- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄364640 > ADS7822C CMOS Dual 4-Input NOR Gate 14-TSSOP -55 to 125 PDF資料下載
參數(shù)資料
| 型號(hào)： | ADS7822C |
| 英文描述： | CMOS Dual 4-Input NOR Gate 14-TSSOP -55 to 125 |
| 中文描述： | 12位高速2.7微采樣模擬到數(shù)字轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 11/12頁(yè) |
| 文件大?。?/td> | 146K |
| 代理商： | ADS7822C |
11
ADS7822
This technique can be used to lower the power dissipation (or
to increase the conversion rate) in those applications where
an analog signal is being monitored until some condition
becomes true. For example, if the signal is outside a prede-
termined range, the full 12-bit conversion result may not be
needed. If so, the conversion can be terminated after the first
n-bits, where n might be as low as 3 or 4. This results in lower
power dissipation in both the converter and the rest of the
system, as they spend more time in the power down mode.
LAYOUT
For optimum performance, care should be taken with the
physical layout of the ADS7822 circuitry. This will be
particularly true if the reference voltage is low and/or the
conversion rate is high. At a 75kHz conversion rate, the
ADS7822 makes a bit decision every 830ns. That is, for each
subsequent bit decision, the digital output must be updated
with the results of the last bit decision, the capacitor array
appropriately switched and charged, and the input to the
comparator settled to a 12-bit level all within one clock cycle.
The basic SAR architecture is sensitive to spikes on the
power supply, reference, and ground connections that occur
just prior to latching the comparator output. Thus, during any
single conversion for an n-bit SAR converter, there are n
“windows” in which large external transient voltages can
easily affect the conversion result. Such spikes might origi-
nate from switching power supplies, digital logic, and high
power devices, to name a few. This particular source of error
can be very difficult to track down if the glitch is almost
synchronous to the converter’s DCLOCK signal—as the
phase difference between the two changes with time and
temperature, causing sporadic misoperation.
With this in mind, power to the ADS7822 should be clean
and well bypassed. A 0.1
μ
F ceramic bypass capacitor should
be placed as close to the ADS7822 package as possible. In
addition, a 1 to 10
μ
F capacitor and a 5
or
10
series
resistor may be used to lowpass filter a noisy supply.
The reference should be similarly bypassed with a 0.1
μ
F
capacitor. Again, a series resistor and large capacitor can be
used to lowpass filter the reference voltage. If the reference
voltage originates from an op amp, be careful that the op amp
can drive the bypass capacitor without oscillation (the series
resistor can help in this case). Keep in mind that while the
ADS7822 draws very little current from the reference on
average, there are still instantaneous current demands placed
on the external reference circuitry.
Also, keep in mind that the ADS7822 offers no inherent
rejection of noise or voltage variation in regards to the
reference input. This is of particular concern when the
reference input is tied to the power supply. Any noise and
ripple from the supply will appear directly in the digital
results. While high frequency noise can be filtered out as
described in the previous paragraph, voltage variation due to
the line frequency (50Hz or 60Hz), can be difficult to
remove.
The GND pin on the ADS7822 should be placed on a clean
ground point. In many cases, this will be the “analog”
ground. Avoid connecting the GND pin too close to the
grounding point for a microprocessor, microcontroller, or
digital signal processor. If needed, run a ground trace directly
from the converter to the power supply connection point. The
ideal layout will include an analog ground plane for the
converter and associated analog circuitry.
APPLICATION CIRCUITS
Figures 6 and 7 show some typical application circuits for
the ADS7822. Figure 6 uses an ADS7822 and a multiplexer
to provide for a flexible data acquisition circuit. A resistor
string provides for various voltages at the multiplexer input.
The selected voltage is buffered and driven into V
REF
. As
shown in Figure 6, the input range of the ADS7822 is
programmable to 100mV, 200mV, 300mV, or 400mV. The
100mV range would be useful for sensors such as the
thermocouple shown.
Figure 7 shows a basic data acquisition system. The ADS7822
input range is 0V to V
CC
, as the reference input is connected
directly to the power supply. The 5
resistor and 1
μ
F to
10
μ
F capacitor filter the microcontroller “noise” on the
supply, as well as any high-frequency noise from the supply
itself. The exact values should be picked such that the filter
provides adequate rejection of the noise.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| ADS7822E | CMOS Dual 4-Input NOR Gate 14-TSSOP -55 to 125 |
| ADS7822EB | 12-Bit, High-Speed, 2.7V microPower Sampling ANALOG-TO-DIGITAL CONVERTER |
| ADS7822EC | CMOS Dual 4-Input NOR Gate 14-CDIP -55 to 125 |
| ADS7823E250 | 12-Bit, Sampling A/D Converter with I2C?? INTERFACE |
| ADS7823 | CONN, M HDR 2X20 NO LATCH |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADS7822CIDGKRAN | 制造商:Texas Instruments 功能描述: |
| ADS7822E | 制造商:TI 制造商全稱:Texas Instruments 功能描述:12-Bit, High-Speed, 2.7V microPower Sampling ANALOG-TO-DIGITAL CONVERTER |
| ADS7822E/250 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit Hi-Speed 2.7V MicroPower Sampling RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32 |
| ADS7822E/250 | 制造商:Texas Instruments 功能描述:Analog/Digital Converter IC Number of Bi |
| ADS7822E/250G4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 12-Bit Hi-Speed 2.7V MicroPower Sampling RoHS:否 制造商:Texas Instruments 通道數(shù)量:2 結(jié)構(gòu):Sigma-Delta 轉(zhuǎn)換速率:125 SPs to 8 KSPs 分辨率:24 bit 輸入類型:Differential 信噪比:107 dB 接口類型:SPI 工作電源電壓:1.7 V to 3.6 V, 2.7 V to 5.25 V 最大工作溫度:+ 85 C 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:VQFN-32 |
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。