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參數資料
| 型號： | AD7816-7818 |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 溫度/濕度傳感器 |
| 英文描述： | Single- and 4-Channel, 9 us, 10-Bit ADCs with On-Chip Temperature Sensor |
| 中文描述： | 與單核和4通道，9我們，10位ADC片上溫度傳感器 |
| 文件頁數： | 12/20頁 |
| 文件大?。?/td> | 279K |
| 代理商： | AD7816-7818 |
REV. C
–12–
AD7816/AD7817/AD7818
1.2V
REF
IN
SW1
2.5V
EXTERNAL
REFERENCE
DETECT
BUFFER
1.2V
26k
24k
Figure 9. On-Chip Reference
ADC TRANSFER FUNCTION
The output coding of the AD7816, AD7817, and AD7818 is
straight binary. The designed code transitions occur at succes-
sive integer LSB values (i.e., 1 LSB, 2 LSBs, etc.). The LSB
size is = 2.5 V/1024 = 2.44 mV. The ideal transfer characteristic
is shown in Figure 10 below.
ANALOG INPUT
0V
1LSB
+2.5V1LSB
1LSB=2.5/1024
2.44mV
A
111...111
111...110
111...000
011...111
000...010
000...001
000...000
Figure 10. ADC Transfer Function
TEMPERATURE MEASUREMENT
The on-chip temperature sensor can be accessed via multiplexer
Channel 0, i.e., by writing 0 0 0 to the channel address register.
The temperature is also the power on default selection. The
transfer characteristic of the temperature sensor is shown in
Figure 11 below. The result of the 10-bit conversion on Chan-
nel 0 can be converted to degrees centigrade by using the fol-
lowing equation.
T
AMB
= –103
°
C
+ (
ADC Code
/4)
–55°C
125°C
192Dec
912Dec
T
ADC CODE
Figure 11. Temperature Sensor Transfer Characteristic
A
IN
D1
C1
3pF
V
DD
D2
C2
4pF
V
BALANCE
CONVERT PHASE - SWITCH OPEN
TRACK PHASE - SWITCH CLOSED
R1
1k
Figure 7. Equivalent Analog Input Circuit
DC Acquisition Time
The ADC starts a new acquisition phase at the end of a conver-
sion and ends on the falling edge of the
CONVST
signal. At the
end of a conversion a settling time is associated with the sam-
pling circuit. This settling time lasts approximately 100 ns. The
analog signal on V
IN +
is also being acquired during this settling
time. Therefore, the minimum acquisition time needed is
approximately 100 ns.
Figure 8 shows the equivalent charging circuit for the sampling
capacitor when the ADC is in its acquisition phase. R2 repre-
sents the source impedance of a buffer amplifier or resistive
network, R1 is an internal multiplexer resistance and C1 is the
sampling capacitor.
V
IN
C1
3pF
R2
R1
1k
Figure 8. Equivalent Sampling Circuit
During the acquisition phase the sampling capacitor must be
charged to within a 1/2 LSB of its final value. The time it takes
to charge the sampling capacitor (T
CHARGE
) is given by the
following formula:
T
CHARGE
= 7.6
×
(
R
2 + 1
k
)
×
3
pF
For small values of source impedance, the settling time associ-
ated with the sampling circuit (100 ns) is, in effect, the acquisi-
tion time of the ADC. For example, with a source impedance (R2)
of 10
the charge time for the sampling capacitor is approxi-
mately 23 ns. The charge time becomes significant for source
impedances of 1 k
and greater.
AC Acquisition Time
In ac applications it is recommended to always buffer analog
input signals. The source impedance of the drive circuitry must
be kept as low as possible to minimize the acquisition time of
the ADC. Large values of source impedance will cause the THD
to degrade at high throughput rates.
ON-CHIP REFERENCE
The AD7816, AD7817, and AD7818 have an on-chip 1.2 V
band gap reference that is gained up to give an output of 2.5 V.
The on-chip reference is selected by connecting the REF
IN
pin
to analog ground. This causes SW1 (see Figure 9) to open and
the reference amplifier to power up during a conversion. There-
fore, the on-chip reference is not available externally. An external
2.5 V reference can be connected to the REF
IN
pin. This has the
effect of shutting down the on-chip reference circuitry and reduc-
ing I
DD
by about 0.25 mA.
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| AD7818AR | Single- and 4-Channel, 9 us, 10-Bit ADCs with On-Chip Temperature Sensor |
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD7816ACHIPS | 制造商:AD 制造商全稱:Analog Devices 功能描述:Single- and 4-Channel, 9 us, 10-Bit ADCs with On-Chip Temperature Sensor |
| AD7816AR | 制造商:Analog Devices 功能描述:Analog Temperature Sensors 8-Pin SOIC N 制造商:Rochester Electronics LLC 功能描述:TEMP SENSOR I.C. - Bulk 制造商:Analog Devices 功能描述:ADC TEMP SENSOR SMD 7816 SOIC8 |
| AD7816ARM | 制造商:Analog Devices 功能描述:Analog Temperature Sensors 8-Pin MSOP 制造商:Rochester Electronics LLC 功能描述:TEMPERATURE SENSOR: 10-BIT ADC, TEMPERATURE MONITORING ONLY - Bulk |
| AD7816ARM-REEL | 制造商:Analog Devices 功能描述:Analog Temperature Sensors 8-Pin MSOP T/R 制造商:Rochester Electronics LLC 功能描述:TEMPERATURE SENSOR: 10-BIT ADC, TEMPERATURE MONITORING ONLY - Tape and Reel |
| AD7816ARM-REEL7 | 制造商:Analog Devices 功能描述:Analog Temperature Sensors 8-Pin MSOP T/R |
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