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AD7991/AD7995/AD7999

Preliminary Technical Data

Rev.PrB | Page 16 of 25

TYPICAL CONNECTION DIAGRAM

Figure 13 shows the typical connection diagram for the

AD7991/AD7995/AD7999.

The reference voltage can be taken from the supply voltage VDD.

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

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

the VIN3/REFIN pin.

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

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

lines.

The AD7991/AD7995/AD7999-0 and the

AD7991/AD7995/AD7999-1 both support the standard, fast

and high speed I2C interface modes. Both the -0 and the -1

device will have an independent I2C address. This will allow

both device to connect to the same I2C bus without any

contention issues.

Wake up from power-down prior to a conversion is

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

The AD7991/AD7995/AD7999 enters shutdown mode again

after each conversion, which is useful in applications where

power consumption is a concern.

ANALOG INPUT

Figure 12 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. 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 12. Equivalent Analog Input Circuit

Capacitor C1 in Figure 12 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

VIN0

GND

+5V SUPPLY

0.1µF

10µF

AD7991/

AD7995/

AD7999

SDA

µC/µP

SCL

TWO WIRE SERIAL

INTERFACE

VIN3/Vref

VIN1

VIN2

Figure 13. AD7991/AD7995/AD7999 Typical Connection Diagram

AD7991 Datasheet(PDF) 16 Page - Analog Devices

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