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參數(shù)資料
| 型號： | LTC2435CGN#TRPBF |
| 廠商： | Linear Technology |
| 文件頁數(shù)： | 33/42頁 |
| 文件大小： | 0K |
| 描述： | IC ADC DIFF I/REF 20BIT 16-SSOP |
| 標(biāo)準(zhǔn)包裝： | 2,500 |
| 位數(shù)： | 20 |
| 采樣率（每秒）： | 15 |
| 數(shù)據(jù)接口： | MICROWIRE?，串行，SPI? |
| 轉(zhuǎn)換器數(shù)目： | 2 |
| 功率耗散（最大）： | 1mW |
| 電壓電源： | 單電源 |
| 工作溫度： | 0°C ~ 70°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 16-SSOP（0.154"，3.90mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 16-SSOP |
| 包裝： | 帶卷 (TR) |
| 輸入數(shù)目和類型： | 1 個(gè)差分，雙極 |
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LTC2435/LTC2435-1
39
24351fc
For more information www.linear.com/LTC2435
applicaTions inForMaTion
The listing in Figure 43 is a data collection program for the
LTC2435/LTC2435-1usingthePIC16F73microcontroller.
The microcontroller is configured to transfer data through
the SPI serial interface. Figure 42 shows the connection.
The LT1180A is a dual RS232 driver/receiver pair with
integral charge pump that generates RS232 voltage levels
from a single 5V supply.
The program begins by declaring variables and allocating
memory locations to store the 24-bit conversion result.
The main sequence starts with pulling CS LOW. It then
waits for SDO to go LOW to start reading data. Three
bytes are read to the MCU and the LTC2435/LTC2435-1
will automatically start a new conversion. CS is also raised
to HIGH to ensure that a new conversion is started. The
collected data are sent out through the serial port at 57600
baud. This can be captured with a terminal program and
analyzed with a spreadsheet using the HEX2DEC function.
Correlated Double Sampling with the
LTC2435/LTC2435-1
The Typical Application on the back page of this data
sheet shows the LTC2435/LTC2435-1 in a correlated
double sampling circuit that achieves a noise floor of
under 100nV. In this scheme, the polarity of the bridge is
alternatedeveryothersampleandtheresultistheaverage
of a pair of samples of opposite sign. This technique has
the benefit of canceling any fixed DC error components
in the bridge, amplifiers and the converter, as these will
alternate in polarity relative to the signal. Offset voltages
and currents, thermocouple voltages at junctions of dis-
similar metals and the lower frequency components of
1/f noise are virtually eliminated.
The LTC2435/LTC2435-1 have the virtue of being able to
digitize an input voltage that is outside the range defined by
the reference, thereby providing a simple means to imple-
ment a ratiometric example of correlated double sampling.
This circuit uses a bipolar amplifier (LT1219—U1 and
U2) that has neither the lowest noise nor the highest gain.
It does, however, have an output stage that can effec-
tively suppress the conversion spikes from the LTC2435/
LTC2435-1. The LT1219 is a C-Load stable amplifier
that, by design, needs at least 0.1F output capacitance to
remainstable.The0.1Fceramiccapacitorsattheoutputs
(C1 and C2) should be placed and routed to minimize lead
inductance or their effectiveness in preventing envelope
detection in the input stage will be reduced. Alternatively,
several smaller capacitors could be placed so that lead
inductance is further reduced. This is a consideration
because the frequency content of the conversion spikes
extendsto50MHzormore.Theoutputimpedanceofmost
op amps increases dramatically with frequency but the
effective output impedance of the LT1219 remains low,
determined by the ESR and inductance of the capacitors
above 10MHz. The conversion spikes that remain at the
output of other bipolar amplifiers pass through the feed-
backnetworkandoftenoverdrivetheinputoftheamplifier,
producingenvelopedetection.RFImayalsobepresenton
the signal lines from the bridge; C3 and C4 provide RFI
suppression at the signal input, as well as suppressing
transient voltages during bridge commutation.
The wideband noise density of the LT1219 is 33nV/√Hz,
seemingly much noisier than the lowest noise amplifiers.
However, in the region just below the 1/f corner that is
not well suppressed by the correlated double sampling,
the average noise density is similar to the noise density
of many low noise amplifiers. If the amplifier is rolled
off below about 1500Hz, the total noise bandwidth is
determined by the converter’s SINC4 filter at about 12Hz.
The use of correlated double sampling involves averaging
even numbers of samples; hence, in this situation, two
sampleswouldbeaveragedtogiveaninput-referrednoise
level of about 100nVRMS.
Level shift transistors Q4 and Q5 are included to allow
excitation voltages up to the maximum recommended
for the bridge. In the case shown, if a 10V supply is
used, the excitation voltage to the bridge is 8.5V and
the outputs of the bridge are above the supply rail of the
ADC. U1 and U2 are also used to produce a level shift to
bring the outputs within the input range of the converter.
This instrumentation amplifier topology does not require
well-matched resistors in order to produce good CMRR.
However, the use of R2 requires that R3 and R6 match
well, as the common mode gain is approximately –12dB.
If the bridge is composed of four equal 350Ω resistors,
the differential component associated with mismatch
of R3 and R6 is nearly constant with either polarity of
excitation and, as with offset, its contribution is canceled.
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| LTC2435IGN | 功能描述:IC CONV A/D 20BIT DIFF 16-SSOP RoHS:否 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 位數(shù):16 采樣率（每秒）:15 數(shù)據(jù)接口:MICROWIRE?，串行，SPI? 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:480µW 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:38-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:38-QFN（5x7） 包裝:帶卷 (TR) 輸入數(shù)目和類型:16 個(gè)單端，雙極；8 個(gè)差分，雙極 配用:DC1011A-C-ND - BOARD DELTA SIGMA ADC LTC2494 |
| LTC2435IGN#PBF | 功能描述:IC ADC DIFF I/REF 20BIT 16-SSOP RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:2,500 系列:- 位數(shù):16 采樣率（每秒）:15 數(shù)據(jù)接口:MICROWIRE?，串行，SPI? 轉(zhuǎn)換器數(shù)目:1 功率耗散（最大）:480µW 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:38-WFQFN 裸露焊盤 供應(yīng)商設(shè)備封裝:38-QFN（5x7） 包裝:帶卷 (TR) 輸入數(shù)目和類型:16 個(gè)單端，雙極；8 個(gè)差分，雙極 配用:DC1011A-C-ND - BOARD DELTA SIGMA ADC LTC2494 |
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