Datasheet

18
®
DAC7641
FIGURE 15. 4-to-20mA Digitally Controlled Current Source.
1000pF
2200pF
OPA2350
100Ω
1000pF
2200pF
80kΩ
20kΩ
+0.50v
100Ω
+2.5V
+V
V
REFL
V
REFL
Sense
V
REFH
V
REFH
Sense
V
CC
AGND
30 29 28 27 26 25
DAC7641
V
OUT
Sense
V
OUT
V
SS
24
23
22
I
OUT
V
PROGRAMMED
R
SENSE
125Ω
DIGITALLY-PROGRAMMABLE
CURRENT SOURCE
The DAC7641 offers a unique set of features that allows a
wide range of flexibility in designing applications circuits
such as programmable current sources. The DAC7641 offers
both a differential reference input as well as an open-loop
configuration around the output amplifier. The open-loop
configuration around the output amplifier allows transistor
to be placed within the loop to implement a digitally-
programmable, uni-directional current source. The availabil-
ity of a differential reference also allows programmability
for both the full-scale and zero-scale currents. The output
current is calculated as:
Figure 15 shows a DAC7641 in a 4mA to 20mA current
output configuration. The output current can be determined
by Equation 3:
At full-scale, the output current is 16mA plus the 4mA for
the zero current. At zero scale the output current is the offset
current of 4mA (0.5V/125Ω).
(2)
(3)
I
VHVL
R
N Value
VLR
OUT
REF REF
SENSE
REF SENSE
=


















+
()
–
•
,
/
65 536
I
V V N Value V
OUT
=
















+




25 05
125 65 536
05
125
.–.
•
,
.
ΩΩ