The XC3S400-4FTG256I is a high-performance field-programmable gate array (FPGA) from the Xilinx Spartan-3 family, now manufactured under AMD. Designed for cost-sensitive, high-volume applications, this industrial-grade device delivers 400,000 system gates in a compact 256-ball Fine-pitch Ball Grid Array (FTBGA) package. Whether you are developing embedded systems, industrial control solutions, or digital signal processing applications, the XC3S400-4FTG256I offers an ideal balance of logic density, I/O flexibility, and power efficiency.
This guide covers the full technical specifications, key features, pinout details, application use cases, and ordering information for the XC3S400-4FTG256I FPGA.
What Is the XC3S400-4FTG256I?
The XC3S400-4FTG256I belongs to Xilinx’s Spartan-3 FPGA series — one of the most widely deployed low-cost FPGA platforms in the world. The part number breaks down as follows:
| Part Number Segment |
Meaning |
| XC3S |
Xilinx Spartan-3 family |
| 400 |
400,000 system gates |
| -4 |
Speed grade –4 (slowest/lowest power) |
| FTG |
Fine-pitch Ball Grid Array (FTBGA) package |
| 256 |
256 ball package |
| I |
Industrial temperature range (–40°C to +100°C) |
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XC3S400-4FTG256I Key Specifications
General Electrical Characteristics
| Parameter |
Value |
| Manufacturer |
AMD (Xilinx) |
| Part Number |
XC3S400-4FTG256I |
| Series |
Spartan-3 |
| Logic Cells |
8,064 |
| System Gates |
400,000 |
| CLB Array |
56 × 72 (Slices) |
| Total Slices |
3,584 |
| Flip-Flops |
7,168 |
| Maximum Distributed RAM |
56 Kb |
| Block RAM |
288 Kb (16 × 18 Kb RAMs) |
| Multipliers (18×18 bit) |
16 |
| DCMs (Digital Clock Managers) |
4 |
| Maximum User I/O Pins |
141 |
| Supply Voltage (VCC INT) |
1.2V |
| Supply Voltage (VCC AUX) |
2.5V |
| Supply Voltage (VCC IO) |
1.2V – 3.3V |
Package and Physical Characteristics
| Parameter |
Value |
| Package Type |
FTBGA (Fine-pitch Thin Ball Grid Array) |
| Package Code |
FTG256 |
| Ball Count |
256 |
| Body Size |
17 mm × 17 mm |
| Ball Pitch |
1.0 mm |
| Height (Max) |
1.55 mm |
| RoHS Compliance |
Yes |
| MSL (Moisture Sensitivity Level) |
MSL 3 |
Speed and Timing Characteristics
| Parameter |
Value |
| Speed Grade |
–4 |
| Maximum Clock Frequency |
Up to 280 MHz (logic dependent) |
| DCM Clock Jitter |
< 300 ps (typical) |
| Input Setup Time |
Dependent on I/O standard |
| Operating Conditions |
Industrial |
Environmental and Thermal Ratings
| Parameter |
Value |
| Temperature Grade |
Industrial (I) |
| Operating Temperature Range |
–40°C to +100°C |
| Junction Temperature (Tj Max) |
125°C |
| Thermal Resistance (θJA) |
~23°C/W (still air, 256-ball BGA) |
| Storage Temperature |
–65°C to +150°C |
| ESD Rating |
Human Body Model: 2,000V |
XC3S400-4FTG256I Pin Configuration Overview
The XC3S400-4FTG256I uses a 256-ball FTBGA footprint arranged in a 16×16 grid with 1.0 mm ball pitch. The pin assignments include the following functional groups:
I/O Bank Summary
| I/O Bank |
Number of User I/O |
Supported I/O Standards |
| Bank 0 |
Up to 34 |
LVCMOS, LVTTL, SSTL, HSTL |
| Bank 1 |
Up to 35 |
LVCMOS, LVTTL, SSTL, HSTL |
| Bank 2 |
Up to 36 |
LVCMOS, LVTTL, SSTL, HSTL |
| Bank 3 |
Up to 36 |
LVCMOS, LVTTL, SSTL, HSTL |
Supported I/O Standards
The XC3S400-4FTG256I supports a broad set of single-ended and differential I/O standards:
| Standard Type |
Supported Standards |
| Single-Ended |
LVCMOS 3.3V/2.5V/1.8V/1.5V/1.2V, LVTTL |
| Source-Synchronous |
SSTL2 Class I/II, SSTL3 Class I/II |
| Low Voltage Differential |
LVDS, LVPECL, LDT (HyperTransport) |
| High-Speed Transceiver Logic |
HSTL Class I/II |
XC3S400-4FTG256I Architecture Deep Dive
Configurable Logic Blocks (CLBs)
The core logic fabric of the XC3S400-4FTG256I is built around 3,584 slices, each containing two 4-input Look-Up Tables (LUTs) and two flip-flops. Each LUT can be used as a 16×1-bit synchronous RAM or 16-bit shift register (SRL16), offering significant flexibility for both logic and memory-intensive designs.
