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HI51's avatar
HI51
Icon for New Contributor rankNew Contributor
3 months ago

Agilex5のVREFP_ADCについて

Agilex5のVREFP_ADCについて高精度なADCの精度を求める場合は1.25Vの電圧を入力するとのことですが、この端子に流れる電流はどれくらいになりますでしょうか？ 精度が高い1.25Vを供給できる部品でコスト面でよいものがないので、他の電圧からの抵抗分割（数kΩ）で供給できればと考えていますが、流れる電流によっては使えない方法かと思っています。
Farabi's avatar
Farabi
Icon for Regular Contributor rankRegular Contributor
2 months ago

Hello,


To achieve high-precision ADC performance on Agilex 5, Intel recommends supplying 1.25V reference voltage to VREFP_ADC pin. However, the current drawn by this pin is not explicitly stated in the datasheet.


Typically, FPGA ADC reference inputs like VREFP_ADC are designed as high-impedance inputs, meaning they draw very little current- usually in the range of microamperes(uA). This allows external precision voltage sources to drive the pin without significant loading.


Regarding using resistor divider for 1.25V, only suitable for below conditions :

1- VREFP_ADC has high input impedance

2- output impedance of the divider is low enough to maintain voltage stability.

3- your design includes an op-amp to prevent voltage sag due to load changes or noise.


You may want consider below alternatives:

1- Low-cost precision voltage reference ICs eg. TI REF3312, or Analog Device ADR125 etc.

2- Resistor divider + Op-amp buffer implementation.


regards,

Farabi