DAC128S085CIMTX/NOPB National Semiconductor, DAC128S085CIMTX/NOPB Datasheet - Page 17

• Manufacturer Part Number: DAC128S085CIMTX/NOPB
• Description: IC DAC 12BIT 8CH RR OUT 16TSSOP
• Manufacturer: National Semiconductor
• Series: PowerWise®r

Specifications of DAC128S085CIMTX/NOPB

• Settling Time: 6µs
• Number Of Bits: 12
• Data Interface: Serial
• Number Of Converters: 8
• Voltage Supply Source: Single Supply
• Power Dissipation (max): 4.85mW
• Operating Temperature: -40°C ~ 105°C
• Mounting Type: Surface Mount
• Package / Case: 16-TSSOP
• For Use With: DAC128S085EB - BOARD EVALUATION FOR DAC128S085
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: DAC128S085CIMTX

2.2.1 LM4132
The LM4132, with its ±0.05% accuracy over temperature, is
a good choice as a reference source for the DAC128S085.
The 4.096V version is useful if a 0V to 4.095V output range
is desirable. Bypassing the LM4132 voltage input pin with a
4.7µF capacitor and the voltage output pin with a 4.7µF ca-
pacitor will improve stability and reduce output noise. The
LM4132 comes in a space-saving 5-pin SOT23.
2.2.2 LM4050
Available with accuracy of ±0.1%, the LM4050 shunt refer-
ence is also a good choice as a reference for the
DAC128S085. It is available in 4.096V and 5V versions and
comes in a space-saving 3-pin SOT23.
The minimum resistor value in the circuit of Figure 9 must be
chosen such that the maximum current through the LM4050
does not exceed its 15 mA rating. The conditions for maxi-
mum current include the input voltage at its maximum, the
LM4050 voltage at its minimum, and the DAC128S085 draw-
ing zero current. The maximum resistor value must allow the
LM4050 to draw more than its minimum current for regulation
plus the maximum DAC128S085 current in full operation. The
conditions for minimum current include the input voltage at its
minimum, the LM4050 voltage at its maximum, the resistor
value at its maximum due to tolerance, and the DAC128S085
draws its maximum current. These conditions can be sum-
marized as
and
FIGURE 8. The LM4132 as a power supply
FIGURE 9. The LM4050 as a power supply
R(min) = ( V
IN
(max) − V
Z
(min) ) /I
Z
(max)
30016914
30016913
17
where V
voltages ± the LM4050 output tolerance over temperature, I
(max) is the maximum allowable current through the LM4050,
I
proper
DAC128S085 supply current.
2.2.3 LP3985
The LP3985 is a low noise, ultra low dropout voltage regulator
with a ±3% accuracy over temperature. It is a good choice for
applications that do not require a precision reference for the
DAC128S085. It comes in 3.0V, 3.3V and 5V versions, among
others, and sports a low 30 µV noise specification at low fre-
quencies. Since low frequency noise is relatively difficult to
filter, this specification could be important for some applica-
tions. The LP3985 comes in a space-saving 5-pin SOT23 and
5-bump micro SMD packages.
An input capacitance of 1.0µF without any ESR requirement
is required at the LP3985 input, while a 1.0µF ceramic ca-
pacitor with an ESR requirement of 5mΩ to 500mΩ is required
at the output. Careful interpretation and understanding of the
capacitor specification is required to ensure correct device
operation.
2.2.4 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.
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 combi-
Z
(min) is the minimum current required by the LM4050 for
R(max) = ( V
Z
regulation,
FIGURE 10. Using the LP3985 regulator
FIGURE 11. Using the LP2980 regulator
(min) and V
IN
(min) − V
Z
and
(max) are the nominal LM4050 output
Z
(max) ) / ( (I
I
DAC
(max)
DAC
is
(max) + I
the
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maximum
30016915
Z
(min) )
30016916
Z