Datasheet

DIN
SCLK
SYNC
V
OUT
0.1 PF
+
10 PF
+
-
R
1
R
2
+5V
R
3
(= R
1
)
R
A
R
B
Load
I
O
LMV710
V
REF
DAC128S085
DAC128S085
DIN
SCLK
SYNC
V
OUT
0.1 PF
+
10 PF
+
-
+5V
R
1
R
2
-5V
+5V
±5V
10 pF
V
A
/ V
REF1,2
DAC128S085
www.ti.com SNAS407F –AUGUST 2007–REVISED MARCH 2013
Figure 36. Bipolar Operation
The output voltage of this circuit for any code is found to be
V
O
= (V
A
x (D / 4096) x ((R1 + R2) / R1) - V
A
x R2 / R1) (6)
where D is the input code in decimal form. With V
A
= 5V and R1 = R2,
V
O
= (10 x D / 4096) - 5V (7)
A list of rail-to-rail amplifiers suitable for this application are indicated in Table 5.
Table 5. Some Rail-to-Rail Amplifiers
AMP PKGS Typ V
OS
Typ I
SUPPLY
LMP7701 SOT-23-5 ±37 µV 0.79 mA
LMV841 SOT-23-5 −17 µV 1.11 mA
LMC7111 SOT-23-5 900 µV 25 µA
LM7301 SOT-23-5 30 µV 620 µA
LM8261 SOT-23-5 700 µV 1 mA
VARIABLE CURRENT SOURCE OUTPUT
The DAC128S085 is a voltage output DAC but can be easily converted to a current output with the addition of an
opamp. In Figure 37, one of the channels of the DAC128S085 is converted to a variable current source capable
of sourcing up to 40mA.
Figure 37. Variable Current Source
The output current of this circuit (I
O
) for any DAC code is found to be
I
O
= (V
REF
x (D / 4096) x (R
2
) / (R
1
x R
B
) (8)
where D is the input code in decimal form and R
2
= R
A
+ R
B
.
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