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零件编号 | DAC124S085 | ||
描述 | 12-Bit Micro Power QUAD Digital-to-Analog Converter | ||
制造商 | National Semiconductor | ||
LOGO | |||
1 Page
January 2007
DAC124S085
12-Bit Micro Power QUAD Digital-to-Analog Converter with
Rail-to-Rail Output
General Description
The DAC124S085 is a full-featured, general purpose QUAD
12-bit voltage-output digital-to-analog converter (DAC) that
can operate from a single +2.7V to 5.5V supply and consumes
1.1 mW at 3V and 2.4 mW at 5V. The DAC124S085 is pack-
aged in 10-lead LLP and MSOP packages. The 10-lead LLP
package makes the DAC124S085 the smallest QUAD DAC
in its class. The on-chip output amplifier allows rail-to-rail out-
put swing and the three wire serial interface operates at clock
rates up to 40 MHz over the entire supply voltage range.
Competitive devices are limited to 25 MHz clock rates at sup-
ply voltages in the 2.7V to 3.6V range. The serial interface is
compatible with standard SPI™, QSPI, MICROWIRE and
DSP interfaces.
The reference for the DAC124S085 serves all four channels
and can vary in voltage between 1V and VA, providing the
widest possible output dynamic range. The DAC124S085 has
a 16-bit input shift register that controls the outputs to be up-
dated, the mode of operation, the powerdown condition, and
the binary input data. All four outputs can be updated simul-
taneously or individually depending on the setting of the two
mode of operation bits.
A power-on reset circuit ensures that the DAC output powers
up to zero volts and remains there until there is a valid write
to the device. A power-down feature reduces power con-
sumption to less than a microWatt with three different termi-
nation options.
The low power consumption and small packages of the
DAC124S085 make it an excellent choice for use in battery
operated equipment.
The DAC124S085 is one of a family of pin compatible DACs,
including the 8-bit DAC084S085 and the 10-bit DAC104S085.
The DAC124S085 operates over the extended industrial tem-
perature range of −40°C to +105°C.
Features
■ Guaranteed Monotonicity
■ Low Power Operation
■ Rail-to-Rail Voltage Output
■ Power-on Reset to 0V
■ Simultaneous Output Updating
■ Wide power supply range (+2.7V to +5.5V)
■ Industry's Smallest Package
■ Power Down Modes
Key Specifications
■ Resolution
■ INL
■ DNL
■ Settling Time
■ Zero Code Error
■ Full-Scale Error
■ Supply Power
■ — Normal
— Power Down
12 bits
±8 LSB (max)
+0.7 / −0.5 LSB (max)
8.5 µs (max)
+15 mV (max)
−0.75 %FS (max)
1.1 mW (3V) / 2.4 mW (5V) typ
0.3 µW (3V) / 0.8 µW (5V) typ
Applications
■ Battery-Powered Instruments
■ Digital Gain and Offset Adjustment
■ Programmable Voltage & Current Sources
■ Programmable Attenuators
Pin Configuration
20173201
SPI™ is a trademark of Motorola, Inc.
© 2007 National Semiconductor Corporation
201732
20173202
www.national.com
Transfer Characteristic
Timing Diagrams
FIGURE 1. Input / Output Transfer Characteristic
20173205
FIGURE 2. Serial Timing Diagram
20173206
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2.1.3 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
DAC124S085. 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.
2.2 BIPOLAR OPERATION
The DAC124S085 is designed for single supply operation and
thus has a unipolar output. However, a bipolar output may be
obtained with the circuit in Figure 9. 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.
20173215
FIGURE 7. Using the LP3985 regulator
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.
2.1.4 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.
FIGURE 9. Bipolar Operation
20173217
The output voltage of this circuit for any code is found to be
VO = (VA x (D / 4096) x ((R1 + R2) / R1) - VA x R2 / R1)
where D is the input code in decimal form. With VA = 5V and
R1 = R2,
VO = (10 x D / 4096) - 5V
A list of rail-to-rail amplifiers suitable for this application are
indicated in Table 2.
TABLE 2. Some Rail-to-Rail Amplifiers
AMP
LMC7111
PKGS
DIP-8
SOT23-5
Typ VOS Typ ISUPPLY
0.9 mV
25 µA
LM7301
SO-8
SOT23-5
0.03 mV
620 µA
LM8261
SOT23-5
0.7 mV
1 mA
20173216
FIGURE 8. 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 combi-
nation of small size and ESR. Ceramic capacitors are attrac-
tive 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 tem-
peratures.
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页数 | 20 页 | ||
下载 | [ DAC124S085.PDF 数据手册 ] |
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