AD7705 Data Acquisition Module

Pin

Function

SCLK

Serial Clock. An external serial clock is applied to the Schmitt-triggered logic input to access serial data from the AD7705/AD7706. This serial clock can be a continuous clock with all data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous clock with the information transmitted to the AD7705/AD7706 in smaller batches of data.

MCLK IN

Master Clock Signal. This can be provided in the form of a crystal/resonator or external clock. A crystal/resonator can be tied across the Pin MCLK IN and Pin MCLK OUT. Alternatively, the MCLK IN pin can be driven with a CMOS-compatible clock with the MCLK OUT pin left unconnected. The parts can be operated with clock frequencies in the range of 500 kHz to 5 MHz.

MCLK OUT

When the master clock for these devices is a crystal/resonator, the crystal/resonator is connected between Pin MCLK IN and Pin MCLK OUT. If an external clock is applied to Pin MCLK IN, Pin MCLK OUT provides an inverted clock signal. This clock can be used to provide a clock source for external circuitry and is capable of driving 1 CMOS load. If the user does not require this clock externally, Pin MCLK OUT can be turned off via the CLKDIS bit of the clock register. This ensures that the part does not unnecessarily burn power driving capacitive loads on Pin MCLK OUT.

Chip Select. Active low logic input used to select the AD7705/AD7706. With this input hardwired low, the AD7705/AD7706 can operate in its 3-wire interface mode with Pin SCLK, Pin DIN, and Pin DOUT used to interface to the device. The CS pin can be used to select the device communicating with the AD7705/AD7706.

Logic Input. Active low input that resets the control logic, interface logic, calibration coefficients, digital filter, and analog modulator of the parts to power-on status.

AIN2(+)

Positive Input of the Differential Analog Input Pair AIN2(+)/AIN2(−) for AD7705. Channel 1 for AD7706. 

AIN2(-)

Negative Input of the Differential Analog Input Pair AIN2(+)/AIN2(−) for AD7705. Channel 3 for AD7706.

AIN1(+)

Positive Input of the Differential Analog Input Pair AIN1(+)/AIN1(−) for AD7705. Channel 2 for AD7706.

AIN1(-)

Negative Input of the Differential Analog Input Pair AIN1(+)/AIN1(−) for AD7705. COMMON input for AD7706 with Channel 1, Channel 2, and Channel 3 referenced to this input.

REFIN(+)

Reference Input. Positive input of the differential reference input to the AD7705/AD7706. The referenceinput is differential with the provision that REF IN(+) must be greater than REF IN(−).REF IN(+) can lie anywhere between VDD and GND.

REFIN(-)

Reference Input. Negative input of the differential reference input to the AD7705/AD7706. The REF IN(−) can lie anywhere between VDD and GND, provided that REF IN(+) is greater than REF IN(−).

Logic Output. A logic low on this output indicates that a new output word is available from the AD7705/AD7706 data register. The DRDY pin returns high upon completion of a read operation of a full output word. If no data read has taken place between output updates, the DRDY line returns high for 500 × tCLK IN cycles prior to the next output update. While DRDY is high, a read operation should neither be attempted nor in progress to avoid reading from the data register as it is being updated. The DRDY line returns low after the update has taken place. DRDY is also used to indicate when the AD7705/AD7706 has completed its on-chip calibration sequence.

DOUT

Serial Data Output. Serial data is read from the output shift register on the part. The output shift register can contain information from the setup register, communication register, clock register, or data register, depending on the register selection bits of the communication register.

DIN

Serial Data Input. Serial data is written to the input shift register on the part. Data from the input shift register is transferred to the setup register, clock register, or communication register, depending on the register selection bits of the communication register.

VDD

Supply Voltage. 2.7 V to 5.25 V operation.

GND

The ground potential reference point of the internal circuit.