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
or
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 s, and conversion time is approximately 2 s. 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
D1
VDD
D2
R1
C2
30pF
C1
4pF
CONVERSION PHASE—SWITCH OPEN
TRACK PHASE—SWITCH CLOSED
03472-0-022
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 . C2, the
ADC sampling capacitor, has a typical capacitance of 30 pF.
VDD
VIN1
GND
5V SUPPLY
REF 19x
0.1
F
0.1
F
10
F
AD7993/
AD7994
0V to REFIN
INPUT
SDA
C/P
SCL
2-WIRE SERIAL
INTERFACE
CONVST
ALERT
REFIN
RP
VDD
AS
VIN4
03472-0-021
1
F
Figure 22. AD7993/AD7994 Typical Connection Diagram