Precision Voltage References

What is a Precision Voltage Reference?

  • Very high initial accuracy and low noise
  • Flexibility: many voltage options and small packaging
  • Good line and load regulation performances
  • Line regulation is a measure of how well a circuit maintains its output voltage with respect to changing input voltage. It's defined as:
    • ΔVout/ΔVin
  • Load regulation is a measure of how well a circuit maintains its output voltage with respect to changing load conditions. It's defined as:
    • ΔVout/ΔIout

Applications that require precision voltage reference:

The figure below shows a precision voltage reference used in an ADC application.

adc-voltage-reference.png

Why Should I Use a Precision Voltage Reference?

Accuracy
An Analog–to–Digital Converter's (ADC's) performance is affected by the voltage reference as the ADC Code is inversely proportional to the voltage reference:

For example, the LSB for a 16-bit ADC with VREF = 4.096 V is 62.5 µV

Using a voltage reference with tight initial error can help eliminate room-temperature systems calibration. Voltage reference performance affects an ADC’s overall accuracy. Using a voltage reference with tight initial error can help eliminate room-temperature systems calibration.

Output Noise
Output noise should be smaller than the least significant bit (LSB) voltage (the minimum change in voltage that causes a change in the output code) to maintain converter accuracy.

MCP1501 High-Precision Buffered Voltage Reference Key Features:

  • Initial accuracy: 0.08%
  • Temperature coefficient:
    • 210 ppm/°C typical and 50 ppm/°C max
  • Line regulation: 50 ppm/V
  • Load regulation: 40-70 ppm/mA
  • Output noise: <20 µVp-p
  • 8 voltage options: 1.024 V, 1.25 V, 1.8 V, 2.048 V, 2.5 V, 3 V, 3.3 V, 4.096 V
  • Operating current: 140 µA
  • Extended temperature range: -40 °C to +125 °C
  • Packages: Very small 8L 2x2 WDFN, 6L SOT-23, 8L SOIC

Figure below shows a basic MCP1501 circuit configuration. The input voltage is connected to the device at the VIN input, with an optional 2.2 μF ceramic capacitor. This capacitor would be required if the input voltage has excess noise. A 2.2 μF capacitor would reject input voltage noise at approximately 1 to 2 MHz. Noise below this frequency will be amply rejected by the input voltage rejection of the voltage reference. Noise at frequencies above 2 MHz will be beyond the bandwidth of the voltage reference and, consequently, not transmitted from the input pin through the device to the output.

mcp1501.PNG

PIN FUNCTION TABLE

Function Symbol
Buffered VREF output OUT
Buffered VREF feedback FEEDBACK
System ground GND
Shutdown Pin Active low SHDN Bar
Power Supply input VDD
Exposed thermal pad EP

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