Gainsil Semiconductor Voltage References

Shunt (two-terminal) references operate like precision Zener diodes - they regulate voltage by drawing variable current. They require a series resistor to set operating current and are simpler but less efficient as they always draw quiescent current. Series (three-terminal) references act like linear regulators - they draw only the load current plus small quiescent current, making them more efficient. Series references offer better line regulation and lower output impedance. Shunt references are simpler, more flexible (can be used at any voltage with appropriate resistor), and often cheaper. Series references are preferred for battery-powered applications due to lower power consumption. Gainsil GS431 is a shunt reference

series references are available for higher performance applications.

Choose shunt references for simplicity and flexibility. Choose series references for lowest power consumption and best regulation.

Temperature drift error is calculated by multiplying the drift coefficient (ppm/°C) by the temperature range (°C) and the reference voltage. Error (V) = Vref × (Drift/1,000,000) × ΔT. For example, a 2.5V reference with 20ppm/°C drift over 100°C range has error: 2.5V × (20/1,000,000) × 100 = 5mV. This is 0.2% error from drift alone. Add initial accuracy error (±0.5% = ±12.5mV) for total error budget. For precision applications, choose lowest drift available (10ppm/°C or better). Consider your operating temperature range - industrial (-40°C to +85°C) has 125°C range

automotive (-40°C to +125°C) has 165°C range. Drift is not always linear - some references have specified drift over different temperature ranges.

Calculate total error including initial accuracy and drift over your temperature range. Choose lowest drift that meets your accuracy budget.

Voltage reference load capability depends on the specific device and configuration. Shunt references (GS431) can sink current from a few microamperes to tens of milliamperes depending on the series resistor and supply voltage. The series resistor sets maximum current: Imax = (Vsupply - Vref)/Rseries. Load current plus reference current must not exceed Imax. Series references typically source 5-20mA with minimal output voltage change. For higher currents, add an external buffer op-amp. The reference's output impedance determines load regulation - lower impedance means less voltage change with load current. For precision applications, minimize load current variations or buffer the reference output. Always verify load regulation specifications for your specific current requirements.

Calculate load requirements and verify reference can supply required current with acceptable regulation. Buffer with op-amp for high or variable loads.

ADC reference voltage selection involves several considerations. Match the reference to your ADC's full-scale input range for maximum utilization of ADC resolution. For a 3.3V system with 0-3.3V input range, use a 3.3V or 2.5V reference depending on ADC requirements. Higher reference voltages improve SNR but may exceed ADC limits. Verify the ADC's reference input requirements - some need specific voltages (2.048V, 2.5V, 4.096V, 5V). Consider your signal range - if signals are 0-2V, a 2.5V reference provides margin without wasting resolution. The reference voltage determines LSB (Least Significant Bit) size: LSB = Vref/2^n. For 12-bit ADC with 2.5V reference, LSB = 0.61mV. Choose reference accuracy and drift to support your measurement accuracy requirements.

Match reference voltage to ADC input range and signal levels. Verify ADC compatibility with chosen reference voltage.

Line regulation measures how much the reference output voltage changes when the input supply voltage varies. It's specified in ppm/V or μV/V. Good line regulation ensures reference stability despite supply variations from battery discharge, load transients, or power supply ripple. Shunt references have inherent line regulation determined by their dynamic impedance - typically 0.1-0.5Ω for good references. A 0.2Ω dynamic impedance with 1V supply change causes 0.2mV output change (80ppm for 2.5V reference). Series references typically have better line regulation (10-100ppm/V) due to their active regulation. For battery-powered applications where supply varies significantly, line regulation is critical. For mains-powered systems with good regulation, it may be less important.

For battery or poorly regulated supplies, choose references with good line regulation. Verify specifications against your expected supply variation.