AD7992BRM-0(RevPrH) 查看數據表（PDF） - Analog Devices

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AD7992BRM-0
(Rev.:RevPrH)

2-Channel, 12-Bit ADC with I2C Compatible Interface in 10-Lead MSOP

Analog Devices 

AD7992

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 I2C 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 VDD.

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 I2C com-

patible.

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 VIN.

VIN

AGND

A

SW1

B

SW2

CAPACITIVE

DAC

COMPARATOR

CONTROL

LOGIC

Figure 2. ADC Acquisition Phase

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.

A

VIN

SW1

B

AGND

SW2

CAPACITIVE

DAC

COMPARATOR

CONTROL

LOGIC

Figure 3. ADC Conversion Phase

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 = REFIN/4096 . The ideal transfer characteris-

tic for the AD7992 is shown in Figure 4 below.

111...111

111...110

111...000

011...111

000...010

000...001

000...000

AGND +1 LSB

1LSB = REFIN/4096

+REFIN -1LSB

ANALOG INPUT

0 V TO REFIN

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 VDD, 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 VDD. 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 I2C/SMBus compatible

interface. External Pull up resistors should be added to

the SDA and SCL bus lines.

The AD7992-0 supports Standard and Fast I2C Interface

Modes. While the AD7992-1 supports Standard, Fast and

Highspeed I2C 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.

–10–

REV. PrH

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