I'm using the controller MC9S12ZVL Family which has PGA feature used for an ADC Value interfaced to Pressure Sensor.
Following are the Register configurations done
PGAEN = 1;
PGAGAIN = 0x02; /* 40x*/
PGAOFFSET = 0x00; /*Disabled OFFSET*/
/* ==== Analog Mode Operation for HVI pin (IGN_FB). ==== */
PTAL_PTAENL = SET; /* 1 PL0 is connected to ADC */
PTAL_PTTEL = SET; /* Input buffer enabled when used with analog function */
PTAL_PTADIRL = CLEAR; /* Input voltage divider active on analog input to ADC channel */
PIRL_PIRL0 = 0x00; /* ratio selected 1:6 */
tPGA settling time given is 56us.
Vref of ADC is 5v.
I have 2 analog signals output from the Low Pass Filter Circuits . These 2 signals are then fed into the microcontroller MC9S12ZVLA as the PGA circuit inputs.
These two inputs are given to PGA with a Settling time of 56us in between.
Issue: The value getting as PGA output for the inputs given is getting skewed occasionally. I guess, the settling time given to select the Inputs is not sufficient. Please suggest on this.
I tried giving 200us as settling time and the Outputs were stable.
I want to know is Settling time the reason for this, because in the Datasheet the typical sufficient settling time for input selection is mentioned as around 10us .
So changing it to 200us is way more than what the spec specifies right?