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參數資料
| 型號： | AD7992BRM-1 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | ADC |
| 英文描述： | 2-Channel, 12-Bit ADC with I2C Compatible Interface in 10-Lead MSOP |
| 中文描述： | 2-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, PDSO10 |
| 封裝： | MO-187-BA, MSOP-10 |
| 文件頁數： | 10/21頁 |
| 文件大小： | 266K |
| 代理商： | AD7992BRM-1 |
AD7992
–10–
REV. PrH
PRELIMINARY TECHNICAL DATA
CIRCUIT INFORMATION
The AD7992 is a fast, micro-power, 12-bit, single supply,
2 Channel A/D converter. The part can be operated from a
2.7 V to 5.5 V supply.
The AD7992 provides the user with a 2-channel multi-
plexer, an on-chip track/hold, A/D converter, an on-chip
oscillator, internal data registers and an I
2
C compatible
serial interface, all housed in a 10-lead MSOP package,
which offers the user considerable space saving advantages
over alternative solutions. An external reference is re-
quired by the AD7992, and this reference can be in the
range of 1.2 V to V
DD
.
The AD7992 will normally remain in a shutdown state
while not converting. When supplies are first applied the
part will come up in a power-down state. Power-up is
intitiated prior to a conversion and the device returns to
power-down upon completion of the conversion. Conver-
sions can be initiated on the AD7992 by either pulsing the
CONVST
signal, using an automatic cycling mode or
using a mode where wake-up and conversion occur during
the read function ( see modes of Operation section). On
completion of a conversion, the AD7992 will enter shut-
down mode again. This automatic shutdown feature allows
power saving between conversions. This means any read or
write operations across the serial interface can occur while
the device is in shutdown. The serial interface is I
2
C com-
patible.
ADC TRANSFER FUNCTION
The output coding of the AD7992 is straight binary. The
designed code transitions occur at successive integer LSB
values (i.e., 1LSB, 2LSBs, etc.). The LSB size for the
AD7992 is = REF
IN
/4096 . The ideal transfer characteris-
tic for the AD7992 is shown in Figure 4 below.
CONVERTER OPERATION
The AD7992 is a successive approximation analog-to -
digital converter based around a charge redistribution
DAC. Figures 2 and 3 show simplified schematics of the
ADC. Figure 2 shows the ADC during its acquisition
phase. SW2 is closed and SW1 is in position A, the com-
parator is held in a balanced condition and the sampling
capacitor acquires the signal on V
IN
.
When the ADC starts a conversion, see Figure 3, SW2
will open and SW1 will move to position B causing the
comparator to become unbalanced. The Control Logic
and the Charge Redistribution DAC are used to add and
subtract fixed amounts of charge from the sampling ca-
pacitor to bring the comparator back into a balanced con-
dition. When the comparator is rebalanced the conversion
is complete. The Control Logic generates the ADC out-
put code. Figure 4 shows the ADC transfer function.
Figure 2. ADC Acquisition Phase
Figure 3. ADC Conversion Phase
Figure 4. AD7992 Transfer Characteristic
TYPICAL CONNECTION DIAGRAM
Figure 5 shows the typical connection diagram for the
AD7992. In Figure 5 the Address Select pin, AS, is tied
to V
DD
, however AS can also be either tied to GND or
left floating, allowing the user to select up to three
AD7992 devices on the same serial bus. An external refer-
ence must be applied to the AD7992. This reference can
be in the range of 1.2 V to V
DD
. A precision reference
like the REF 19X family or the ADR421 can be used to
supply the Reference Voltage to the ADC.
SDA and SCL form the two-wire I
2
C/SMBus compatible
interface. External Pull up resistors should be added to
the SDA and SCL bus lines.
The AD7992-0 supports Standard and Fast I
2
C Interface
Modes. While the AD7992-1 supports Standard, Fast and
Highspeed I
2
C Interface Modes. Therefore if operating
the AD7992 in either Standard or Fast Mode, five
AD7992 (3 x AD7992-0 and 2 x AD7992-1 or 2 x
AD7992-0 and 3 x AD7992-1) parts can be connected to
the bus. When operating the AD7992 in Hs-Mode then up
to three AD7992-1 can be connected to the bus.
Wake-up from power-down prior to a conversion is ap-
proximately 1μs while conversion time is approximately
2μs. The AD7992 enters power-down mode again after
each conversion, this automatic powerdown feature will be
useful in applications where power consumption is of con-
cern.
CAPACITIVE
DAC
VIN
COMPARATOR
CONTROL
LOGIC
SW1
A
B
SW2
AGND
CAPACITIVE
DAC
VIN
COMPARATOR
CONTROL
LOGIC
SW1
A
B
SW2
AGND
000...000
A
ANALOG INPUT
0 V TO REFIN
111...111
111...110
000...001
000...010
111...000
011...111
AGND +1 LSB
+REFIN -1LSB
1LSB = REFIN/4096
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