How does the series resistor protect the ADC?
The series resistor after the Schottky diodes also helps limit the current into the ADC if the internal diodes turn on slightly. For extra protection, if the reference has little to no sink current capability, a Zener diode or clamp circuit could be used on the reference node to guarantee the reference voltage cannot be pulled too high.
How to protect ADC inputs from overvoltage?
A common issue that arises when designing an ADC circuit is how to protect the ADC inputs from overvoltage. The protection of ADC inputs has many scenarios and potential solutions. ADCs from all vendors have similar needs in this respect.
Can a strong driver circuit damage an ADC?
If the REF node is not driven by a strong driver circuit, then the voltage at the REF node (and input) will rise above the absolute maximum rated voltage and the ADC may be damaged if the voltage exceeds the breakdown voltage of devices on that process.
Why are ADC conversions inaccurate in a multi-ADC system?
In a simultaneous sampling multi-ADC system sharing the one reference, the conversions on the other ADCs will be inaccurate, as the system depends on a highly accurate reference voltage. Subsequent conversions may also be inaccurate if the recovery time from the fault condition is long.
What kind of diode is used for a 5 V reference?
In Figure 2, a 5.6 V Zener diode is used for a 5 V reference. An example is shown in Figure 4 of the effect on the reference input (5 V) of adding Schottky diodes to the ADC input when overdriving the ADC input with a sine wave. The Schottky diodes are connected to the ground and a 5 V system rail capable of sinking current.
When does overdrive of ADC inputs take place?
Overdrive of ADC inputs generally occurs when the rails of the driving amplifier are significantly greater than the max input range of the ADC—for example, if the amplifier runs from ±15 V and the ADC input is 0 V to 5 V.