to 85°C).
Specification Summary Table
| Feature | Specification |
|---|---|
| Logic Cells | 5,508 |
| System Gates | 250K |
| CLB Array | 34 Rows x 26 Columns |
| Total Block RAM | 216 Kbits |
| Distributed RAM | 38 Kbits |
| DCMs (Digital Clock Managers) | 4 |
| User I/O (Max) | 172 |
| Core Voltage ($V_{CCINT}$) | 1.2V |
Price Analysis & Market Availability
While newer series like the Spartan-6 or Artix-7 offer higher performance, the XC3S250E remains vital for existing designs. Due to its "Legacy" status, sourcing authentic components can be challenging.
Note: Sourcing obsolete or legacy FPGAs requires a trusted supply chain partner to avoid counterfeit chips. [Check Stock for XC3S250E-4FT256C at Aichiplink] to view real-time inventory from verified distributors.
Alternatives & Replacement Parts
If the XC3S250E-4FT256C is unavailable, engineers often look at:
- XC3S250E-4PQ208C: Same silicon, different package (Plastic Quad Flat Pack) – easier to solder manually but larger footprint.
- XC3S500E-4FT256C: Same package, higher density (see comparison below).
FT256 Package Pinout & PCB Design
The FT256 package is a 1.00 mm pitch BGA, ideal for saving board space. However, it requires precise PCB layout strategies.
FT256 BGA Footprint & Dimensions
Designing the land pattern for the FT256 requires attention to the NSMD (Non-Solder Mask Defined) pads to ensure reliable solder joints.
- Ball Pitch: 1.00 mm.
- Array: 16 x 16 grid.
- Body Size: 17mm x 17mm.
Schematic Symbol Integration
When creating your schematic symbol (in Altium, KiCad, or OrCAD), note that the Spartan-3E I/Os are divided into 4 Banks:
- Bank 0 & 1: Top and Right.
- Bank 2 & 3: Bottom and Left.
- Important: Each bank can support different I/O standards (e.g., LVCMOS 3.3V, 2.5V, LVDS) based on the $V_{CCO}$ applied to that bank.
BGA Reflow Soldering Temperature Guide
For the XC3S250E-4FT256C, a standard lead-free reflow profile is recommended if using RoHS compliant parts:
- Peak Temperature: 245°C - 260°C.
- Time Above Liquidus (217°C): 60-150 seconds.
- Ramp Rate: Max 3°C/second.
Spartan-3E Architecture & Performance Analysis
The architecture of the XC3S250E is optimized for logic-heavy applications rather than memory-intensive ones.
Comparison: XC3S250E vs. XC3S500E
A common question during selection is whether to upgrade to the 500E.
| Feature | XC3S250E | XC3S500E | Difference |
|---|---|---|---|
| System Gates | 250K | 500K | Double capacity |
| Logic Cells | 5,508 | 10,476 | ~90% increase |
| Block RAM | 216K | 360K | Significant increase |
| Package Compatibility | FT256 Available | FT256 Available | Pin-compatible |
Insight: Since they share the FT256 footprint, you can often design the PCB for the XC3S500E and populate it with the XC3S250E to save costs if the logic fits.
Power Consumption & Thermal Management
The XC3S250E operates at a core voltage of 1.2V. Static power is relatively low, but dynamic power scales linearly with clock frequency.
- Quiescent Power: Typically < 50mW at 25°C.
- Requirement: A robust power distribution network (PDN) with bypass capacitors close to the BGA balls is essential to handle current transients.
Programming Guide & Development Tools
Configuring the Spartan-3E requires specific legacy tools, as it is not supported by the modern Vivado Design Suite.
Using Xilinx ISE WebPACK with Spartan-3E
To develop for the XC3S250E, you must use Xilinx ISE Design Suite.
- Recommended Version: ISE 14.7 (Windows 10 version requires a VM workaround usually provided by Xilinx).
- License: The "WebPACK" license is free and covers the XC3S250E device.
JTAG Configuration Circuit Design
The most common method for debugging and programming is JTAG.
- Pin Connections: Connect TCK, TMS, TDI, and TDO to a 14-pin or 10-pin JTAG header.
- Pull-ups: Ensure TCK, TMS, and TDI have internal or external pull-up resistors to $V_{CCAUX}$ (2.5V).
- Mode Pins: For dedicated JTAG configuration, set Mode Pins (M0, M1, M2) to
1:0:1.
Recommended Development Boards
For prototyping, looking for boards like the Digilent Basys 2 (legacy) or generic "Spartan-3E Starter Boards" on the secondary market is common. These boards typically feature the XC3S250E or 500E and break out the I/Os to expansion headers.
Conclusion
The XC3S250E-4FT256C remains a workhorse in the FPGA world, offering a perfect balance of I/O count, logic density, and physical size. Whether you are designing a new custom PCB or repairing a legacy system, understanding its pinout and power requirements is key to success.
Ready to start your design?
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Frequently Asked Questions
Is the XC3S250E-4FT256C 5V tolerant?
No, the Spartan-3E inputs are **not directly 5V tolerant**. The maximum DC voltage overshoot is typically limited to $V_{CCO} + 0.5V$. To interface with 5V legacy logic (such as older microcontrollers), you must use voltage level translators or current-limiting series resistors to utilize the internal PCI clamp diodes effectively.
Can I use Xilinx Vivado to program this chip?
No. The Spartan-3E family is a legacy architecture and is **not supported by the modern Vivado Design Suite**. You must use the **Xilinx ISE Design Suite (version 14.7)**. Note that on Windows 10 or 11 systems, you may need to run the ISE 14.7 VM (Virtual Machine) version for stability.
Which external configuration memory is recommended?
Since the XC3S250E is SRAM-based (volatile), it loses its configuration when powered down. Standard solutions include: * **Xilinx Platform Flash**: XCF02S (2 Mbit) or XCF04S. * **SPI Serial Flash**: Industry-standard SPI flash memories (e.g., M25P series), which are often more cost-effective and space-saving.
What does the "-4" speed grade mean?
The "-4" denotes the **Standard Performance** speed grade. Xilinx Spartan-3E chips were typically available in -4 (Standard) and -5 (High Performance). The -4 grade is sufficient for most general-purpose applications, supporting system clock rates up to approximately 200-250 MHz depending on the logic design complexity.
What are the critical power-on sequencing requirements?
To ensure proper initialization, the Spartan-3E requires a specific power rail sequence: **$V_{CCINT}$ (1.2V)** should ramp up first, followed by **$V_{CCAUX}$ (2.5V)**, and finally **$V_{CCO}$ (3.3V/2.5V)**. While the chip is robust, failing to follow this sequence (or simultaneous ramping) can sometimes cause configuration failures or high inrush currents.
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