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參數(shù)資料
| 型號(hào)： | LTC2758BILX#PBF |
| 廠商： | Linear Technology |
| 文件頁(yè)數(shù)： | 11/24頁(yè) |
| 文件大?。?/td> | 0K |
| 描述： | IC DAC 18BIT SPI/SRL 48-LQFP |
| 標(biāo)準(zhǔn)包裝： | 250 |
| 系列： | SoftSpan™ |
| 設(shè)置時(shí)間： | 2.1µs |
| 位數(shù)： | 18 |
| 數(shù)據(jù)接口： | 串行，SPI? |
| 轉(zhuǎn)換器數(shù)目： | 2 |
| 電壓電源： | 單電源 |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 48-LQFP |
| 供應(yīng)商設(shè)備封裝： | 48-LQFP（7x7） |
| 包裝： | 管件 |
| 輸出數(shù)目和類型： | 2 電流，單極；4 電流，雙極 |
| 配用： | DC1684A-A-ND - BOARD DAC LTC2758 |
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LTC2758
19
2758fa
For more information www.linear.com/LTC2758
APPLICATIONS INFORMATION
Op amp offset contributes mostly to DAC output offset
and gain error, and has minimal effect on INL and DNL.
For example, consider the LTC2758 in unipolar 5V output
range. (Note that for this example, the LSB size is 19V.)
An op amp offset of 35V will cause 1.8LSB of output
offset, and 1.8LSB of gain error; but 0.4LSB of INL, and
just 0.1LSB of DNL.
While not directly addressed by the simple equations in
Tables 4 and 5, temperature effects can be handled just as
easily for unipolar and bipolar applications. First, consult
an op amp’s data sheet to find the worst-case VOS and IB
over temperature. Then, plug these numbers in the VOS
and IB equations from Table 5 and calculate the tempera-
ture-induced effects.
For applications where fast settling time is important, Ap-
plication Note 120,
1ppm Settling Time Measurement for
a Monolithic 18-Bit DAC, offers a thorough discussion of
18-bit DAC settling time and op amp selection.
Recommendations
For DC or low-frequency applications, the LTC1150 is the
simplest 18-bit accurate output amplifier. An auto-zero
amp, its exceptionally low offset (10V max) and offset
drift (0.01V/°C) make nulling unnecessary. For swings
above 8V, use an LT1010 buffer to boost the load current
capability. The settling of auto-zero amps is a special case;
seeApplicationNote120,
1ppmSettlingTimeMeasurement
for a Monolithic 18-Bit DAC, Appendix E, for details.
TheLT1012andLT1001aregoodintermediateoutput-amp
solutionsthatachievemoderatespeedandgoodaccuracy.
They are also excellent choices for the reference inverting
amplifier in fixed-reference applications.
For high speed applications, the LTC1468 settles in 2.1s.
Note that the 75V max offset will degrade the INL at the
DAC output by up to 0.9LSB. For high-speed applications
demanding higher precision, the amplifier offset can be
nulled with a digital potentiometer.
TheTypicalApplicationonthelastpageshowsacomposite
output amplifier that achieves fast settling (8s) and very
low offset (3V max) without offset nulling. This circuit
offershighopen-loopgain(1000V/mVmin),lowinputbias
current (0.15nA max), fast slew rate (25V/s min), and a
highgain-bandwidthproduct(30MHztyp).Thehighspeed
path consists of an LTC6240, which is an 18MHz ultralow
bias current amplifier, followed by an LT1360, a 50MHz
fast-slewing amplifier which provides additional gain and
the ability to swing to ±10V at the output. Compensation is
taken from the output of the LTC6240, allowing the use of
a much larger compensation capacitor than if taken after
the gain-of-five stage. An LTC2054 auto-zero amplifier
senses the voltage at IOUT1 and drives the non-inverting
input of the LTC6240 to eliminate the offset of the high
speed path. The 100:1 attenuator and input filter reduce
the low frequency noise in this stage while maintaining
low DC offset.
Precision Voltage Reference Considerations
Much in the same way selecting an operational amplifier
for use with the LTC2758 is critical to the performance of
the system, selecting a precision voltage reference also
requires due diligence. The output voltage of the LTC2758
is directly affected by the voltage reference; thus, any
voltage reference error will appear as a DAC output volt-
age error.
There are three primary error sources to consider
when selecting a precision voltage reference for 18-bit
applications:outputvoltageinitialtolerance,outputvoltage
temperature coefficient and output voltage noise.
Initial reference output voltage tolerance, if uncorrected,
generates a full-scale error term. Choosing a reference
with low output voltage initial tolerance, like the LT1236
(±0.05%),minimizesthegainerrorcausedbythereference;
however, a calibration sequence that corrects for system
zero- and full-scale error is always recommended.
Areference’soutputvoltagetemperaturecoefficientaffects
not only the full-scale error, but can also affect the circuit’s
INL and DNL performance. If a reference is chosen with
a loose output voltage temperature coefficient, then the
DAC output voltage along its transfer characteristic will
be very dependent on ambient conditions. Minimizing
the error due to reference temperature coefficient can be
achieved by choosing a precision reference with a low
output voltage temperature coefficient and/or tightly con-
trolling the ambient temperature of the circuit to minimize
temperature gradients.
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