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FM4 ADC Usage Hardware Consideration - KBA227596

FM4 ADC Usage Hardware Consideration - KBA227596

ChaitanyaV_61
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Author: TakashiM_61           Version: **

Translation - Japanese: FM4 ADCの使用上、ハードウエアの懸念点‐KBA227596- Community Translated (JA)

Question:

What is the hardware consideration to use ADC in FM4 device?

Answer:
In order to use ADC properly, the reference voltage (Analog Voltage Reference High (AVRH) /Analog Voltage Reference Low (AVRL)) are important. It is necessary to suppress the reference voltage swing and avoid noise on power and ground lines as much as possible.

From schematic/circuit observation, the following points must be considered:

  • AVRH / AVRL
    • AVRH-C Bypass capacitor “0.1 μF” is connected between AVRH and AVRL lines.
    • AVRH-R Register “3.3Ω” is populated on AVRH line. This is to make high frequency noise flows in the route of by AVRH-C Bypass capacitor.
  • AVCC / AVSS
    • AVCC-C Bypass capacitor “0.1 μF” is connected between AVCC and AVSS lines.
    • AVCC-R Register “10Ω ” is populated on AVCC line. This is to make high frequency noise flows in the route of by AVCC-C Bypass capacitor.

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From Layout observation, AVRH-R, AVRH-C, AVCC-R and AVCC-C should be populated close to each pin without any vias to avoid redundant line length between the pin and register/capacitor:

  • AVRH pin to AVRH-R
  • AVRH pin to AVRH-C
  • AVRL pin to AVRH-C
  • AVSS pin to AVCC-C
  • AVCC pin to AVCC-C
  • AVCC

The line between the AVRL pin to AVRH-C should be separated from the line between AVSS pin and AVSS-C to avoid common impedance.

1.png

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