DAC128S085EB/NOPB National Semiconductor, DAC128S085EB/NOPB Datasheet - Page 18

• Manufacturer Part Number: DAC128S085EB/NOPB
• Description: BOARD EVALUATION FOR DAC128S085
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of DAC128S085EB/NOPB

• Number Of Dac's: 8
• Number Of Bits: 12
• Outputs And Type: 8, Single Ended
• Data Interface: Serial
• Settling Time: 6µs
• Dac Type: Voltage
• Voltage Supply Source: Single
• Operating Temperature: -40°C ~ 105°C
• Utilized Ic / Part: DAC128S085
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: DAC128S085EB

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nation of small size and low ESR. Ceramic capacitors are
attractive due to their small size but generally have ESR val-
ues that are too low for use with the LP2980. Aluminum
electrolytic capacitors are typically not a good choice due to
their large size and high ESR values at low temperatures.
2.3 BIPOLAR OPERATION
The DAC128S085 is designed for single supply operation and
thus has a unipolar output. However, a bipolar output may be
achieved with the circuit in Figure 12. 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.
The output voltage of this circuit for any code is found to be
where D is the input code in decimal form. With V
R1 = R2,
A list of rail-to-rail amplifiers suitable for this application are
indicated in Table 5.
2.4 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 13, one of the channels of the DAC128S085 is con-
verted to a variable current source capable of sourcing up to
40mA.
V
O
LMC7111
LMP7701
LMV841
LM7301
LM8261
= (V
AMP
TABLE 5. Some Rail-to-Rail Amplifiers
A
x (D / 4096) x ((R1 + R2) / R1) - V
FIGURE 12. Bipolar Operation
V
O
SOT23-5
SOT23-5
SOT23-5
SOT23-5
SOT23-5
= (10 x D / 4096) - 5V
PKGS
Typ V
±37 µV
−17 µV
900 µV
700 µV
30 µV
OS
A
Typ I
x R2 / R1)
0.79 mA
1.11 mA
620 µA
25 µA
A
1 mA
= 5V and
SUPPLY
30016917
18
The output current of this circuit (I
to be
where D is the input code in decimal form and R
2.5 APPLICATION CIRCUITS
The following figures are examples of the DAC128S085 in
typical application circuits. These circuits are basic and will
generally require modification for specific circumstances.
2.5.1 Industrial Application
Figure 14 shows the DAC128S085 controlling several differ-
ent circuits in an industrial setting. Channel A is shown pro-
viding the reference voltage to the ADC121S625, one of
National Semiconductor's general purpose Analog-to-Digital
Converters (ADCs). The reference for the ADC121S625 may
be set to any voltage from 0.2V to 5.5V, providing the widest
dynamic range possible. Typically, the ADC121S625 will be
monitoring a sensor and would benefit from the ADC's refer-
ence voltage being adjustable. Channel B is providing the
drive or supply voltage for a sensor. By having the sensor
supply voltage adjustable, the output of the sensor can be
optimized to the input level of the ADC monitoring it. Channel
C is defined to adjust the offset or gain of an amplifier stage
in the system. Channel D is configured with an opamp to pro-
vide an adjustable current source. Being able to convert one
of the eight channels of the DAC128S085 to a current output
eliminates the need for a separate current output DAC to be
added to the circuit. Channel E, in conjunction with an opamp,
provides a bipolar output swing for devices requiring control
voltages that are centered around ground. Channel F and G
are used to set the upper and lower limits for a range detector.
Channel H is reserved for providing voltage control or acting
as a voltage setpoint.
I
FIGURE 13. Variable Current Source
O
= (V
REF
x (D / 4096) x (R
O
) for any DAC code is found
2
) / (R
1
x R
2
B
)
= R
A
30016958
+ R
B
.