AD7194 Datasheet, PDF (11/56 Pages) Analog Devices – 8-Channel, 4.8 kHz, Ultralow Noise, 24-Bit Sigma-Delta ADC with PGA

Pin No. Mnemonic
23
AVDD
24
DVDD
25
SYNC
26
NC
27
DOUT/RDY
28
DIN
29
MCLK1
30
MCLK2
31
SCLK
32
CS
AD7194
Description
Analog Supply Voltage, 3 V to 5.25 V. AVDD is independent of DVDD. Therefore, DVDD can be operated at 3 V
with AVDD at 5 V or vice versa.
Digital Supply Voltage, 2.7 V to 5.25 V. DVDD is independent of AVDD. Therefore, AVDD can be operated at 3 V
with DVDD at 5 V or vice versa.
Logic input that allows for synchronization of the digital filters and analog modulators when using a
number of AD7194 devices. While SYNC is low, the nodes of the digital filter, the filter control logic, and the
calibration control logic are reset, and the analog modulator is also held in its reset state. SYNC does not
affect the digital interface but does reset RDY to a high state if it is low. SYNC has a pull-up resistor
internally to DVDD.
This pin should be connected to GND for correct operation.
Serial Data Output/Data Ready Output. DOUT/RDY serves a dual purpose. It functions as a serial data
output pin to access the output shift register of the ADC. The output shift register can contain data from
any of the on-chip data or control registers. In addition, DOUT/RDY operates as a data ready pin, going low
to indicate the completion of a conversion. If the data is not read after the conversion, the pin goes high
before the next update occurs. The DOUT/RDY falling edge can be used as an interrupt to a processor,
indicating that valid data is available. With an external serial clock, the data can be read using the
DOUT/RDY pin. With CS low, the data-/control-word information is placed on the DOUT/RDY pin on the
SCLK falling edge and is valid on the SCLK rising edge.
Serial Data Input to the Input Shift Register on the ADC. Data in this shift register is transferred to the
control registers in the ADC, with the register selection bits of the communications register identifying the
appropriate register.
When the master clock for the device is provided externally by a crystal, the crystal is connected between
MCLK1 and MCLK2.
Master Clock Signal for the Device. The AD7194 has an internal 4.92 MHz clock. This internal clock can be
made available on the MCLK2 pin. The clock for the AD7194 can also be provided externally in the form of
a crystal or external clock. A crystal can be tied across the MCLK1 and MCLK2 pins. Alternatively, the MCLK2
pin can be driven with a CMOS-compatible clock and with the MCLK1 pin remaining unconnected.
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 nonconti-
nuous clock with the information transmitted to or from the ADC in smaller batches of data.
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.
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