16.4 Notes on ADC
Several notes on ADC are listed below.
16.4.1 A/D Conversion Time
The user can select the appropriate conversion speed according to the frequency of the analog input signal. For
example, if Fosc=10MHz and a conversion speed of 270 clock cycles is selected, then the frequency of the
analog input should be no more than 37KHz to maintain the conversion accuracy. (Conversion time = 1/10MHz x
270 = 27us, so the conversion speed = 1/27us = 37KHz.)
16.4.2 I/O Pin Used with ADC Function
The analog input pins used with for the A/D converters also have its I/O port ‘s digital input and output function. In
order to give the best analog performance, a pin that is being used with the ADC should has its digital output and
input disabled. It is done by putting the port pin into the input-only mode as described in the Port Configurations
section.
16.4.3 Idle and Power-Down Mode
In Idle mode and Power-Down mode, the ADC does not function. If the A/D is turned on, it will consume a little
power. So, power consumption can be reduced by turning off the ADC hardware (ADCON=0) before entering Idle
mode and Power-Down mode.
16.4.4 Requirements on VDD Power Supply
As previously described, the Vref+ and Vref- are internally tied to VDD pin and ground, respectively, and the
operating voltage on VDD pin may be 2.7V~5.5V (in 5V application system) or 2.4V~3.6V (in 3.3V application
system), so the full-scale voltage, Vref+ – Vref- = VDD, is not fixed. However, the conversion formula is kept
unchanged. That is, the same Vin will get a different conversion result when the VDD voltage is changed, and
therefore the VDD must be kept fixed for an absolute conversion. The user should pay attention to it!
Since the VDD functions as the positive reference Vref+, the user should keep VDD as pure as possible in order
to achieve the best ADC performance.
MEGAWIN
MPC82G516A Data Sheet
84
MEGAWIN [ MEGAWIN TECHNOLOGY CO., LTD ]
