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| 型号： | ADS7818P |
| 厂商： | Texas Instruments |
| 文件页数： | 20/21页 |
| 文件大小： | 0K |
| 描述： | IC 12-BIT 500KHZ A/D CONV 8-DIP |
| 产品培训模块： | Data Converter Basics |
| 标准包装： | 50 |
| 位数： | 12 |
| 采样率（每秒）： | 500k |
| 数据接口： | 串行 |
| 转换器数目： | 1 |
| 功率耗散（最大）： | 20mW |
| 电压电源： | 单电源 |
| 工作温度： | -40°C ~ 85°C |
| 安装类型： | 通孔 |
| 封装/外壳： | 8-DIP（0.300"，7.62mm） |
| 供应商设备封装： | 8-PDIP |
| 包装： | 管件 |
| 输入数目和类型： | 1 个差分，单极 |
| 产品目录页面： | 891 (CN2011-ZH PDF) |
| 配用： | 296-19913-ND - EVAL MOD FOR ADS7818 |
8
ADS7818
internal reference. This reference can be used to supply a
small amount of source current to an external load, but the
load should be static. Due to the internal 10k
resistor, a
dynamic load will cause variations in the reference voltage,
and will dramatically affect the conversion result. Note that
even a static load will reduce the internal reference voltage
seen at the buffer input. The amount of reduction depends on
the load and the actual value of the internal “10k
” resistor.
The value of this resistor can vary by
±30%.
The VREF pin should be bypassed with a 0.1F capacitor
placed as close as possible to the ADS7818 package. In
addition, a 2.2
F tantalum capacitor should be used in
parallel with the ceramic capacitor. Placement of this ca-
pacitor is not as critical.
EXTERNAL REFERENCE
The internal reference is connected to the VREF pin and to the
internal buffer via a 10k
series resistor. Thus, the reference
voltage can easily be overdriven by an external reference
voltage. The voltage range for the external voltage is 2.0V
to 2.55V, corresponding to an analog input range of 4.0V to
5.1V.
While the external reference will not source significant
current into the VREF pin, it does have to drive the series
10k
resistor that is terminated into the 2.5V internal
reference (the exact value of the resistor will vary up to
±30% from part to part). In addition, the V
REF pin should
still be bypassed to ground with at least a 0.1
F ceramic
capacitor (placed as close to the ADS7818 as possible). The
reference will have to be stable with this capacitive load.
Depending on the particular reference and A/D conversion
speed, additional bypass capacitance may be required, such
as the 2.2
F tantalum capacitor shown in Figure 1.
Reasons for choosing an external reference over the internal
reference vary, but there are two main reasons. One is to
achieve a given input range. For example, a 2.048V refer-
ence provides for a 0V to 4.095V input range—or 1mV per
LSB. The other is to provide greater stability over tempera-
ture. The internal reference is typically 20ppm/
°C which
translates into a full-scale drift of roughly 1 output code for
every 12
°C (this does not take into account other sources of
full-scale drift). If greater stability over temperature is needed,
then an external reference with lower temperature drift will
be required.
DIGITAL INTERFACE
Figure 2 shows the serial data timing and Figure 3 shows the
basic conversion timing for the ADS7818. The specific
timing numbers are listed in Table I. There are several
important items in Figure 3 which give the converter addi-
tional capabilities over typical 8-pin converters. First, the
transition from sample mode to hold mode is synchronous to
the falling edge of CONV and is not dependent on CLK.
Second, the CLK input is not required to be continuous
during the sample mode. After the conversion is complete,
the CLK may be kept LOW or HIGH.
FIGURE 2. Serial Data and Clock Timing.