Block RAM (BRAM)
Sixteen 18 Kb dual-port block RAMs provide a total of 288 Kb of on-chip memory. These are ideal for implementing FIFOs, line buffers, lookup tables, and local data storage in embedded processor systems. Each BRAM can be independently configured for different data widths and port modes.
Digital Clock Managers (DCMs)
Four integrated DCMs enable advanced clocking strategies including:
- Frequency synthesis (DLL-based multiplication and division)
- Phase shifting (fine and coarse)
- Clock skew elimination
- Deskew up to 256 steps
Multiplier Blocks
Sixteen dedicated 18×18-bit multiplier blocks enable efficient DSP and signal processing pipelines without consuming CLB resources. These are useful for filtering, FFT engines, and arithmetic-intensive compute kernels.
XC3S400-4FTG256I vs Comparable Spartan-3 Devices
| Feature |
XC3S200 |
XC3S400 |
XC3S1000 |
| System Gates |
200K |
400K |
1,000K |
| Slices |
1,920 |
3,584 |
7,680 |
| Block RAM (Kb) |
216 |
288 |
432 |
| Multipliers |
12 |
16 |
24 |
| DCMs |
4 |
4 |
4 |
| Max User I/O (FTG256) |
141 |
141 |
N/A |
The XC3S400 hits a sweet spot between the entry-level XC3S200 and the larger XC3S1000, offering substantially more logic density and embedded RAM while remaining in the same compact FTG256 package.
XC3S400-4FTG256I Configuration and Programming
Configuration Modes
The XC3S400-4FTG256I supports multiple configuration interfaces to suit different board topologies:
| Configuration Mode |
Description |
| Master Serial |
FPGA loads bitstream from serial PROM |
| Slave Serial |
External controller drives configuration |
| Master Parallel (SelectMAP) |
Fast parallel configuration interface |
| Slave Parallel (SelectMAP) |
Controlled parallel loading |
| JTAG (IEEE 1149.1) |
Boundary scan and in-system programming |
Bitstream and Configuration Memory
The configuration bitstream size for XC3S400 is approximately 1,699,136 bits (~212 KB). Compatible configuration PROMs include Xilinx XCF family serial flash devices and standard SPI/BPI NOR flash components.
XC3S400-4FTG256I: Target Applications
The XC3S400-4FTG256I industrial temperature rating and robust I/O capabilities make it ideal for demanding real-world deployments:
Industrial Automation and Control
- PLC (Programmable Logic Controller) co-processing
- Motor drive control and encoder feedback interfaces
- Industrial Ethernet (EtherCAT, PROFINET) bridging
- Safety-critical digital I/O expansion
Embedded Systems and SoC Designs
- MicroBlaze soft-processor-based embedded designs
- Custom bus bridging (AHB, APB, Wishbone)
- Peripheral expansion for microcontrollers
Communications and Networking
- Serial protocol bridging (UART, SPI, I2C, CAN)
- Multi-channel data aggregation
- Video and image processing pipelines (SD resolution)
Test and Measurement Equipment
- Pattern generation and capture
- Protocol analyzers
- High-speed digitizer front-ends
Military and Defense (COTS)
The industrial (I-grade) temperature range of –40°C to +100°C satisfies many COTS (Commercial Off-The-Shelf) military and avionics system requirements where extended temperature operation is needed.
