Digitally-controlled-voltage-reference

Description: This circuit demonstrates a straightforward approach to achieving a voltage reference that can be adjusted using an 8-bit Digital-to-Analog Converter (DAC) equipped with an integrated voltage reference. The analog output from the DAC controls the trim pin of the ZNREF025 through a resistor, Rs. When Rs equals 0, the circuit can yield a trim range exceeding ±5% of the nominal reference voltage. When Rs is greater than zero, the trim range decreases. It has been determined that to achieve a trim range reduced by half, the approximate value for Rs is around 1 MΩ. The reference voltage of the ZNREF025 can be set to an accuracy defined by the trim range of the device and the precision of the DAC. Increasing Rs diminishes the percentage trim range, thereby enhancing the effective voltage resolution. Alternative voltage references from the ZNREF series can be utilized in this circuit if different voltage levels are needed. This voltage reference can be employed to establish the value of VREF within a much tighter tolerance than the data sheet specification of ±1%, across a broader spectrum of operating conditions. Potential applications include systems that require automatic self-calibration of instrumentation, such as electronic weighing scales.

The circuit in question utilizes an 8-bit DAC to provide a precise voltage reference through the ZNREF025 voltage reference IC. This configuration allows for fine-tuning of the output voltage, making it suitable for applications that demand high accuracy. The resistor Rs plays a crucial role in defining the trim range; when Rs is set to 0, the circuit can achieve a wide trim range, providing flexibility in voltage adjustment. However, as Rs increases, the trim range narrows, which can be advantageous in scenarios where higher voltage resolution is necessary.

The ZNREF025 is designed to deliver stable reference voltages, and its integration with the DAC allows for dynamic adjustments. The accuracy of the reference voltage is contingent upon both the inherent precision of the DAC and the characteristics of the ZNREF025. By carefully selecting the value of Rs, the user can optimize the circuit for specific applications, balancing between trim range and voltage resolution.

This voltage reference circuit is particularly beneficial in systems requiring tight voltage tolerances, surpassing the standard ±1% specification. Its versatility makes it suitable for various applications, including precision instrumentation, sensor calibration, and electronic weighing systems, where consistent and reliable voltage references are critical for accurate measurements. The ability to adjust the reference voltage dynamically adds significant value in environments where conditions may vary, ensuring that the system maintains its accuracy and performance over a wide range of operating scenarios.This circuit shows a simple method of achieving a voltage reference which can be trimmed using an 8bit DAC with an on-chip voltage reference. The analogue output from the DAC drives the trim pin of the ZNREF025 via a resistor, R,. When Rs = 0, this circuit will produce a trim range exceeding ± 5% of the nominal reference voltage.

When Rs is greater than zero, the trim range is reduced. It was found that after dividing the trim range by two, the needed value for Rs was approximately 1 MO. The reference voltage of the ZNREF025 can be set to an accuracy determi11ed by the trim range of the device itself and the accuracy of the DAC. Increasing Rs reduces the percentage trim range and hence increases the effective voltage resolution.

Other voltage references from the ZNREF series can be used with this circuit if other voltages are required. This voltage reference can be used to set the value of VREF to a much tighter tolerance, than the data sheet specification of ±1%, in a much wider range of operating conditions.

Applications could include any system with automatic self-cahbration of instrumentation, such as in electronic weighing scales.