参数资料
型号: DC790A
厂商: Linear Technology
文件页数: 17/28页
文件大小: 0K
描述: BOARD DELTA SIGMA ADC LTC2439-1
软件下载: QuikEval System
设计资源: DC790A Design File
DC790A Schematic
标准包装: 1
系列: QuikEval™
ADC 的数量: 1
位数: 16
采样率(每秒): 6.8
数据接口: MICROWIRE?,串行,SPI?
工作温度: 0°C ~ 70°C
已用 IC / 零件: LTC2439-1
已供物品:
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LTC2439-1
24
24391fa
IN, the expected drift of the dynamic current, offset and
gain errors will be insignificant (about 1% of their respec-
tive values over the entire temperature and voltage range).
Even for the most stringent applications, a one-time
calibration operation may be sufficient.
In addition to the input sampling charge, the input ESD
protection diodes have a temperature dependent leakage
current. This current, nominally 1nA (
±10nA max), results
in a small offset shift. A 15k source resistance will create
a 0LSB typical and 1LSB maximum offset voltage.
Reference Current
In a similar fashion, the LTC2439-1 samples the differen-
tial reference pins REF+ and REFtransferring small amount
of charge to and from the external driving circuits thus
producing a dynamic reference current. This current does
not change the converter offset, but it may degrade the
gain and INL performance. The effect of this current can be
analyzed in the same two distinct situations.
For relatively small values of the external reference capaci-
tors (CREF < 0.01F), the voltage on the sampling capacitor
settles almost completely and relatively large values for
the source impedance result in only small errors. Such
values for CREF will deteriorate the converter offset and
gain performance without significant benefits of reference
filtering and the user is advised to avoid them.
Larger values of reference capacitors (CREF > 0.01F) may
be required as reference filters in certain configurations.
Such capacitors will average the reference sampling charge
and the external source resistance will see a quasi con-
stant reference differential impedance. When FO = LOW
(internal oscillator and 50Hz/60Hz notch), the typical
differential reference resistance is 1.4M
which will gen-
erate a gain error of approximately 1LSB full scale for each
40
of source resistance driving REF+ or REF. When FO
is driven by an external oscillator with a frequency fEOSC
(external conversion clock operation), the typical differen-
tial reference resistance is 0.20 1012/fEOSC and each
ohm of source resistance driving REF+ or REFwill result
in 1.54 10–7 fEOSCLSB gain error at full scale. The effect
of the source resistance on the two reference pins is
additive with respect to this gain error. The typical +FS and
–FS errors for various combinations of source resistance
seen by the REF+ and REFpins and external capacitance
CREF connected to these pins are shown in Figures 19, 20,
21 and 22.
In addition to this gain error, the converter INL perfor-
mance is degraded by the reference source impedance.
When FO = LOW (internal oscillator and 50Hz/60Hz notch),
every 1000
of source resistance driving REF+ or REF
translates into about 1LSB additional INL error. When FO
is driven by an external oscillator with a frequency fEOSC,
every 100
of source resistance driving REF+ or REF
translates into about 5.5 10–7 fEOSCLSB additional INL
error. Figure 23 shows the typical INL error due to the
source resistance driving the REF+ or REFpins when
large CREF values are used. The effect of the source
resistance on the two reference pins is additive with
respect to this INL error. In general, matching of source
RSOURCE ()
1
10
100
1k
10k
100k
+FS
ERROR
(LSB)
24361 F19
0
–3
–2
–1
VCC = 5V
REF+ = 5V
REF = GND
IN+ = 5V
IN = 2.5V
FO = GND
TA = 25°C
CREF = 0.01F
CREF = 0.001F
CREF = 100pF
CREF = 0pF
RSOURCE ()
1
10
100
1k
10k
100k
FS
ERROR
(LSB)
2412 F19
3
0
1
2
VCC = 5V
REF+ = 5V
REF = GND
IN+ = GND
IN = 2.5V
FO = GND
TA = 25°C
CREF = 0.01F
CREF = 0.001F
CREF = 100pF
CREF = 0pF
Figure 19. +FS Error vs RSOURCE at REF
+ or REF(Small CIN)
Figure 20. –FS Error vs RSOURCE at REF+ or REF(Small CIN)
APPLICATIO S I FOR ATIO
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