AD7821

REV. A

–4–

ABSOLUTE MAXIMUM RATINGS*

Digital Input Voltage to GND

Digital Output Voltage to GND

Operating Temperature Range

Commercial (K Version) . . . . . . . . . . . . . . –40

°C to +85°C

Industrial (B Version) . . . . . . . . . . . . . . . . –40

°C to +85°C

Extended (T Version) . . . . . . . . . . . . . . . –55

°C to +125°C

Storage Temperature Range . . . . . . . . . . . . –65

°C to +150°C

Lead Temperature (Soldering, 10 secs) . . . . . . . . . . . +300

°C

Power Dissipation (Any Package) to +75

°C . . . . . . . . 450 mW

Derates above +75

°C by . . . . . . . . . . . . . . . . . . . . . 6 mW/°C

*Stresses above those listed under “Absolute Maximum Ratings” may cause

permanent damage to the device. This is a stress rating only and functional

operation of the device at these or any other conditions above those indicated in the

operational sections of this specification is not implied. Exposure to absolute

maximum rating conditions for extended periods may affect device reliability.

TERMINOLOGY

LEAST SIGNIFICANT BIT (LSB)

An ADC with 8-bit resolution can resolve one part in 2

of full scale). For the AD7821 operating in either the unipolar

or bipolar input range with 5 V full scale, one LSB is 19.53 mV.

TOTAL UNADJUSTED ERROR

This is a comprehensive specification which includes relative

accuracy, offset error and full-scale error.

SLEW RATE

Slew Rate is the maximum allowable rate of change of input

signal such that the digital sample values are not in error.

TOTAL HARMONIC DISTORTION

Total harmonic distortion is the ratio of the square root of the

sum of the squares of the rms value of the harmonics to the rms

value of the fundamental. For the AD7821, total harmonic dis-

tortion (THD) is defined as

20 log

3

5

6

2

()

























dB

INTERMODULATION DISTORTION

With inputs consisting of sine waves at two frequencies, fa and

fb, any active device with nonlinearities will create distortion

products, of order (m+n), at sum and difference frequencies of

mfa+nfb, where m, n = 0, 1, 2, 3,- - - -. Intermodulation terms

are those for which m or n is not equal to zero. For example, the

second order terms include (fa + fb) and (fa – fb), and the third

order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and

(fa – 2fb). For the AD7821 intermodulation distortion is calcu-

lated separately for both the second and third order terms.

SIGNAL-TO-NOISE RATIO

Signal-to-noise ratio (SNR) is measured signal-to-noise at the

output of the ADC. The signal is the rms magnitude of the fun-

damental. Noise is the rms sum of all nonfundamental signals

(excluding dc) up to half the sampling frequency. SNR is de-

pendent on the number of quantization levels used in the digiti-

zation process. The theoretical SNR for a sine wave input is

given by:

SNR = (6.02 N + 1.76) dB

where N is the number of bits in the ADC. Thus, for an ideal

8-bit ADC, SNR = 50 dB.

PEAK HARMONIC OR SPURIOUS NOISE

Peak harmonic or spurious noise is the rms value of the largest

nonfundamental frequency (excluding dc) up to half the sam-

pling frequency to the rms value of the fundamental.

PIN CONFIGURATIONS

DIP AND SOIC

LCCC

PLCC

WARNING!

ESD SENSITIVE DEVICE

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily

accumulate on the human body and test equipment and can discharge without detection.

Although the AD7821 features proprietary ESD protection circuitry, permanent damage may

occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD

precautions are recommended to avoid performance degradation or loss of functionality.