AD7993 datasheet(16/32 Pages) AD

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AD7993/AD7994

Rev. 0 | Page 16 of 32

TYPICAL CONNECTION DIAGRAM

Figure 22 shows the typical connection diagram for the AD7993/

AD7994. In Figure 22 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 AD7993/AD7994 devices on the

same serial bus. An external reference must be applied to the

AD7993/AD7994. This reference can be in the range of 1.2 V to

VDD. A precision reference like the REF 19x family, AD780,

ADR03, or ADR381 can be used to supply the reference voltage

to the ADC.

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

face. External pull-up resisters are required for both SDA and

SCL lines.

The AD7993-0/AD7994-0 support standard and fast I2C

interface modes. The AD7993-1/AD7994-1 support standard,

fast, and high speed I2C interface modes. Therefore, if operating

the AD7993/AD7994 in either standard or fast mode, up to five

AD7993/AD7994 devices can be connected to the bus as noted:

3 × AD7993-0/AD7994-0 and 2 × AD7993-1/ AD7994-1

3 × AD7993-1/AD7994-1 and 2 × AD7994-0/AD7993-0

In high speed mode, up to three AD7993-1/AD7994-1 devices

can be connected to the bus.

Wake-up from shutdown prior to a conversion is approximately

1 µs, and conversion time is approximately 2 µs. The AD7993/

AD7994 enter shutdown mode again after each conversion,

which is useful in applications where power consumption is

a concern.

ANALOG INPUT

Figure 21 shows an equivalent circuit of the AD7993/AD7994’s

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 21. Equivalent Analog Input Circuit

Capacitor C1 in Figure 21 is typically about 4 pF and primarily

can be attributed to pin capacitance. Resistor R1 is a lumped

component made up of the on resistance (RON) of a switch

(track-and-hold switch), and also includes the RON of the input

multiplexer. 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

0.1

µF

0.1

µF

AD7993/

AD7994

0V to REFIN

INPUT

SDA

µC/µP

SCL

2-WIRE SERIAL

INTERFACE

CONVST

ALERT

REFIN

VDD

VIN4

µF

Figure 22. AD7993/AD7994 Typical Connection Diagram

AD7993 Datasheet(PDF) 16 Page - Analog Devices

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