Datasheet AD7866 (Analog Devices) - 7

AD7866 PIN CONFIGURATION REF SELECT 1 20 A0 2 19 DCAPB CS AGND 3 18 SCLK V 4 17 B2 VDRIVE VB1 5 16 AD7866 DOUTB TOP VIEW V 6 15 A2 D (Not to Scale) OUTA V 7 14 A1 DGND AGND 8 13 DVDD D 9 12 CAPA AVDD V 10 11 REF RANGE PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Function
1 REF SELECT Internal/External Reference Selection. Logic input. If this pin is tied to GND, the on-chip 2.5 V reference is used as the reference source for both ADC A and ADC B. In addition, pins VREF, DCAPA, and DCAPB must be tied to decoupling capacitors. If the REF SELECT pin is tied to a logic high, an external refer- ence can be supplied to the AD7866 through the VREF pin, in which case decoupling capacitors are required on DCAPA and DCAPB. However, if the VREF pin is tied to AGND while REF SELECT is tied to a logic low, an individual external reference can be applied to both ADC A and ADC B through pins DCAPA and DCAPB, respectively. See the Reference Configuration Options section. 2, 9 DCAPB, DCAPA Decoupling capacitors are connected to these pins to decouple the reference buffer for each respective ADC. The on-chip reference can be taken from these pins and applied externally to the rest of a system. Depending on the polarity of the REF SELECT pin and the configuration of the VREF pin, these pins can also be used to input a separate external reference to each ADC. The range of the external reference is dependent on the analog input range selected. See the Reference Configuration Options section. 3, 8 AGND Analog Ground. Ground reference point for all analog circuitry on the AD7866. All analog input signals and any external reference signal should be referred to this AGND voltage. Both of these pins should connect to the AGND plane of a system. The AGND and DGND voltages ideally should be at the same potential and must not be more than 0.3 V apart, even on a transient basis. 4, 5 VB2, VB1 Analog Inputs of ADC B. Single-ended analog input channels. The input range on each channel is 0 V to VREF or a 2 VREF range depending on the polarity of the RANGE pin upon the falling edge of CS. 6, 7 VA2, VA1 Analog Inputs of ADC A. Single-ended analog input channels. The input range on each channel is 0 V to VREF or a 2 VREF range depending on the polarity of the RANGE pin upon the falling edge of CS. 10 VREF Reference Decoupling and External Reference Selection. This pin is connected to the internal reference and requires a decoupling capacitor. The nominal reference voltage is 2.5 V, which appears at the pin; however, if the internal reference is to be used externally in a system, it must be taken from either the DCAPA or DCAPB pins. This pin is also used in conjunction with the REF SELECT pin when applying an external reference to the AD7866. See the REF SELECT pin description. –6– REV. A Document Outline FEATURES GENERAL DESCRIPTION PRODUCT HIGHLIGHTS FUNCTIONAL BLOCK DIAGRAM SPECIFICATIONS TIMING SPECIFICATIONS ABSOLUTE MAXIMUM RATINGS ORDERING GUIDE PIN CONFIGURATION PIN FUNCTION DESCRIPTIONS TERMINOLOGY Integral Nonlinearity Differential Nonlinearity Offset Error Offset Error Match Gain Error Gain Error Match Zero Code Error Zero Code Error Match Positive Gain Error Negative Gain Error Track-and-Hold Acquisition Time Signal-to-(Noise + Distortion) Ratio (SNDR) Total Harmonic Distortion (THD) Peak Harmonic or Spurious Noise Intermodulation Distortion Channel-to-Channel Isolation PSR (Power Supply Rejection) PERFORMANCE CURVES Typical Performance Characteristics CIRCUIT INFORMATION CONVERTER OPERATION ANALOG INPUT Analog Input Ranges Handling Bipolar Input Signals Transfer Functions Digital Inputs REFERENCE CONFIGURATION OPTIONS MODES OF OPERATION Normal Mode Partial Power-Down Mode Full Power-Down Mode POWER-UP TIMES POWER VS. THROUGHPUT RATE SERIAL INTERFACE MICROPROCESSOR INTERFACING AD7866 to ADSP-218x AD7866 to TMS320C541 AD7866 to DSP-563xx APPLICATION HINTS Grounding and Layout Evaluating the AD7866 Performance OUTLINE DIMENSIONS Revision History