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参数资料
| 型号： | LTC2496IUHF#TRPBF |
| 厂商： | Linear Technology |
| 文件页数： | 17/32页 |
| 文件大小： | 0K |
| 描述： | IC ADC 16BIT DELTA SIG 38-QFN |
| 标准包装： | 2,500 |
| 位数： | 16 |
| 采样率（每秒）： | 6.9 |
| 数据接口： | MICROWIRE?，串行，SPI? |
| 转换器数目： | 1 |
| 功率耗散（最大）： | 800µW |
| 电压电源： | 单电源 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 38-WFQFN 裸露焊盘 |
| 供应商设备封装： | 38-QFN（5x7） |
| 包装： | 带卷 (TR) |
| 输入数目和类型： | 16 个单端，双极；8 个差分，双极 |
| 配用： | DC1011A-B-ND - BOARD DELTA SIGMA ADC LTC2496 |
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LTC2496
2496fb
applicaTions inForMaTion
When using the LTC2496’s internal oscillator, the input
capacitor array is switched at 123kHz. The effect of the
charge transfer depends on the circuitry driving the in-
put/reference pins. If the total external RC time constant
is less then 580ns the errors introduced by the sampling
process are negligible since complete settling occurs.
Typically,thereferenceinputsaredrivenfromalowimped-
ance source. In this case complete settling occurs even
with large external bypass capacitors. The inputs (CH0 to
CH15, COM), on the other hand, are typically driven from
larger source resistances. Source resistances up to 10k
mayinterfacedirectlytotheLTC2496andsettlecompletely;
however, the addition of external capacitors at the input
terminals in order to filter unwanted noise (anti-aliasing)
results in incomplete settling.
TheLTC2496offerstwomethodsofremovingtheseerrors.
The first is an automatic differential input current cancella-
tion (Easy Drive) and the second is the insertion of buffer
between the MUXOUT and ADCIN pins, thus isolating the
input switching from the source resistance.
Automatic Differential Input Current Cancellation
In applications where the sensor output impedance is
low (up to 10k with no external bypass capacitor or up
to 500
Ω with 0.001F bypass), complete settling of the
input occurs. In this case, no errors are introduced and
direct digitization is possible.
For many applications, the sensor output impedance
combined with external input bypass capacitors produces
RC time constants much greater than the 580ns required
for 1ppm accuracy. For example, a 10k bridge driving a
0.1F capacitor has a time constant an order of magnitude
greater than the required maximum.
The LTC2496 uses a proprietary switching algorithm
that forces the average differential input current to zero
independent of external settling errors. This allows direct
digitization of high impedance sensors without the need
of buffers.
The switching algorithm forces the average input current
on the positive input (IIN+) to be equal to the average input
current in the negative input (IIN–). Over the complete
conversion cycle, the average differential input current
(IIN+ – IIN–) is zero. While the differential input current is
zero, the common mode input current (IIN+ + IIN–)/2 is
proportional to the difference between the common mode
input voltage (VIN(CM)) and the common mode reference
voltage (VREF(CM)).
In applications where the input common mode voltage is
equal to the reference common mode voltage, as in the
case of a balanced bridge, both the differential and com-
mon mode input current are zero. The accuracy of the
converter is not compromised by settling errors.
In applications where the input common mode voltage is
constant but different from the reference common mode
voltage, the differential input current remains zero while
the common mode input current is proportional to the
difference between VIN(CM) and VREF(CM). For a reference
commonmodevoltageof2.5Vandaninputcommonmode
of 1.5V, the common mode input current is approximately
0.74A.Thiscommonmodeinputcurrentdoesnotdegrade
the accuracy if the source impedances tied to IN+ and
IN– are matched. Mismatches in source impedance lead
to a fixed offset error but do not effect the linearity or full
scale reading. A 1% mismatch in a 1k source resistance
leads to a 74V shift in offset voltage.
In applications where the common mode input voltage
varies as a function of the input signal level (single ended
type sensors), the common mode input current varies
proportionally with input voltage. For the case of balanced
inputimpedances,thecommonmodeinputcurrenteffects
are rejected by the large CMRR of the LTC2496, leading
to little degradation in accuracy. Mismatches in source
impedances lead to gain errors proportional to the dif-
ference between the common mode input and common
mode reference. 1% mismatches in 1k source resistances
lead to gain errors on the order of 15ppm. Based on the
stability of the internal sampling capacitors and the ac-
curacy of the internal oscillator, a one-time calibration will
remove this error.
In addition to the input sampling current, the input ESD
protection diodes have a temperature dependent leakage
current. This current, nominally 1nA (±10nA max) results
in a small offset shift. A 1k source resistance will create a
1V typical and a 10V maximum offset voltage.
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