XC3S400-4FTG256I Design Tools and IP Support
Xilinx ISE Design Suite
The XC3S400-4FTG256I is fully supported by the Xilinx ISE Design Suite (the legacy toolchain for Spartan-3 devices). Key tool components include:
| Tool |
Purpose |
| ISE Project Navigator |
RTL design entry, synthesis, P&R |
| XST (Xilinx Synthesis Technology) |
HDL synthesis (VHDL/Verilog) |
| ISim / ModelSim |
Behavioral and timing simulation |
| iMPACT |
JTAG configuration and programming |
| ChipScope Pro |
In-system logic analyzer |
| CORE Generator |
Parameterized IP core instantiation |
Note: ISE 14.7 is the final version supporting Spartan-3. It is available as a free download from the AMD/Xilinx website for legacy support.
MicroBlaze Soft Processor Support
The XC3S400 can comfortably host a MicroBlaze 32-bit soft processor core with minimal peripherals at up to ~75–100 MHz, enabling full embedded software development with the Xilinx EDK (Embedded Development Kit).
Ordering Information
XC3S400-4FTG256I Part Number Breakdown
| Field |
Code |
Meaning |
| Family |
XC3S |
Spartan-3 |
| Density |
400 |
400K system gates |
| Speed Grade |
-4 |
Standard speed, lower power |
| Package |
FTG |
Fine-pitch Thin BGA |
| Pin Count |
256 |
256-ball package |
| Temp Grade |
I |
Industrial (–40°C to +100°C) |
Alternative Part Numbers and Variants
| Part Number |
Speed Grade |
Temp Grade |
Package |
| XC3S400-4FTG256C |
–4 |
Commercial (0°C to +85°C) |
FTG256 |
| XC3S400-4FTG256I |
–4 |
Industrial (–40°C to +100°C) |
FTG256 |
| XC3S400-5FTG256I |
–5 |
Industrial |
FTG256 |
| XC3S400-4PQ208I |
–4 |
Industrial |
PQ208 (PQFP) |
| XC3S400-4TQ144I |
–4 |
Industrial |
TQ144 (TQFP) |
XC3S400-4FTG256I PCB Design Considerations
Power Supply Decoupling
For reliable operation, proper decoupling of the three power rails is essential:
| Rail |
Voltage |
Recommended Capacitance per Pin |
| VCCINT (Core) |
1.2V |
100 nF ceramic (X5R/X7R) |
| VCCAUX (Auxiliary) |
2.5V |
100 nF ceramic |
| VCCIO (I/O banks) |
1.2V – 3.3V |
100 nF per I/O power pin |
BGA Soldering and Land Pattern
| Parameter |
Value |
| Land Diameter |
0.55 mm (SMD pad) |
| Solder Mask Opening |
0.50 mm |
| Solder Ball Diameter |
0.5 mm (Ni/Au plated Cu) |
| Recommended Reflow Profile |
Lead-Free SAC305 |
| X-ray Inspection |
Strongly recommended for BGA |
Frequently Asked Questions (FAQ)
Q: Is the XC3S400-4FTG256I RoHS compliant? Yes. The XC3S400-4FTG256I is fully RoHS compliant and ships in lead-free packaging.
Q: What is the difference between the -4 and -5 speed grades? The –5 speed grade offers faster timing performance (lower propagation delays, higher maximum clock frequency) compared to –4. For most cost-sensitive designs, –4 provides adequate performance.
Q: Can the XC3S400-4FTG256I be used in aerospace applications? The I-grade device meets many COTS aerospace requirements. For full military qualification (QML, MIL-PRF-38535), consult AMD/Xilinx for radiation-hardened or space-grade alternatives.
Q: What configuration PROM is compatible with the XC3S400? Recommended PROMs include the XCF04S (4 Mbit, 1.8V/3.3V serial flash) and standard 4 Mbit SPI NOR flash devices such as the M25P40 or AT25DF041A.
Q: Is JTAG boundary scan supported? Yes. The XC3S400-4FTG256I includes full IEEE 1149.1 JTAG support for boundary scan testing and in-system programming via iMPACT.
Summary
The XC3S400-4FTG256I is a well-established, cost-effective FPGA solution ideally suited for industrial-grade embedded, control, and communications applications. With 400K system gates, 288 Kb of block RAM, 16 hardware multipliers, 4 DCMs, and up to 141 user I/O pins in a compact 17×17 mm BGA package, it offers a powerful logic density in a proven platform backed by the full Xilinx Spartan-3 design ecosystem.
Its industrial temperature rating (–40°C to +100°C) makes it a reliable choice wherever standard commercial-grade parts cannot meet thermal requirements — from factory floor automation to outdoor telecommunications infrastructure.
