AD7785 Analog Devices, AD7785 Datasheet - Page 9

• Manufacturer Part Number: AD7785
• Description: 3-Channel, Low Noise, Low Power, 20-Bit ?-? ADC with On-Chip In-Amp and Reference
• Manufacturer: Analog Devices

Specifications of AD7785

• Resolution (bits): 20bit
• # Chan: 3
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± (Vref/Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
Table 4. Pin Function Descriptions
Pin No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Mnemonic
SCLK
CLK
CS
IOUT1
AIN1(+)
AIN1(−)
AIN2(+)
AIN2(−)
REFIN(+)/AIN3(+)
REFIN(−)/AIN3(−)
IOUT2
GND
AV
DV
DD
DD
Description
Serial Clock Input. This serial clock input is for data transfers to and from the ADC. The SCLK has a Schmitt-
triggered input, making the interface suitable for opto-isolated applications. The serial clock can be
continuous with all data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous
clock with the information being transmitted to or from the ADC in smaller batches of data.
Clock In/Clock Out. The internal clock can be made available at this pin. Alternatively, the internal clock can
be disabled, and the ADC can be driven by an external clock. This allows several ADCs to be driven from a
common clock, allowing simultaneous conversions to be performed.
Chip Select Input. This is an active low logic input used to select the ADC. CS can be used to select the ADC
in systems with more than one device on the serial bus or as a frame synchronization signal in communicating
with the device. CS can be hardwired low, allowing the ADC to operate in 3-wire mode with SCLK, DIN, and
DOUT used to interface with the device.
Output of Internal Excitation Current Source. The internal excitation current source can be made available at
this pin. The excitation current source is programmable so that the current can be 10 μA, 210 μA, or 1 mA.
Either IEXC1 or IEXC2 can be switched to this output.
Analog Input. AIN1(+) is the positive terminal of the differential analog input pair AIN1(+)/AIN1(−).
Analog Input. AIN1(−) is the negative terminal of the differential analog input pair AIN1(+)/AIN1(−).
Analog Input. AIN2(+) is the positive terminal of the differential analog input pair AIN2(+)/AIN2(−).
Analog Input. AIN2(−) is the negative terminal of the differential analog input pair AIN2(+)/AIN2(−).
Positive Reference Input/Analog Input. An external reference can be applied between REFIN(+) and
REFIN(−). REFIN(+) can lie anywhere between AV
REFIN(+) − REFIN(−) is 2.5 V, but the part functions with a reference from 0.1 V to AV
pin can function as AIN3(+) where AIN3(+) is the positive terminal of the differential analog input pair
AIN3(+)/AIN3(−).
Negative Reference Input/Analog Input. REFIN(−) is the negative reference input for REFIN. This reference
input can lie anywhere between GND and AV
negative terminal of the differential analog input pair AIN3(+)/AIN3(−).
Output of Internal Excitation Current Source. The internal excitation current source can be made available at
this pin. The excitation current source is programmable so that the current can be 10 μA, 210 μA, or 1 mA.
Either IEXC1 or IEXC2 can be switched to this output.
Ground Reference Point.
Supply Voltage, 2.7 V to 5.25 V.
Digital Interface Supply Voltage. The logic levels for the serial interface pins are related to this supply, which
is between 2.7 V and 5.25 V. The DV
equal 5 V with DV
AIN1(+)
AIN1(–)
AIN2(+)
AIN2(–)
DD
IOUT1
SCLK
CLK
at 3 V or vice versa.
CS
1
2
3
4
5
6
7
8
Figure 5. Pin Configuration
(Not to Scale)
AD7785
TOP VIEW
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DD
voltage is independent of the voltage on AV
16
15
14
13
12
11
10
9
DIN
DOUT/RDY
DV
AV
GND
IOUT2
REFIN(–)/AIN3(–)
REFIN(+)/AIN3(+)
DD
DD
DD
− 0.1 V. This pin also functions as AIN3(−), which is the
DD
and GND + 0.1 V. The nominal reference voltage
DD
DD
; therefore, AV
. Alternatively, this
AD7785
DD
can