Datasheet AD7709 (Analog Devices) - 10

AD7709 PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Function
1 IOUT1 Output for Internal Excitation Current Source. Either current source IEXC1, IEXC2, IEXC3, or a combina- tion of the current sources, can be switched to this output. 2 IOUT2 Output for Internal Excitation Current Source. Either current source IEXC1, IEXC2, IEXC3, or a combina- tion of the current sources, can be switched to this output. 3 REFIN1(+) Positive Reference Input. REFIN1(+) can lie anywhere between VDD and GND + 1 V. The nominal refer- ence voltage (REFIN1(+) – REFIN1(–)) is 2.5 V, but the part is functional with a reference range from 1 V to VDD. 4 REFIN1(–) Negative Reference Input. This reference input can lie anywhere between GND and VDD – 1 V. 5 AIN1 Analog Input. Programmable gain input that can be used as a pseudo-differential input when used with AINCOM or as the positive input of a fully differential input pair when used with AIN2. 6 AIN2 Analog Input. Programmable gain input that can be used as a pseudo-differential input when used with AINCOM or as the negative input of a fully differential input pair when used with AIN1. 7 AIN3/P3 Analog Input/Digital Port Bit. Programmable gain input that can be used as a pseudo-differential input when used with AINCOM or as the positive input of a fully differential input pair when used with AIN4. This pin can also be programmed as a general-purpose digital input bit. 8 AIN4/P4 Analog Input/Digital Port Bit. Programmable gain input that can be used as a pseudo-differential input when used with AINCOM or as the negative input of a fully-differential input pair when used with AIN3. This pin can also be programmed as a general-purpose digital input bit. 9 AINCOM All analog inputs are referenced to this input when configured in pseudo-differential input mode. 10 REFIN2(+) Positive Reference Input. REFIN2(+) can lie anywhere between VDD and GND + 1 V. The nominal reference voltage (REFIN2(+) – REFIN2(–)) is 2.5 V, but the part is functional with a reference range from 1 V to VDD. 11 REFIN2(–) Negative Reference Input. This reference input can lie anywhere between GND and VDD – 1 V. 12 P2/SW2 Dual-Purpose Pin. It can act as a general-purpose output (P2) bit or as a low-side power switch (SW2) to PWRGND. 13 PWRGND Ground Point for the Low-Side Power Switches SW2 and SW1. PWRGND must be tied to GND. 14 P1/SW1 Dual-Purpose Pin. It can act as a general-purpose output (P1) bit or as a low-side power switch (SW1) to PWRGND. 15 RESET Digital Input Used to Reset the ADC to Its Power-On-Reset Status. This pin has a weak pull-up internally to VDD. 16 SCLK Serial Clock Input 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 AD7709 in smaller batches of data. A weak pull-up to VDD is provided on the SCLK input. 17 CS Chip Select Input. This is an active low logic input used to select the AD7709. CS can be used to select the AD7709 in systems with more than one device on the serial bus or as a frame synchronization signal in com- municating with the device. CS can be hardwired low allowing the AD7709 to operate in 3-wire mode with SCLK, DIN, and DOUT used to interface with the device. A weak pull-up to VDD is provided on the CS input. 18 RDY RDY is a Logic Low Status Output from the AD7709. RDY is low if the ADC has valid data in its data register. This output returns high on completion of a read operation from the data register. If data is not read, RDY will return high prior to the next update indicating to the user that a read operation should not be initiated. 19 DOUT Serial Data Output Accessing the Output Shift Register of the AD7709. The output shift register can contain data from any of the on-chip data or control registers. 20 DIN Serial Data Input Accessing the Input Shift Register on the AD7709. Data in this shift register is transferred to the control registers within the ADC, the selection bits of the communications register selecting which control register. A weak pull-up to VDD is provided on the DIN input. 21 GND Ground Reference Point for the AD7709 22 VDD Supply Voltage, 3 V or 5 V Nominal 23 XTAL2 Output from the 32.768 kHz Crystal Oscillator Inverter 24 XTAL1 Input to the 32.768 kHz Crystal Oscillator Inverter REV. A –9– Document Outline FEATURES INTERFACE POWER ON-CHIP FUNCTIONS APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS SPECIFICATIONS TIMING CHARACTERISTICS ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION ORDERING GUIDE PIN FUNCTION DESCRIPTIONS Typical Performance Characteristics ADC CIRCUIT INFORMATION Overview Sigma-Delta ADC NOISE PERFORMANCE ON-CHIP REGISTERS Communications Register (A1, A0 = 0, 0) Status Register (A1, A0 = 0, 0; Power-On-Reset = 00H) Configuration Register (A1, A0 = 0, 1; Power-On-Reset = 000007H) Filter Register (A1, A0 = 1, 0; Power-On-Reset = 45h) ADC Data Result Register (A1, A0 = 1, 1; Power-On-Reset = 0000h CONFIGURING THE AD7709 DIGITAL INTERFACE MICROCOMPUTER/MICROPROCESSOR INTERFACING AD7709-to-68HC11 Interface AD7709-to-8051 Interface AD7709-to-ADSP-2103/ADSP-2105 Interface CIRCUIT DESCRIPTION Analog Input Channels Programmable Gain Amplifier Bipolar/Unipolar Configuration Data Output Coding Excitation Currents Crystal Oscillator Reference Input Reset Input Power-Down Mode Grounding and Layout APPLICATIONS Pressure Measurement Temperature Measurement 3-Wire RTD Configurations Smart Transmitters OUTLINE DIMENSIONS Revision History