Datasheet AD7821 (Analog Devices)

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LC2MOS High Speed,
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P Compatible 8-Bit ADC with Track/Hold Function AD7821 FEATURES FUNCTIONAL BLOCK DIAGRAM Fast Conversion Time: 660 ns Max 100 kHz Track-and-Hold Function 1 MHz Sample Rate Unipolar and Bipolar Input Ranges Ratiometric Reference Inputs No External Clock Extended Temperature Range Operation Skinny 20-Lead DlPs, SOIC, and 20-Terminal Surface-Mount Packages GENERAL DESCRIPTION PRODUCT HIGHLIGHTS
The AD7821 is a high speed, 8-bit, sampling, analog-to-digital 1. Fast Conversion Time converter that offers improved performance over the popular The half-flash conversion technique, coupled with fabrication AD7820. It offers a conversion time of 660 ns (versus 1.36 µs on Analog Devices’ LC2MOS process, enables a very fast con- for the AD7820) and 100 kHz signal bandwidth (versus 6.4 version time. The conversion time for the WR-RD mode is kHz). The sampling instant is better defined and occurs on the 660 ns, with 700 ns for the RD mode. falling edge of WR or RD. The provision of a VSS pin (Pin 19) 2. Built-In Track-and-Hold allows the part to operate from ± 5 V supplies and to digitize This allows input signals with slew rates up to 1.6 V/µs to be bipolar input signals. Alternatively, for unipolar inputs, the VSS pin converted to 8 bits without an external track-and-hold. This can be grounded and the AD7821 will operate from a single +5 V corresponds to a 5 V peak-to-peak, 100 kHz sine wave signal. supply, like the AD7820. 3. Total Unadjusted Error The AD7821 has a built-in track-and-hold function capable of The AD7821 features an excellent total unadjusted error figure digitizing full-scale signals up to 100 kHz max. It also uses a of less than ±1 LSB over the full operating temperature range. half-flash conversion technique that eliminates the need to gen- erate a CLK signal for the ADC. 4. Unipolar/Bipolar Input Ranges The AD7821 is specified for single-supply (+5 V) operation The AD7821 is designed with standard microprocessor control with a unipolar full-scale range of 0 to +5 V, and for dual-supply signals (CS, RD, WR, RDY, INT) and latched, three-state data (±5 V) operation with a bipolar input range of ±2.5 V. Typical outputs capable of interfacing to high speed data buses. An performance characteristics are given for other input ranges. overflow output (OFL) is also provided for cascading devices to achieve higher resolution. 5. Dynamic Specifications for DSP Users In addition to the traditional ADC specifications, the The AD7821 is fabricated in Linear Compatible CMOS AD7821 is specified for ac parameters, including signal-to- (LC2MOS), an advanced, mixed technology process combining noise ratio, distortion, and slew rate. precision bipolar circuits with low power CMOS logic. The part features a low power dissipation of 50 mW. REV. B Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that
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Document Outline FEATURES GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM PRODUCT HIGHLIGHTS SPECIFICATIONS Test Circuits ORDERING GUIDE ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATIONS PIN FUNCTION DESCRIPTIONS TERMINOLOGY LEAST SIGNIFICANT BIT (LSB) TOTAL UNADJUSTED ERROR SLEW RATE TOTAL HARMONIC DISTORTION INTERMODULATION DISTORTION SIGNAL-TO-NOISE RATIO PEAK HARMONIC OR SPURIOUS NOISE Typical Performance Characteristics CIRCUIT INFORMATION BASIC DESCRIPTION OPERATING SEQUENCE REFERENCE AND INPUT INPUT CURRENT INPUT TRANSIENTS INHERENT TRACK-AND-HOLD SINUSOIDAL INPUTS DIGITAL SIGNAL PROCESSING APPLICATIONS SIGNAL-TO-NOISE RATIO AND DISTORTION EFFECTIVE NUMBER OF BITS INTERMODULATION DISTORTION HISTOGRAM PLOT DIGITAL INTERFACE RD Mode (MODE = 0) WR-RD Mode (MODE = 1) MICROPROCESSOR INTERFACING AD7821 – 68008 INTERFACE AD7821 – 8088 INTERFACE AD7821 – TMS32010 INTERFACE AD7821 – 8051 INTERFACE APPLYING THE AD7821 UNIPOLAR OPERATION BIPOLAR OPERATION 16-CHANNEL TELECOM A/D CONVERTER SIMULTANEOUS SAMPLING ADCS OUTLINE DIMENSIONS Revision History