SYMBOL
DESCRIPTION
MIN
TYP
MAX
UNITS
tACQ
Acquisition Time
350
ns
tCONV
Conversion Time
1.5
s
tCKP
Clock Period
125
5000
ns
tCKL
Clock LOW
50
ns
tCKH
Clock HIGH
50
ns
tCKDH
Clock Falling to Current Data
5
15
ns
Bit No Longer Valid
tCKDS
Clock Falling to Next Data Valid
30
50
ns
tCVL
CONV LOW
40
ns
tCVH
CONV HIGH
40
ns
tCKCH
CONV Hold after Clock Falls(1)
10
ns
tCKCS
CONV Setup to Clock Falling(1)
10
ns
tCKDE
Clock Falling to DATA Enabled
20
50
ns
tCKDD
Clock Falling to DATA
70
100
ns
High Impedance
tCKSP
Clock Falling to Sample Mode
5
ns
tCKPD
Clock Falling to Power-down Mode
50
ns
tCVHD
CONV Falling to Hold Mode
5
ns
(Aperture Delay)
tCVSP
CONV Rising to Sample Mode
5
ns
tCVPU
CONV Rising to Full Power-up
50
ns
tCVDD
CONV Changing State to DATA
70
100
ns
High Impedance
tCVPD
CONV Changing State to
50
ns
Power-down Mode
tDRP
CONV Falling to Start of CLK
5
s
(for hold droop < 0.1 LSB)
Note: (1) This timing is not required under some situations. See text for more information.
TABLE I. Timing Specifications (TA = –40°C to +85°C,
CLOAD = 30pF).
The asynchronous nature of CONV to CLK raises some
interesting possibilities, but also some design consider-
ations. Figure 3 shows that CONV has timing restraints in
relation to CLK (tCKCH and tCKCS). However, if these times
are violated (which could happen if CONV is completely
asynchronous to CLK), the converter will perform a conver-
sion correctly, but the exact timing of the conversion is
indeterminate. Since the setup and hold time between CONV
and CLK has been violated in this example, the start of
conversion could vary by one clock cycle. (Note that the
start of conversion can be detected by using a pull-up
resistor on DATA. When DATA drops out of high-imped-
ance and goes LOW, the conversion has started and that
clock cycle is this first of the conversion.)
In addition if CONV is completely asynchronous to CLK
and CLK is continuous, then there is possibility that CLK
will transition just prior to CONV going LOW. If this occurs
DATA
CLK
t
CKH
t
CKP
t
CKDH
t
CKDS
t
CKL
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相关代理商/技术参数 |
参数描述 |
|---|---|
| ADS7818P | 制造商:BURR-BROWN 功能描述:IC 12BIT ADC 7818 DIP8 制造商:Texas Instruments 功能描述:IC 12BIT ADC 500KHZ DIP8 制造商:Texas Instruments 功能描述:IC, 12BIT ADC, 500KHZ, DIP8 制造商:Texas Instruments 功能描述:IC, 12BIT ADC, 500KHZ, DIP8; Resolution (Bits):12bit; Sampling Rate:500kSPS; Supply Voltage Type:Single; Supply Voltage Min:4.75V; Supply Voltage Max:5.25V; Supply Current:2.2mA; Digital IC Case Style:DIP; No. of Pins:8; Input ;RoHS Compliant: Yes |
| ADS7818PB | 功能描述:模数转换器 - ADC 12-Bit High Speed Low Power Sampling RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| ADS7818PB | 制造商:Texas Instruments 功能描述:IC 12BIT ADC 500KHZ PDIP8 7818 |
| ADS7818PBG4 | 功能描述:模数转换器 - ADC 12-Bit High Speed Low Power Sampling RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
| ADS7818PG4 | 功能描述:模数转换器 - ADC 12-Bit High Speed Low Power Sampling RoHS:否 制造商:Texas Instruments 通道数量:2 结构:Sigma-Delta 转换速率:125 SPs to 8 KSPs 分辨率:24 bit 输入类型:Differential 信噪比:107 dB 接口类型:SPI 工作电源电压:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作温度:+ 85 C 安装风格:SMD/SMT 封装 / 箱体:VQFN-32 |
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