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参数资料
| 型号： | DC1485A |
| 厂商： | Linear Technology |
| 文件页数： | 9/20页 |
| 文件大小： | 0K |
| 描述： | BOARD DAC LTC2757 |
| 软件下载： | QuikEval System |
| 设计资源： | DC1485A Design Files DC1485A Schematic |
| 标准包装： | 1 |
| 系列： | QuikEval™, SoftSpan™ |
| DAC 的数量： | 1 |
| 位数： | 18 |
| 数据接口： | 并联 |
| 设置时间： | 2.1µs |
| DAC 型： | 电流 |
| 已供物品： | 板 |
| 已用 IC / 零件： | LTC2757 |
| 相关产品： | DC590B-ND - BOARD DEMO USB SERIAL CONTROLLER LTC2757BCLX#PBF-ND - IC DAC 18BIT PAR 48LQFP LTC2757ACLX#PBF-ND - IC DAC 18BIT PAR 48LQFP LTC2757BILX#PBF-ND - IC DAC 18BIT PAR 48LQFP LTC2757AILX#PBF-ND - IC DAC 18BIT PAR 48LQFP |
LTC2757
17
2757f
APPLICATIONS INFORMATION
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-ve
stage. An LTC2054 auto-zero amplier 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 lter 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 amplier
for use with the LTC2757 is critical to the performance of
the system, selecting a precision voltage reference also
requires due diligence. The output voltage of the LTC2757
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 appli-
cations: output voltage initial tolerance, output voltage
temperature coefcient 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%), minimizes the gain error caused by the reference;
however, a calibration sequence that corrects for system
zero- and full-scale error is always recommended.
A reference’s output voltage temperature coefcient affects
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 coefcient, then the
DAC output voltage along its transfer characteristic will
be very dependent on ambient conditions. Minimizing
the error due to reference temperature coefcient can be
achieved by choosing a precision reference with a low
output voltage temperature coefcient and/or tightly con-
trolling the ambient temperature of the circuit to minimize
temperature gradients.
As precision DAC applications move to 18-bit performance,
reference output voltage noise may contribute a dominant
share of the system’s noise oor. This in turn can degrade
system dynamic range and signal-to-noise ratio. Care
should be exercised in selecting a voltage reference with
as low an output noise voltage as practical for the system
resolution desired. Precision voltage references like the
LT1236 produce low output noise in the 0.1Hz to 10Hz
region, well below the 18-bit LSB level in 5V or 10V full-
scale systems. However, as the circuit bandwidths increase,
ltering the output of the reference may be required to
minimize output noise.
Table 6. Partial List of LTC Precision References Recommended
for Use with the LTC2757 with Relevant Specications
REFERENCE
INITIAL
TOLERANCE
TEMPERATURE
DRIFT
0.1Hz to 10Hz
NOISE
LT1019A-5,
LT1019A-10
±0.05%
Max
5ppm/°C
Max
12μVP-P
LT1236A-5,
LT1236A-10
±0.05%
Max
5ppm/°C
Max
3μVP-P
LT1460A-5,
LT1460A-10
±0.075%
Max
10ppm/°C
Max
20μVP-P
LT1790A-2.5
±0.05%
Max
10ppm/°C
Max
12μVP-P
LTC6655-2.5
LTC6655-5
±0.025%
Max
2ppm/°C
Max
0.62μVP-P
Grounding
As with any high-resolution converter, clean grounding is
important. A low-impedance analog ground plane is nec-
essary, as are star grounding techniques. Keep the board
layer used for star ground continuous to minimize ground
resistances; that is, use the star-ground concept without
using separate star traces. The IOUT2 pins are of particular
concern; INL will be degraded by the code-dependent
currents carried by the IOUT2F and IOUT2S pins if voltage
drops to ground are allowed to develop. The best strategy
here is to tie the pins to the star ground plane by multiple
vias located directly underneath the part. Alternatively, the
pins may be routed to the star ground point if necessary;
join them together at the part and route a single trace of
no more than 30 squares of 1oz copper.
In the rare case in which neither of these alternatives is
practicable, a force/sense amplier should be used as a
ground buffer (see the Typical Applications section). Note,
however, that the voltage offset of the ground buffer amp
directly contributes to the effects on accuracy specied in
Table 4 under ‘VOS1’. The combined effects of the offsets
can be calculated by substituting the total offset from IOUT1
to IOUT2S for VOS1 in the equations.
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