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AD7992

Rev. 0 | Page 14 of 28

TYPICAL CONNECTION DIAGRAM

Figure 21 shows the typical connection diagram for the

AD7992. In Figure 21, the address select pin (AS) is tied to VDD;

however AS can also be tied to AGND or left floating, allowing

the user to select up to five AD7992 devices on the same serial

bus. An external reference 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, ADR03, or ADR381 can be

used to supply the reference voltage to the ADC. The AD7992

can be configured to be a single-channel device with the

reference voltage applied to the VIN2/REFIN pin. The AD7992

can also be configured as a dual-channel device where the

reference voltage is taken from the supply voltage VDD, and the

VIN2/REFIN takes on its analog input function,VIN2.

SDA and SCL form the 2-wire I2C/SMBus-compatible interface.

External pull-up resisters are required for both SDA and SCL

lines.

The AD7992-0 supports standard and fast I2C interface modes.

The AD7992-1 supports standard, fast, and high speed I2C

interface modes. Therefore, if operating the AD7992 in either

standard or fast mode, up to five AD7992 devices can be

connected to the bus (3 × AD7992-0 and 2 × AD7992-1 or

3 × AD7992-1 and 2 × AD7992-0). In high speed mode, up to

three AD7992-1 devices can be connected to the bus.

Wake up from power-down prior to a conversion is approx-

imately 1 µs, and conversion time is approximately 2 µs. The

AD7992 enters shutdown mode again after each conversion,

which is useful in applications where power consumption is a

concern.

ANALOG INPUT

Figure 20 shows an equivalent circuit of the AD7992 analog

input structure. The two diodes, D1 and D2, provide ESD

protection for the analog inputs. Care must be taken to ensure

that the analog input signal does not exceed the supply rails

by more than 300 mV. This causes these diodes to become

forward-biased and start conducting current into the substrate.

These diodes can conduct a maximum current of 10 mA

without causing irreversible damage to the part.

VIN

VDD

30pF

4pF

CONVERSION PHASE - SWITCH OPEN

TRACK PHASE - SWITCH CLOSED

Figure 20. Equivalent Analog Input Circuit

Capacitor C1 in Figure 20 is typically about 4 pF and can

primarily be attributed to pin capacitance. Resistor R1 is a

lumped component made up of the on resistance (RON) of

a track-and-hold switch, and also the RON of the input multi-

plexer. The total resistor is typically about 400 Ω. C2, the ADC

sampling capacitor, has a typical capacitance of 30 pF.

VDD

VIN1

GND

5V SUPPLY

REF 19x

µF

0.1

µF

AD7992

0V to REFIN

INPUT

SDA

µC/µP

SCL

2-WIRE SERIAL

INTERFACE

CONVST

ALERT

VIN2/REFIN

SET TO REQUIRED

ADDRESS

0.1

µF

Figure 21. AD7992 Typical Connection Diagram, Single-Channel Mode, Mode 1

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