Gravity: GP8630N DAC Module Accuracy Test Report

This report documents the laboratory-verified performance of the Gravity: GP8630N 16-bit DAC module. All data analysis is based on raw output measurements without any software smoothing applied.

Final Testing Conclusions:

• Voltage Mode (0-12V): Exceptionally high accuracy. The maximum full-scale error is only 0.036% (at 12V), significantly outperforming the standard industrial requirement of 0.1%.
• Current Mode (0-24mA): Highly reliable. The maximum full-scale error for uncalibrated output is 0.34% (at 20mA). With the provided calibration coefficients, accuracy can be further optimized to <0.05%.

I2C Interface Performance Test

1.1 Voltage Output Mode Test (0-12V)

Test Conditions:

• Power Supply: 5.0V DC
• Input Protocol: I2C (16-bit)
• Full-Scale Range (FSR) Reference: 12.00 V

Measurement Data & Accuracy Analysis

1.2 Performance Conclusion

The module demonstrates industrial-grade linearity out of the box. The maximum deviation across the entire 12V range is merely ~6mV, ensuring precise control for VFDs (Variable Frequency Drives) and analog actuators without the need for user calibration.

1.3 Current Output Mode Test (0-24mA)

Test Conditions:

• Mode: 0-24mA Output Mode
• Full-Scale Range (FSR) Reference: 24.00 mA (Hardware Limit)

Pre-Calibration Data

*Note: This test focuses on the standard industrial 0-20mA range. The full-scale error percentage is calculated based on the hardware's 24mA maximum capability (FSR) to reflect the device's inherent accuracy ($Error / 24mA \times 100$).

Calibration Recommendations

The uncalibrated error of 0.34% is suitable for general-purpose applications. For precision instruments requiring <0.1% accuracy, applying the following linear correction in the microcontroller code is recommended:

• Formula: DAC_Value_Corrected = (Target_Value - Offset) / Coefficient
• Coefficient (c): 0.996993
• Offset (o): -14.54 (LSB)

PWM Interface Performance Test

Test Background

Although I2C provides the highest resolution (16-bit), PWM is widely utilized due to its simplicity and compatibility with legacy controllers. This test verifies the linearity of the GP8630N's internal PWM processing engine.

Test Conditions

• Input Signal: PWM (Recommended frequency 1kHz - 10kHz)
• Resolution: 10-bit (0 - 1023 duty cycle steps)
• Test Mode: 0-12V Voltage Output & 0-24mA Current Output
• Full-Scale Range (FSR): 12V (Voltage), 24mA (Current)

2.1 PWM Voltage Mode (0-12V)

Measurement Data

Performance Analysis

• Linearity Assessment: The PWM voltage mode exhibits excellent linearity across the full scale, with all measurement points falling within ±0.08V of the target. The maximum full-scale error is 0.06% (at the 256 and 512 points), strictly complying with the 0.1% industrial tolerance.
• Key Observation: A slight systematic negative deviation was observed in the mid-range (25%-50% duty cycle), where the output consistently remained 7-8mV below the target. This characteristic is stable and predictable; if accuracy below 0.05% is required, it can be easily compensated via linear calibration.
• Conclusion: The PWM voltage decoding of the GP8630N achieves industrial-grade accuracy without calibration. The native performance is entirely sufficient for most VFD control and analog driving applications. Its internal DAC logic significantly outperforms traditional RC filter-based PWM-to-analog converters.

2.2 PWM Current Mode (0-24mA)

Measurement Data

*Note: Full-scale error is calculated based on the 24mA hardware maximum range.

Performance Analysis

• Outstanding Mid-Range Accuracy: The 6mA test point (25% duty cycle) demonstrates extremely high accuracy with an error of only +0.0002mA (+0.001% FS). This level of precision, verified against a dedicated 16-bit DAC, confirms the high quality of the module's internal signal processing.
• Full-Scale Characteristics: The error gradually increases towards the higher end, reaching +0.50% at 24mA. This is a typical trait of current-mode DACs and remains within an acceptable range for industrial 4-20mA applications.
• Important Notice - Low-Current Anomaly: Testing revealed a notably higher error (+0.57%) at the 2mA point (not shown in the main table). Users requiring guaranteed accuracy at extremely low currents (<4mA) should verify the performance in their specific application or consider utilizing the 4-20mA range to bypass this anomaly.

Calibration Recommendations

For applications requiring <0.1% accuracy across the entire 0-24mA range:

• Formula: DAC_Value_Corrected = (Target_Value - Offset) / Coefficient
• Coefficient (c): 1.000376
• Offset (o): -1.68 (LSB)

Through calibration, the maximum error in the 4-24mA range can be reduced to <0.05%.

• Non-Calibrated Use Cases:
• General industrial control: 0-20mA range (Error <0.3%)
• Standard 4-20mA instrumentation: 4-20mA range (Error <0.25%)
• Precision applications: Calibration required

Comparison: I2C vs. PWM Performance

Mode Selection Guide

When to Choose I2C Mode:

• Requires maximum precision (±0.04%)
• Requires high resolution (16-bit)
• Capable of fast digital communication
• Multiple devices sharing the same bus

When to Choose PWM Mode:

• Interfacing with legacy PLCs or microcontrollers
• Simple wiring preferred (single signal line)
• 10-bit resolution is sufficient for the application
• Need compatibility with existing PWM control systems

Comprehensive Evaluation of PWM Performance

The PWM interface of the GP8630N is not merely a fallback feature—it delivers genuine industrial-grade performance, surpassing many dedicated PWM-input DACs on the market.

Key Advantages:

• Voltage Mode: Achieves a clean ±0.06% accuracy without calibration.
• Exceptional Mid-Range Performance: The 0.001% error at the 6mA point demonstrates superior internal processing capabilities.
• Predictable Behavior: Systematic error patterns make calibration highly effective.
• True Digital Decoding: Vastly superior to passive RC filtering methods.

Considerations:

• Slightly higher error at full-scale current (0.50%); precision work requires calibration.
• Specific applications should note the low-current anomaly at 2mA.
• The 10-bit resolution limits fine-tuning capabilities compared to the 16-bit I2C.

For applications that do not mandate sub-0.1% accuracy or ultra-fine resolution, the PWM mode offers a robust, straightforward, and reliable control interface. The module's internal digital processing ensures performance consistency unmatched by traditional analog PWM-DAC solutions.

Summary: GP8630N Complete Performance Overview

Module Positioning:

The GP8630N is a dual-interface precision DAC that bridges the gap between laboratory-grade precision and industrial-grade robustness. Whether controlled via I2C for maximum accuracy or via PWM for maximum compatibility, it delivers consistent, linear performance tailored for professional applications.