ADC AD-95 User Manual download pdf (Page 18)

AD7991/AD7995/AD7999

Rev. B | Page 18 of 28

TYPICAL CONNECTION DIAGRAM

Figure 22 shows the typical connection diagram for the

AD7991/AD7995/AD7999.

The reference voltage can be taken from the supply voltage,

. However, the AD7991/AD7995/AD7999 can be configured

to be a 3-channel device with the reference voltage applied to

the V

IN3

REF

pin. In this case, a 1 F decoupling capacitor on

the V

IN3

REF

pin is recommended.

SDA and SCL form the 2-wire I

C compatible interface. External

pull-up resistors are required for both the SDA and SCL lines.

The AD7991-0/AD7995-0 and the AD7991-1/AD7995-1/

AD7999-1 support standard, fast, and high speed I

C interface

modes. Both the -0 and -1 devices have independent I

C addresses,

which allows the devices to connect to the same I

C bus without

contention issues.

The part requires approximately 0.6 µs to wake up from power-

down and to acquire the analog input. Once the acquisition

phase ends, the conversion phase starts and takes approximately

1 µs to complete. The AD7991/AD7995/AD7999 enters

shutdown mode after each conversion, which is useful in

applications where power consumption is a concern.

ANALOG INPUT

Figure 21 shows an equivalent circuit of the AD7991/AD7995/

AD7999 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. If the signal does exceed this level,

the diodes become forward-biased and start conducting current

into the substrate. Each diode can conduct a maximum current

of 10 mA without causing irreversible damage to the part.

06461-023

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 can

primarily be attributed to pin capacitance. Resistor R1 is a

lumped component composed of the on resistance (R

) of

both a track-and-hold switch and the input multiplexer. The

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

sampling capacitor, has a typical capacitance of 30 pF.

IN0

5V SUPPLY

10µF 0.1µF

MICROCONTROLLER/

MICROPROCESSOR

2-WIRE SERIAL

INTERFACE

GND

AD7991/

AD7995/

AD7999

SDA

SCL

06461-024

IN1

IN2

IN3

REF

Figure 22. AD7991/AD7995/AD7999 Typical Connection Diagram

1 2 ... 13 14 15 16 17 18 19 20 21 22 23 ... 27 28

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ADC AD-95 User Manual Page 18

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