UG-498
ADuCM320 Hardware Reference Manual
Rev. C | Page 38 of 196
IDAC Data Register
The IDAC output is controlled by an internal 11-bit and 5-bit DAC.
The 11-bit DAC (IDACxDAT[27:17]) controls the most significant bits. The 5-bit DAC (IDACxDAT[16:12]) controls the LSBs. The two
MSBs of the 5-bit DAC (IDACxDAT[16:15]) overlap the two LSBs of the 11-bit DAC (IDACxDAT[18:17]) as shown in Figure 10.
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IDACxDAT
14-BIT IDAC OUTPUT
11-BIT DAC
5-BIT DAC
Figure 10. 14-Bit IDAC Output
The 11-bit DAC and the 5-bit DAC are guaranteed monotonic as individual DACs. This combination makes it possible to reach 14-bit
resolution—up to 16,384 unique output values. However, monotonicity is only guaranteed for 11 bits (DNL < −1 LSB).
IDACs—Common Use Cases
Case 1—Setting the Output Current of IDAC1 to Quarter Scale
Set up IDAC1CON to 10xxxx00b:
o
IDAC1CON[7] = 1: enable writes to the IDAC1DAT register
o
IDAC1CON[0] = 0: power up IDAC1
o
IDAC1CON[5:2] as per Table 26: set up the filter bandwidth as required
o
IDAC1CON[1] = 0: disable the IDAC1 pull-down current source
o
IDAC1DAT[3] = 0: clear the IDAC1 sync bit to allow immediate updating of the IDAC
o
IDAC1CON[6] = 0: disable the overtemperature shutdown feature
Set up IDAC1DAT to give a current output of quarter scale:
o
If IDAC1 is used in an open loop system or in a set and forget type operation, set IDAC1DAT = 0x03FE0000
Set IDAC1DAT[27:17] = 0x1FF
Set IDAC1DAT[16:12] = 0x00
o
If IDAC1 is used in a closed loop system, set IDAC1DAT = 0x03FCF000
Set IDAC1DAT[27:17] = 0x1FE
Set IDAC1DAT[16:12] = [01111]b
Adjust the 5-bit IDAC (IDAC1DAT[16:12]) up or down accordingly to attain the correct setting.
Case 2—Turn On IDAC2 but to Set the Output to 0 mA with the Lowest Possible Offset
Before powering up the IDACs, ensure that the internal reference is fully powered on.
Set up the IDAC2CON register to 10xxxx00b:
o
IDAC2CON[7] = 1: enable writes to the IDAC2DAT register
o
IDAC2CON[0] = 0: power up IDAC2
o
IDAC2CON[5:2] as per Table 26: set up the filter bandwidth as required
o
IDAC2CON[1] = 0: enable the IDAC2 pull-down current sink
o
IDAC2CON[6] = 0: disable the overtemperature shutdown feature
Set up the IDAC2DAT register
o
IDAC2DAT[27:12] = 0x0000: set the IDAC to zero scale
If any or all the IDACs are not used, connect the pins as follows:
o
IREF: If no IDACs are used, connect a low cost 3.3 kΩ resistor to ground.
o
If no PVDD supply is available, connect PVDDx of all IDACs to AVDD_REG1 (Ball F10).
Make sure not to power up such IDACs to avoid loading AVDD_REG1 unnecessarily.
o
CDAMPx of any IDAC not used, leave unconnected.
o
IDACx of individual IDAC not used:
Power down IDACx using PD bit (IDACxCON = 1; it is already powered down after reset).
Set IDACxDAT = 0 (zero current; it is already 0 after reset).
Connect IDACx pin to PGND.
