LTC1458LCSW datasheet(9/12 Pages) LINER

9 / 12 page

LTC1458/LTC1458L

APPLICATIONS INFORMATION

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 VCC/2, corresponding to DAC B’s code

≤ 2,500 for VCC = 5V, since DAC C is being operated in × 2

mode for full rail-to-rail output swing.

The transfer characteristic is:

VOUTC = 2 • [DC • (2 • DB – DA) + DA] • REFOUT

where REFOUT = The Reference Output

DA = (DAC A Digital Code)/4096

This sets the offset.

DB = (DAC B Digital Code)/4096

This sets the full scale.

DC = (DAC C Digital Code)/4096

VCC

X1/X2 B

VOUT B

CLR

REFHI B

GND

REFLO B

REFLO A

REFHI A

REFOUT

VOUT A

X1/X2 A

VCC

X1/X2 C

VOUT C

CS/LD

DIN

REFHI C

GND

REFLO C

REFLO D

REFHI D

DOUT

CLK

VOUT D

X1/X2 D

LTC1458

LTC1458L

0.1

µF

VOUT

1458 F02

500

Ω

Figure 2

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