参数资料
型号: LTC1408IUH-12#PBF
厂商: Linear Technology
文件页数: 6/20页
文件大小: 0K
描述: IC ADC 12BIT 600KSPS 32-QFN
标准包装: 73
位数: 12
采样率(每秒): 600k
数据接口: 串行
转换器数目: 1
功率耗散(最大): 15mW
电压电源: 模拟和数字
工作温度: -40°C ~ 85°C
安装类型: 表面贴装
封装/外壳: 32-WFQFN 裸露焊盘
供应商设备封装: 32-QFN 裸露焊盘(5x5)
包装: 管件
输入数目和类型: 12 个单端,单极;12 个单端,双极;6 个差分,单极;6 个差分,双极
产品目录页面: 1346 (CN2011-ZH PDF)
配用: DC887A-ND - BOARD SAR ADC LTC1408
14
LTC1408-12
140812f
APPLICATIO S I FOR ATIO
WU
UU
INPUT FILTERING AND SOURCE IMPEDANCE
The noise and the distortion of the input amplifier and
other circuitry must be considered since they will add to
the LTC1408-12 noise and distortion. The small-signal
bandwidth of the sample-and-hold circuit is 50MHz. Any
noise or distortion products that are present at the analog
inputs will be summed over this entire bandwidth. Noisy
input circuitry should be filtered prior to the analog inputs
to minimize noise. A simple 1-pole RC filter is sufficient for
many applications. For example, Figure 1 shows a 47pF
capacitor from CHO+ to ground and a 51
source resistor
to limit the net input bandwidth to 30MHz. The 47pF ca-
pacitor also acts as a charge reservoir for the input sample-
and-hold and isolates the ADC input from sampling-glitch
sensitive circuitry. High quality capacitors and resistors
should be used since these components can add distor-
tion. NPO and silvermica type dielectric capacitors have
excellent linearity. Carbon surface mount resistors can
generate distortion from self heating and from damage
that may occur during soldering. Metal film surface mount
resistors are much less susceptible to both problems.
When high amplitude unwanted signals are close in
frequency to the desired signal frequency a multiple pole
filter is required.
High external source resistance, combined with 13pF of
input capacitance, will reduce the rated 50MHz input band-
width and increase acquisition time beyond 39ns.
INPUT RANGE
The analog inputs of the LTC1408-12 may be driven fully
differentially with a single supply. Either input may swing
up to VCC, provided the differential swing is no greater than
2.5V with BIP (Pin 29) Low, or
±1.25V with (BIP Pin 29)
High. The 0V to 2.5V range is also ideally suited for single-
ended input use with single supply applications. The
common mode range of the inputs extend from ground to
the supply voltage VCC. If the difference between the CH+
and CHat any input pair exceeds 2.5V (unipolar) or 1.25V
(bipolar), the output code will stay fixed at positive full-
scale, and if this difference goes below 0V (unipolar) or –
1.25V (bipolar), the output code will stay fixed at negative
full-scale.
INTERNAL REFERENCE
The LTC1408-12 has an on-chip, temperature compen-
sated, bandgap reference that is factory trimmed to 2.5V
to obtain a precise 2.5V input span. The reference ampli-
fier output VREF, (Pin 23) must be bypassed with a capaci-
tor to ground. The reference amplifier is stable with capaci-
tors of 1
F or greater. For the best noise performance, a
10
F ceramic or a 10F tantalum in parallel with a 0.1F
ceramic is recommended. The VREF pin can be overdriven
with an external reference as shown in Figure 2. The volt-
age of the external reference must be higher than the 2.5V
of the open-drain P-channel output of the internal refer-
ence. The recommended range for an external reference
is 2.55V to VDD. An external reference at 2.55V will see a
DC quiescent load of 0.75mA and as much as 3mA
during conversion.
Figure 1. RC Input Filter
LTC1408-12
CH0+
CH0
VREF
GND
1408 F01
1
2
11
3
10
F
47pF*
51
*
CH1+
CH1
4
5
47pF*
*TIGHT TOLERANCE REQUIRED TO AVOID
APERTURE SKEW DEGRADATION
51
*
ANALOG
INPUT
ANALOG
INPUT
Figure 2. Overdriving VREF Pin with an External Reference
LTC2351-12
VREF
GND
1408 F02
23
22
10
F
LT1790-3
3.5V to 18V
3V
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