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

mode for full rail-to-rail output swing.

The transfer characteristic is:

where REFOUT = The Reference Output

This sets the offset.

This sets the full scale.

X1/X2 B

CLR

REFHI B

GND

REFLO B

REFLO A

REFHI A

REFOUT

NC

X1/X2 A

X1/X2 C

CS/LD

REFHI C

GND

REFLO C

REFLO D

REFHI D

CLK

NC

X1/X2 D

LTC1458

LTC1458L

0.1

µF

5V

1458 F02

500

Ω

Figure 2