LTC1458 Linear Technology, LTC1458 Datasheet - Page 9

• Manufacturer Part Number: LTC1458
• Description: Quad 12-Bit Rail-to-Rail Micropower DACs
• Manufacturer: Linear Technology

APPLICATIONS
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
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
U
CC
/2, corresponding to DAC B’s code
V
INFORMATION
OUT
U
500
W
X1/X2 C
V
CS/LD
D
REFHI C
GND
REFLO C
REFLO D
REFHI D
D
CLK
NC
V
X1/X2 D
OUT C
IN
OUT
OUT D
U
LTC1458L
LTC1458
Figure 2
2
mode for full rail-to-rail output swing.
The transfer characteristic is:
where REFOUT = The Reference Output
D
D
D
REFLO B
REFLO A
REFHI B
REFHI A
REFOUT
X1/X2 B
X1/X2 A
V
V
A
B
C
2,500 for V
OUT B
OUT A
V
GND
CLR
= (DAC A Digital Code)/4096
= (DAC B Digital Code)/4096
= (DAC C Digital Code)/4096
V
V
NC
OUTC
CC
CC
This sets the offset.
This sets the full scale.
= 2 • [D
CC
= 5V, since DAC C is being operated in 2
C
• (2 • D
1458 F02
LTC1458/LTC1458L
B
– D
0.1 F
A
) + D
5V
A
] • REFOUT
9