Datasheet
DAC8218
SBAS460A –MAY 2009–REVISED DECEMBER 2009
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INPUT DATA FORMAT
The USB/BTC pin defines the input data format and the Offset DAC format. When this pin is connected to
DGND, the Input DAC data and Offset DAC data are straight binary, as shown in Table 1 and Table 3. When this
pin is connected to IOV
DD
, the Input DAC data and Offset DAC data are in twos complement format, as shown in
Table 2 and Table 4.
Table 1. Bipolar Output vs Straight Binary Code Using Dual Power Supplies with Gain = 6
USB CODE NOMINAL OUTPUT DESCRIPTION
3FFFh +3 × V
REF
× (8191/8192) +Full-Scale – 1 LSB
••• ••• ••• ••• ••• •••
2001h +3 × V
REF
× (1/8192) +1 LSB
2000h 0 Zero
1FFFh –3 × V
REF
× (1/8192) –1 LSB
••• ••• ••• ••• ••• •••
0000h –3 × V
REF
× (8192/8192) –Full-Scale
Table 2. Bipolar Output vs Twos Complement Code Using Dual Power Supplies with Gain = 6
BTC CODE NOMINAL OUTPUT DESCRIPTION
1FFFh +3 × V
REF
× (8191/8192) +Full-Scale – 1 LSB
••• ••• ••• ••• ••• •••
0001h +3 × V
REF
× (1/8192) +1 LSB
0000h 0 Zero
3FFFh –3 × V
REF
× (1/8192) –1 LSB
••• ••• ••• ••• ••• •••
2000h –3 × V
REF
× (8192/8192) –Full-Scale
Table 3. Unipolar Output vs Straight Binary Code Using Single Power Supply with Gain = 6
USB CODE NOMINAL OUTPUT DESCRIPTION
3FFFh +6 × V
REF
× (16383/16384) +Full-Scale – 1 LSB
••• ••• ••• ••• ••• •••
2001h +6 × V
REF
× (8193/16384) Midscale + 1 LSB
2000h +6 × V
REF
× (8192/16384) Midscale
1FFFh +6 × V
REF
× (8191/16384) Midscale – 1 LSB
••• ••• ••• ••• ••• •••
0000h 0 0
Table 4. Unipolar Output vs Twos Complement Code Using Single Power Supply with Gain = 6
BTC CODE NOMINAL OUTPUT DESCRIPTION
1FFFh +6 × V
REF
× (16383/16384) +Full-Scale – 1 LSB
••• ••• ••• ••• ••• •••
0001h +6 × V
REF
× (8193/16384) Midscale + 1 LSB
0000h +6 × V
REF
× (8192/16384) Midscale
3FFFh +6 × V
REF
× (8191/16384) Midscale – 1 LSB
••• ••• ••• ••• ••• •••
2000h 0 0
The data written to the Gain Register are always in straight binary, data to the Zero Register are in twos
complement, and data to all other control registers are as specified in the definitions, regardless of the USB/BTC
pin status.
In reading operation, the read-back data are in the same format as written.
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