Datasheet

DAC121C081
V
OUT
0.1 PF
+
10 PF
+
-
+5V
R
1
R
2
-5V
+5V
±5V
10 pF
SDA
SCL
LP2980
1 PF
Input
Voltage
ON /
OFF
V
IN
V
OUT
V
OUT
= 0V to 5V
DAC121C081/5
0.1 PF
SDA
SCL
V
REF
V
A
DAC121C081, DAC121C085
SNAS395D –DECEMBER 2007–REVISED MARCH 2013 www.ti.com
LP2980
The LP2980 is an ultra low dropout regulator with a 0.5% or 1.0% accuracy over temperature, depending upon
grade. It is available in 3.0V, 3.3V and 5V versions, among others.
Figure 30. Using the LP2980 regulator
Like any low dropout regulator, the LP2980 requires an output capacitor for loop stability. This output capacitor
must be at least 1.0µF over temperature, but values of 2.2µF or more will provide even better performance. The
ESR of this capacitor should be within the range specified in the LP2980 data sheet. Surface-mount solid
tantalum capacitors offer a good combination of small size and ESR. Ceramic capacitors are attractive due to
their small size but generally have ESR values that are too low for use with the LP2980. Aluminum electrolytic
capacitors are typically not a good choice due to their large size and have ESR values that may be too high at
low temperatures.
BIPOLAR OPERATION
The DAC121C081 is designed for single supply operation and thus has a unipolar output. However, a bipolar
output may be obtained with the circuit in Figure 31. This circuit will provide an output voltage range of ±5 Volts.
A rail-to-rail amplifier should be used if the amplifier supplies are limited to ±5V.
Figure 31. 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) (5)
where D is the input code in decimal form. With V
A
= 5V and R1 = R2,
V
O
= (10 x D / 4096) - 5V (6)
A list of rail-to-rail amplifiers suitable for this application are indicated in Table 2.
Table 2. Some Rail-to-Rail Amplifiers
AMP PKGS Typ V
OS
Typ I
SUPPLY
LMP7701 SOT-23 37 uV 0.79 mA
LMV841 SC70-5 50 uV 1 mA
LMC7111 SOT-23 0.9 mV 25 µA
LM7301 SO-8, SOT-23 0.03 mV 620 µA
LM8261 SOT-23 0.7 mV 1 mA
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