10.3 What To Do and What Not To Do
- Do partition the analog, digital, and power-supply circuitry into separate sections on the printed circuit board (PCB).
- Do use a single ground plane for analog and digital grounds.
- Do place the analog components close to the ADC pins using short, direct connections.
- Do keep the SCLK pin free of glitches and noise.
- Do verify that the analog input voltages are within the specified voltage range under all input conditions.
- Do tie unused analog input pins to GND.
- Do provide current limiting to the analog inputs in case overvoltage faults occur.
- Do use a low-dropout (LDO) regulator to reduce ripple voltage generated by switch-mode power supplies. This reduction is especially true for AVDD where the supply noise can affect performance.
- Do keep the input series resistance low to maximize THD performance.
- Do not cross analog and digital signals.
- Do not allow the analog power supply voltages (AVDD – AVSS) to exceed 3.6 V under any conditions, including during power-up and power-down when the negative charge pump is enabled.
- Do not allow the analog power supply voltages (AVDD – AVSS) to exceed 6 V under any conditions, including during power-up and power-down when the negative charge pump is disabled.
- Do not allow the digital supply voltage to exceed 3.9 V under any conditions, including during power-up and power-down.
Figure 104 and Figure 105 illustrate correct and incorrect ADC circuit connections.