AD7991 Analog Devices, AD7991 Datasheet - Page 18

• Manufacturer Part Number: AD7991
• Description: 4-Channel, 12-Bit ADC with I2C Compatible Interface in 8-Lead SOT-23
• Manufacturer: Analog Devices

Specifications of AD7991

• Resolution (bits): 12bit
• # Chan: 4
• Sample Rate: 140kSPS
• Interface: I²C/Ser 2-Wire
• Analog Input Type: SE-Uni
• Ain Range: Uni (Vref),Uni Vdd
• Adc Architecture: SAR
• Pkg Type: SOT

AD7991/AD7995/AD7999
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,
V
to be a 3-channel device with the reference voltage applied to
the V
the V
SDA and SCL form the 2-wire I
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
modes. Both the -0 and -1 devices have independent I
which allows the devices to connect to the same I
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.
DD
. However, the AD7991/AD7995/AD7999 can be configured
IN3
IN3
/V
/V
REF
REF
pin. In this case, a 1 μF decoupling capacitor on
pin is recommended.
2
C compatible interface. External
V
V
V
V
IN0
IN1
IN2
IN3
/V
REF
Figure 22. AD7991/AD7995/AD7999 Typical Connection Diagram
GND
AD7991/
AD7995/
AD7999
2
C bus without
2
2
C interface
C addresses,
V
DD
10µF
SDA
SCL
+
Rev. B | Page 18 of 28
0.1µF
+
R
P
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.
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
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.
R
P
V
IN
4pF
5V SUPPLY
C1
2-WIRE SERIAL
INTERFACE
MICROCONTROLLER/
MICROPROCESSOR
Figure 21. Equivalent Analog Input Circuit
V
DD
D1
D2
CONVERSION PHASE—SWITCH OPEN
TRACK PHASE—SWITCH CLOSED
R1
30pF
C2
ON
) of