DAC7632

14

SBAS234

www.ti.com

FIGURE 5. Dual Supply Configuration-Buffered References, used for Dual-Supply Performance.

V

V

V

V

V

V

V

V

32

31

30

29

28

27

26

25

DAC7632

1000pF

V

OUT

V

OUT

100

Ω

100

Ω

+2.5V

+V

–2.5V

–V

–V

+V

OPA2234

2200pF

1000pF

2200pF

V

V

V

V

V

V

V

V

32

31

30

29

28

27

26

25

DAC7632

R

W2

R

W1

+2.5V

+V

V

OUT

R

W1

R

W2

V

OUT

FIGURE 4. Analog Output Closed-Loop Configuration

ANALOG OUTPUTS

can swing to within 2.25V of the supply rails over the –40

°C

to +85

°C temperature range. When V

output can swing to ground. Care must also be taken when

output cannot swing below ground, the output voltage may

the negative limit of –2mV, the first specified output starts at

Due to the high accuracy of these DACs, system design

problems such as grounding and contact resistance become

very important. A 16-bit converter with a 2.5V full-scale range

has a 1LSB value of 38

µV. With a load current of 1mA, series

wiring and connector resistance of only 40m

Ω (R

cause a voltage drop of 40

µV, as shown in Figure 4. To

understand what this means in terms of a system layout, the

resistivity of a typical 1 ounce copper-clad printed circuit

board is 1/2m

Ω per square. For a 1mA load, a 10 milli-inch

wide printed circuit conductor 600 milli-inches long will result

in a voltage drop of 30

µV.

The DAC7632 offers a force and sense output configuration

for the high open-loop gain output amplifier. This feature

allows the loop around the output amplifier to be closed at the

load, as shown in Figure 4, thus ensuring an accurate output

voltage.

REFERENCE INPUTS

(essentially, the offset of the output op amp). The maximum

connected to ground or must be in the range of –4.75V to

the bias values may be in error and proper operation of the

device may be affected.

on the DAC output voltages, and can vary from a few

microamps to approximately 0.5mA. The reference input

appears as a varying load to the reference supply. If the

reference applied can sink or source the required current, a

reference buffer is not required. The DAC7632 features

reference drive and sense connections such that the internal

errors caused by the changing reference current and the

circuit impedances can be minimized. Figures 5 through 13

show different reference configurations and the effect on the

integral linearity and differential linearity, for each case.