TLC7225C, TLC7225I

QUADRUPLE 8-BIT DIGITAL-TO-ANALOG CONVERTERS

SLAS109B – OCTOBER 1996 – REVISED FEBRUARY 2001

15

POST OFFICE BOX 655303

APPLICATION INFORMATION

bipolar-output operation using external amplifier

Each of the DACs of the TLC7225 can also be individually configured to provide bipolar output operation using

an external amplifier and two resistors per channel. Figure 11 shows a circuit used to implement offset binary

coding (bipolar operation) with DAC A of the TLC7225. In this case (see equation 1):

V

O +

1

) R2

R1

D

A

V

ref *

R2

R1

V

ref

with R1

+ R2

V

O +

2D

A *

1 V

ref

where D

A

is a fractional representation of the digital word in latch A.

(1)

Mismatch between R1 and R2 causes gain and offset errors. Therefore, these resistors must match and track

over temperature. The TLC7225 can be operated with a single supply or from positive and negative supplies.

15 V

_

+

DAC A

TLC7225

2

5

R2†

R1†

VO

REFA

† R1 = R2 = 10 k

Ω ±0.1%

_

+

– 15 V

Figure 11. Bipolar-Output Circuit

multiplying DAC using ac input to the REF terminals

The TLC7225 can be used as a multiplying DAC when the reference signal is maintained between 2 V and

should be used so that the input signal is not loaded by the resistor ladder. Figure 12 shows the general

schematic.

_

+

_

+

DAC

AGND

DGND

67

1/4 TLC7225

5, 4, 21, 20

15 V

REF (A, B, C, D)

OP - 15

15 V

R1

R2

AC Reference

Input Signal

VO

15 V

VDD

Figure 12. AC Signal-Input Scheme