How to Test the Power Supply of an FPGA

Testing an FPGA's power supply is critical to ensure stable operation, avoid damage, and prevent erratic behavior. Below is a step-by-step guide covering measurement techniques, tools, and common issues. 1. Key Power Supply Requirements FPGAs typically require: Core Voltage (VCCINT) – Low voltage (e.g., 0.9V, 1.0V) for internal logic. I/O Voltage (VCCIO) – Higher voltage (e.g., 1.2V, 1.8V, 3.3V) for interfacing. Auxiliary Voltage (VCCAUX, VCCBRAM) – For PLLs, block RAM, etc. Example (Xilinx Artix-7): Rail Typical Voltage Tolerance VCCINT 1.0V ±3% VCCIO 3.3V ±5% VCCAUX 1.8V ±5% 2. Tools Needed 3. Step-by-Step Testing Procedure A. Visual Inspection Check for short circuits, cold solder joints, or damaged capacitors. Verify polarity of electrolytic capacitors. B. Power-On Test (No FPGA Load) Disconnect FPGA (to avoid damage if power is faulty). Measure voltages at all power rails using a DMM. Confirm they match expected values (e.g., 1.0V, 3.3V). Check for oscillations with an oscilloscope. Acceptable ripple: Typically

Apr 8, 2025 - 09:46

Testing an FPGA's power supply is critical to ensure stable operation, avoid damage, and prevent erratic behavior. Below is a step-by-step guide covering measurement techniques, tools, and common issues.

1. Key Power Supply Requirements
FPGAs typically require:

Core Voltage (VCCINT) – Low voltage (e.g., 0.9V, 1.0V) for internal logic.
I/O Voltage (VCCIO) – Higher voltage (e.g., 1.2V, 1.8V, 3.3V) for interfacing.
Auxiliary Voltage (VCCAUX, VCCBRAM) – For PLLs, block RAM, etc.

Example (Xilinx Artix-7):

Rail Typical Voltage Tolerance
VCCINT 1.0V ±3%
VCCIO 3.3V ±5%
VCCAUX 1.8V ±5%

2. Tools Needed

3. Step-by-Step Testing Procedure
A. Visual Inspection

Check for short circuits, cold solder joints, or damaged capacitors.
Verify polarity of electrolytic capacitors.

B. Power-On Test (No FPGA Load)

Disconnect FPGA (to avoid damage if power is faulty).
Measure voltages at all power rails using a DMM.

Confirm they match expected values (e.g., 1.0V, 3.3V).

Check for oscillations with an oscilloscope.

Acceptable ripple: Typically <50mV for core, <100mV for I/O.

C. Power-On Test (With FPGA Load)

Reconnect FPGA and power on.
Monitor voltage stability under load:

Use a scope to check for droops or spikes during FPGA startup.

Measure current with a DMM (if possible) or a shunt resistor.

D. Dynamic Load Testing
Run a high-load FPGA design (e.g., logic-heavy test).

Monitor:

Voltage dips during high switching activity.
Temperature rise in regulators and FPGA.

E. Noise & Ripple Analysis

Use oscilloscope in AC coupling mode.
Bandwidth limit: 20MHz (to filter high-frequency noise).
Probe properly (use short ground springs, not long leads).

4. Common Power Issues & Fixes

5. Advanced Testing (Optional)
A. Power Sequencing Verification

Some FPGAs require specific power-up order (e.g., core before I/O).
Use a scope to track ramp-up timing.

B. Inrush Current Measurement

Current probe or shunt resistor + scope.
Ensure inrush doesn’t exceed regulator limits.

C. Long-Term Stability Test

Run FPGA at full load for hours.
Log voltage, current, and temperature trends.

6. Example Test Setup
Using a Bench Power Supply

Set voltage to expected rail value (e.g., 1.0V for VCCINT).
Gradually increase current limit while monitoring behavior.

Using a Multimeter & Scope

FPGA Board
├── VCCINT → DMM/O-scope probe
├── VCCIO → DMM/O-scope probe
└── GND → Scope ground

7. Safety Tips

Double-check polarity before powering.
Start with low current limits to avoid damage.
Use isolation if probing high-voltage circuits.

Conclusion

Test power rails before FPGA connection (no-load check).
Verify voltage, ripple, and sequencing under load.
Fix issues early (decoupling, regulator selection).
Use an oscilloscope for dynamic behavior analysis.