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)

1. Disconnect FPGA (to avoid damage if power is faulty).

2. Measure voltages at all power rails using a DMM.

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

1. Check for oscillations with an oscilloscope.

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

C. Power-On Test (With FPGA Load)

1. Reconnect FPGA and power on.

2. Monitor voltage stability under load:

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

1. 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

1. Set voltage to expected rail value (e.g., 1.0V for VCCINT).
2. 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.