SLAS986D November 2014 – February 2018 AMC7836
In the AMC7836 mixed DAC range mode, a combination of DAC groups is set to a negative voltage output range (–5 to 0 V or –10 to 0 V) and a positive voltage output range (0 to 5 V or 0 to 10 V).
Because the maximum DAC output for each group cannot exceed the common AVCC voltage for the device (AVCC = AVCC_AB = AVCC_CD), a DAC group in the 0 to 10 V output range forces the AVCC voltage to a value greater or equal to 10 V. If all positive DAC groups are in the 0 to 5 V range the AVCC voltage can be set to a value as low as 5 V.
The minimum DAC output for each group cannot be lower than the voltage on the corresponding AVSS pins (AVEE, AVSSB, AVSSC and AVSSD). The AVSS pins are not required to be tied to the same potential and typically the negative voltage at each AVSS pin is dictated by the desired operating DAC negative output range. One exception is the AVEE pin which must be the lowest potential in the device. The implication of this requirement is that if either DAC group B, C or D is set to a negative output range, DAC group A must also be set to a negative range. The thermal pad should be either tied to the same potential as the AVEE pin or left disconnected. Table 7 lists the typical configurations for this mode.
|DVDD||DVDD must be equal to AVDD.||5 V|
|IOVDD||IOVDD must be equal to or less than DVDD.||1.8 V to 5 V|
|AVCC_AB, AVCC_CD||The AVCC_AB and AVCC_CD pins must be tied to the same potential (AVCC).
AVCC must be greater or equal to the maximum possible output voltage for any of the positive output range DACs.
|AVCC ≥ 5 V
AVCC ≥ 10 V
|AVEE||AVEE must be the lowest potential in the device.
AVEE must be less than or equal to the minimum possible output voltage for DAC group A.
|AVEE ≤ –5 V
AVEE ≤ –10 V
|AVSSB, AVSSC, AVSSD||AVSSn must be less than or equal than the minimum possible output voltage for DAC group n (n = B, C, D).||Negative Range||AVEE ≤ AVSSn ≤ –5 V
AVEE ≤ AVSSn ≤ –10 V
|Thermal Pad||AVEE or,
After power-on or a reset event the output range for each DAC group is set automatically by the voltage present in the corresponding AVSS pin. When the AVSS voltage of a DAC group is lower than the threshold value, AVSSTH, the output for that DAC group is automatically configured to the –10 to 0 V range. Conversely, if the AVSS voltage of the DAC group is higher than AVSSTH, the DAC-group output is automatically set to the 0 to 5 V range. The output for any of the DAC groups can be modified after initialization by setting the corresponding DAC range register (address 0x1E to 0x1F).
In addition to setting the default output range, the AVSS pins also set the clamp voltage for each DAC group. Because the clamp voltage is only dependent on the voltage in the AVSS pin, changes to the DAC range registers do not affect the clamp setting.
Although not a recommended operating condition, the device allows a DAC group to operate in a positive output range even if the clamp voltage is negative (AVSS connected to a negative supply voltage).