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參數(shù)資料
| 型號： | ADS7815U |
| 英文描述： | 16-Bit 250kHz Sampling CMOS ANALOG-to-DIGITAL CONVERTER |
| 中文描述： | 16位至250kHz采樣CMOS模擬數(shù)字轉(zhuǎn)換器 |
| 文件頁數(shù)： | 7/8頁 |
| 文件大?。?/td> | 140K |
| 代理商： | ADS7815U |
ADS7815
7
to that listed in the Specifications Table. The range for the
external reference is 2.3V to 2.7V.
REF PIN
The REF pin itself should be bypassed with a 0.1
μ
F ceramic
capacitor in parallel with a 2.2
μ
F tantalum capacitor. While
both capacitors should be physically close to the ADS7815,
it is very important that the ceramic capacitor be placed as
close as possible.
The REF voltage should not be used to drive a large load or
any load which is dynamic. A large load will reduce the
reference voltage and the corresponding input range of the
converter. A dynamic load will modulate the reference
voltage and this modulation will be present in the converter’s
output data.
CAP PIN
The voltage on the CAP pin is the output of the reference
buffer. This pin should be bypassed with a 0.1
μ
F ceramic
capacitor in parallel with a 2.2
μ
F tantalum capacitor. While
both capacitors should be physically close to the ADS7815,
it is very important that the ceramic capacitor be placed as
close as possible.
The CAP pin connects to the internal reference buffer and
directly to the binary weighted capacitor array of the con-
verter. Thus, the signal at the CAP pin has high-frequency
glitches which occur at each bit decision. For this reason, the
CAP voltage should not be used to provide a reference
voltage for external circuitry.
LAYOUT
The layout of the ADS7815 and accompanying components
will be critical for optimum performance. Use of an analog
ground plane is essential. Use of +5V and –5V power planes
is not critical as long as the supplies are well bypassed, and
the traces connecting +5V and –5V to the power connector
are not too long or too thin.
The two +V
S
power pins of the ADS7815 must be tied
together. The voltage source for these pins should also
power the input buffer and the 74HC00 shown in Figure 1.
This supply should separate from the positive +5V supply
for the system’s digital logic
Three ground pins are present on the ADS7815: pin 2, pin 5,
and pin 14. These should all be tied to the analog ground
plane. The analog ground plane should extend underneath
all analog signal conditioning components and up to the
74HC574s (or equivalent components) shown in Figure 1.
The 74HC574s should not be located more than several
inches from the ADS7815.
The ground for the 74HC574s should be connected to the
digital ground. The analog ground plane should extend up to
the 74HC574s but should be kept at least 1/4" (6mm) distant
from the digital ground plane (if present). The analog and
digital grounds planes should not overlap at any point.
R/C and CS should remain static prior to that start of
conversion and during the later part of a conversion. To start
a conversion, R/C should be taken LOW at least 100ns
before CS is taken LOW. R/C and/or CS should be taken
HIGH during the early part of the conversion, preferably
within 200ns of the start of the conversion. If these times are
not observed, then there is risk that the transition of these
digital signals may affect the conversion result.
The three NAND gates shown in Figure 1 can be used to
generate R/C and CS signals from a single negative going
pulse.
BUSY
BUSY goes LOW when a conversion is started and remains
LOW throughout the conversion. Just prior to BUSY going
HIGH, the digital outputs become active with the conversion
result. Time t
11
, shown in Figure 2, should provide adequate
time for the ADS7815 to drive the digital outputs to a valid
logic state before BUSY rises. As shown in Figure 1 and 2,
the rising edge of BUSY can be used to latch the digital
result into an external component.
DIGITAL OUTPUT
The ADS7815’s digital output is in Binary Two’s Comple-
ment (BTC) format. Table III shows the relationship be-
tween the digital output word and analog input voltage under
ideal conditions.
REFERENCE
The ADS7815 can be operated with the internal 2.5V refer-
ence or an external reference. By applying an external
reference to the REF pin, the internal reference is bypassed.
The reference voltage at REF is buffered internally.
The voltage at the reference input sets the full-scale range of
the converter. With the internal 2.5V reference, the input
range is
±
2.5V. Thus, the input range of the converter’s
analog input is simply
±
V
REF
, where V
REF
is the voltage at
the reference input. Because of internal gain and offset error,
the input range will not be exactly
±
V
REF
. The full-scale
error of the converter with an external reference will typi-
cally be 0.25% or less. The bipolar zero error will be similar
ANALOG
INPUT
DESCRIPTION
BINARY CODE
HEX CODE
Full Scale Range
±
2.5V
76
μ
V
Least Significant
Bit (LSB)
+Full Scale
(2.5V – 1LSB)
2.499924V
0111 1111 1111 1111
7FFF
Midscale
0V
0000 0000 0000 0000
0000
One LSB below
Midscale
–76
μ
V
–2.5V
1111 1111 1111 1111
FFFF
–Full Scale
1000 0000 0000 0000
8000
DIGITAL OUTPUT
BINARY TWO’S COMPLEMENT
Table III. Ideal Input Voltages and Output Codes.
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| ADS7815U/1K | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 16-Bit 250kHz Sampling CMOS 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 |
| ADS7815U/1KE4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 16-Bit 250kHz Sampling CMOS 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 |
| ADS7815UE4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 16-Bit 250kHz Sampling CMOS 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 |
| ADS7815UG4 | 功能描述:模數(shù)轉(zhuǎn)換器 - ADC 16-Bit 250kHz Sampling CMOS 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 |
| ADS7816 | 制造商:BB 制造商全稱:BB 功能描述:12-Bit High Speed Micro Power Sampling ANALOG-TO-DIGITAL CONVERTER |
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