Datasheet AD7711A (Analog Devices) - 7

AD7711A PIN FUNCTION DESCRIPTIONS Pin Mnemonic Function
1 SCLK Serial Clock. Logic input/output, depending on the status of the MODE pin. When MODE is high, the device is in its self-clocking mode, and the SCLK pin provides a serial clock output. This SCLK becomes active when RFS or TFS goes low, and it goes high impedance when either RFS or TFS returns high or when the device has completed transmission of an output word. When MODE is low, the device is in its external clocking mode, and the SCLK pin acts as an input. This input serial clock can be a continuous clock with all
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data transmitted in a continuous train of pulses. Alternatively, it can be a noncontinuous clock with the information being transmitted to the AD7711A in smaller batches of data. 2 MCLK IN Master Clock Signal for the Device. This can be provided in the form of a crystal or external clock. A crystal can be tied across the MCLK IN and MCLK OUT pins. Alternatively, the MCLK IN pin can be driven with a CMOS compatible clock and MCLK OUT left unconnected. The clock input frequency is nominally 10 MHz. 3 MCLK OUT When the master clock for the device is a crystal, the crystal is connected between MCLK IN and MCLK OUT. 4 A0 Address Input. With this input low, reading and writing to the device is to the control register. With this input high, access is to either the data register or the calibration registers. 5 SYNC Logic Input. Allows for synchronization of the digital filters when using a number of AD7711As. It resets the nodes of the digital filter. 6 MODE Logic Input. When this pin is high, the device is in its self-clocking mode. With this pin low, the device is in its external clocking mode. 7 AIN1(+) Analog Input Channel 1. Positive input of the programmable gain differential analog input. The AIN1(+) input is connected to an output current source that can be used to check that an external transducer has burned out or gone open circuit. This output current source can be turned on/off via the control register. 8 AIN1(–) Analog Input Channel 1. Negative input of the programmable gain differential analog input. 9 AIN2(+) Analog Input Channel 2. Positive input of the programmable gain differential analog input. 10 AIN2(–) Analog Input Channel 2. Negative input of the programmable gain differential analog input. 11 VSS Analog Negative Supply, 0 V to –5 V. Tied to AGND for single-supply operation. The input voltage on AIN1 or AIN2 should not go > 30 mV negative w.r.t. VSS for correct operation of the device. 12 AVDD Analog Positive Supply Voltage, 5 V to 10 V. 13 VBIAS Input Bias Voltage. This input voltage should be set such that VBIAS + 0.85 ¥ VREF < AVDD and VBIAS – 0.85 ¥ VREF >VSS where VREF is REF IN(+) – REF IN(–). Ideally, this should be tied halfway between AVDD and VSS. Thus with AVDD = +5 V and VSS = 0 V, it can be tied to REF OUT; with AVDD = +5 V and VSS = –5 V, it can be tied to AGND while with AVDD = +10 V, it can be tied to +5 V. 14 REF IN(–) Reference Input. The REF IN(–) can lie anywhere between AVDD and VSS provided REF IN(+) is greater than REF IN(–). 15 REF IN(+) Reference Input. The reference input is differential provided REF IN(+) is greater than REF IN(–). REF IN(+) can lie anywhere between AVDD and VSS. 16 REF OUT Reference Output. The internal 2.5 V reference is provided at this pin. This is a single ended output that is referred to AGND. It is a buffered output that is capable of providing 1 mA to an external load. 17 RTD CURRENT Constant Current Output. A nominal 400 mA constant current is provided at this pin, and this can be used as the excitation current for RTDs. This current can be turned on/off via the control register. 18 AGND Ground Reference Point for Analog Circuitry. REV. D –7–