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參數(shù)資料
| 型號： | AD7854LARZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 10/28頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC ADC 12BIT PARALLEL LP 28-SOIC |
| 標(biāo)準(zhǔn)包裝： | 27 |
| 位數(shù)： | 12 |
| 采樣率（每秒）： | 100k |
| 數(shù)據(jù)接口： | 并聯(lián) |
| 轉(zhuǎn)換器數(shù)目： | 2 |
| 功率耗散（最大）： | 30mW |
| 電壓電源： | 模擬和數(shù)字 |
| 工作溫度： | -40°C ~ 85°C |
| 安裝類型： | 表面貼裝 |
| 封裝/外殼： | 28-SOIC（0.295"，7.50mm 寬） |
| 供應(yīng)商設(shè)備封裝： | 28-SOIC W |
| 包裝： | 管件 |
| 輸入數(shù)目和類型： | 1 個(gè)偽差分，單極；1 個(gè)偽差分，雙極 |
| 產(chǎn)品目錄頁面： | 779 (CN2011-ZH PDF) |
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AD7854/AD7854L
–18–
REV. B
Using The Internal (On-Chip) Reference
As in the case of an external reference the AD7854/AD7854L can
power up from one of two conditions, power-up after the sup-
plies are connected or power-up from a software power-down.
When using the on-chip reference and powering up when AVDD
and DVDD are first connected, it is recommended that the power-
up calibration mode be disabled as explained above. When using
the on-chip reference, the power-up time is effectively the time
it takes to charge up the external capacitor on the REFIN/
REFOUT pin. This time is given by the equation:
tUP = 9
× R × C
where R
≈ 150K and C = external capacitor.
The recommended value of the external capacitor is 100 nF;
this gives a power-up time of approximately 135 ms before a
calibration is initiated and normal operation should commence.
When CREF is fully charged, the power-up time from a software
power-down reduces to 5
s. This is because an internal switch
opens to provide a high impedance discharge path for the refer-
ence capacitor during power-down—see Figure 22. An added
advantage of the low charge leakage from the reference capacitor
during power-down is that even though the reference is being
powered down between conversions, the reference capacitor
holds the reference voltage to within 0.5 LSBs with throughput
rates of 100 samples/second and over with a full power-down
between conversions. A high input impedance op amp like the
AD707 should be used to buffer this reference capacitor if it is
being used externally. Note, if the AD7854/AD7854L is left in
its powered-down state for more than 100 ms, the charge on
CREF will start to leak away and the power-up time will increase.
If this longer power-up time is a problem, the user can use a
partial power-down for the last conversion so the reference
remains powered up.
SWITCH OPENS
DURING POWER-DOWN
TO OTHER CIRCUITRY
REFIN/OUT
EXTERNAL
CAPACITOR
ON-CHIP
REFERENCE
BUF
AD7854/
AD7854L
Figure 22. On-Chip Reference During Power-Down
POWER VS. THROUGHPUT RATE
The main advantage of a full power-down after a conversion is
that it significantly reduces the power consumption of the part
at lower throughput rates. When using this mode of operation,
the AD7854/AD7854L is only powered up for the duration of
the conversion. If the power-up time of the AD7854/AD7854L
is taken to be 5
s and it is assumed that the current during
power-up is 4.5 mA/1.5 mA typ, then power consumption as a
function of throughput can easily be calculated. The AD7854
has a conversion time of 4.6
s with a 4 MHz external clock,
and the AD7854L has a conversion time of 9
s with a 1.8 MHz
clock. This means the AD7854/AD7854L consumes 4.5 mA/
1.5 mA typ for 9.6
s/14 s in every conversion cycle if the parts
are powered down at the end of a conversion. The four graphs,
Figures 24, 25, 26 and 27, show the power consumption of the
AD7854 and AD7854L for VDD = 3 V as a function of through-
put. Table VII lists the power consumption for various throughput
rates.
Table VII. Power Consumption vs. Throughput
Power
Throughput Rate
AD7854
AD7854L
1 kSPS
130
W65 W
10 kSPS
1.3 mW
650
W
20 kSPS
2.6 mW
1.25 mW
50 kSPS
6.48 mW
3.2 mW
4MHz/1.8MHz
OSCILLATOR
AVDD DVDD
AIN(+)
AIN(–)
CREF1
CREF2
DB11
DB0
CONVST
AGND
DGND
CLKIN
REFIN/REFOUT
AD7854/
AD7854L
ANALOG
SUPPLY
+3V TO +5V
0.1 F
10 F
0.1 F
0.01 F
CONVERSION
START SIGNAL
0.1nF EXTERNAL REFERENCE
0.1 F ON-CHIP REFERENCE
0V TO 2.5V
INPUT
OPTIONAL
EXTERNAL
REFERENCE
CS
RD
WR
BUSY
AD780/
REF192
C/ P
HBEN
FULL POWER-DOWN
AFTER A CONVERSION
PMGT1 = 0
PMGT0 = 1
Figure 23. Typical Low Power Circuit
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| AD7854LARZ-REEL | 功能描述:IC ADC 12BIT PARALLEL LP 28SOIC RoHS:是 類別:集成電路 (IC) >> 數(shù)據(jù)采集 - 模數(shù)轉(zhuǎn)換器 系列:- 標(biāo)準(zhǔn)包裝:1,000 系列:- 位數(shù):16 采樣率（每秒）:45k 數(shù)據(jù)接口:串行 轉(zhuǎn)換器數(shù)目:2 功率耗散（最大）:315mW 電壓電源:模擬和數(shù)字 工作溫度:0°C ~ 70°C 安裝類型:表面貼裝 封裝/外殼:28-SOIC（0.295"，7.50mm 寬） 供應(yīng)商設(shè)備封裝:28-SOIC W 包裝:帶卷 (TR) 輸入數(shù)目和類型:2 個(gè)單端，單極 |
| AD7854LBR | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Analog-to-Digital Converter， 12-Bit |
| AD7854SQ | 制造商:Rochester Electronics LLC 功能描述:12-BIT SINGLE CH.PARALLEL ADC I.C. - Bulk |
| AD7856 | 制造商:AD 制造商全稱:Analog Devices 功能描述:5 V Single Supply, 8-Channel 14-Bit 285 kSPS Sampling ADC |
| AD7856AN | 制造商:Analog Devices 功能描述:ADC Single SAR 285ksps 14-bit Serial 24-Pin PDIP 制造商:Analog Devices 功能描述:IC 14BIT ADC 7856 DIP24 |
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