Hi Team,
Customer is going to use ADC CH0 and CH1 for differential input with full scale input range -Vref ~ Vref. I believe I should set bit 15 in ADC gain register for targeting operation. What about bit 14? Is it Don't care?
In addition, I'm a bit confused about full scale input voltage. When I set the FS range at -Vref ~ Vref, the voltage VDM = 2x (VDM/2) would be stored in ADC data register, and VDM should be between -2.5V and 2.5V. Is my understanding correct?
Good afternoon, apologies for the delay in getting back to you as I was looking into your questions.
1) With regards to the ADC gain register setting your understanding is correct in that bit 14 is don't care, but for a full scale range of -Vref to +Vref you must set bit 15 to 0 (i.e. bit 15 must be cleared). Please note that as per Table 23 in the datasheet (shown below) you also need to set bit 12 of ADC Channel Register 0 with all other bits set to 0 (if you only intend to use CH0 and CH1; else please refer to Table 24 for configuring CH2 and CH3).
2) For a FS range of -Vref ~ Vref, VDM can be between 0 and 2.5 V. It will not be negative as each of the differential input voltages V1 and V2 can range from 0 to 2.5V, and VDM is a measure of the difference between these voltages (i.e V1 - V2 if V1 > V2, or V2 - V1 if V1 < V2). The value VDM is used to determine the magnitude stored in bits 0 through 14 of the ADC data register while the MSB (bit 15) will be set to 1 to indicate a negative value (if V2 is greater than V1) or set to 0 to indicate a positive value (if V1 is greater than V2).
