Datasheet

9
LTC1458/LTC1458L
Using Two DACs to Digitally Program the Full Scale
and Offset of a Third
Figure 2 shows how to use one LTC1458 to make a 12-bit
DAC with a digitally programmable full scale and offset.
DAC A and DAC B are used to control the offset and full
scale of DAC C. DAC A is connected in a ×1 configuration
and controls the offset of DAC C by moving REFLO C above
ground. The minimum value to which this offset can be
programmed is 10mV. DAC B is connected in a × 2
configuration and controls the full scale of DAC C by
driving REFHI C. Note that the voltage at REFHI C must be
less than or equal to V
CC
/2, corresponding to DAC B’s code
≤ 2,500 for V
CC
= 5V, since DAC C is being operated in × 2
mode for full rail-to-rail output swing.
The transfer characteristic is:
V
OUTC
= 2 • [D
C
• (2 • D
B
– D
A
) + D
A
] • REFOUT
where REFOUT = The Reference Output
D
A
= (DAC A Digital Code)/4096
This sets the offset.
D
B
= (DAC B Digital Code)/4096
This sets the full scale.
D
C
= (DAC C Digital Code)/4096
V
CC
X1/X2 B
V
OUT B
CLR
REFHI B
GND
REFLO B
REFLO A
REFHI A
REFOUT
NC
V
OUT A
X1/X2 A
V
CC
X1/X2 C
V
OUT C
CS/LD
D
IN
REFHI C
GND
REFLO C
REFLO D
REFHI D
D
OUT
CLK
NC
V
OUT D
X1/X2 D
LTC1458
LTC1458L
0.1µF
V
OUT
5V
1458 F02
500Ω
Figure 2
APPLICATIO S I FOR ATIO
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