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AD7475 Datasheet(PDF) 7 Page  Analog Devices 

AD7475 Datasheet(HTML) 7 Page  Analog Devices 
7 / 16 page REV. A AD7475/AD7495 –7– PIN FUNCTION DESCRIPTIONS Pin No. Mnemonic Function 1 REF IN Reference Input for the AD7475. An external reference must be applied to this input. The voltage range for the external reference is 2.5 V ±1% for specified performance. A cap of a least 0.1 F should be placed on the REF IN pin. REF OUT Reference Output for the AD7495. A minimum 100 nF capacitance is required from this pin to GND. The internal reference can be taken from this pin but buffering is required before it is applied elsewhere in a system. 2VIN Analog Input. Singleended analog input channel. The input range is 0 to REF IN. 3 GND Analog Ground. Ground reference point for all circuitry on the AD7475/AD7495. All analog input signals and any external reference signal should be referred to this GND voltage. 4 SCLK Serial Clock. Logic input. SCLK provides the serial clock for accessing data from the part. This clock input is also used as the clock source for the AD7475/AD7495’s conversion process. 5 SDATA Data Out. Logic Output. The conversion result from the AD7475/AD7495 is provided on this output as a serial data stream. The bits are clocked out on the falling edge of the SCLK input. The data stream consists of four leading zeros followed by the 12 bits of conversion data which is provided MSB first. 6VDRIVE Logic Power Supply Input. The voltage supplied at this pin determines at what voltage the serial interface of the AD7475/AD7495 will operate. 7 CS Chip Select. Active low logic input. This input provides the dual function of initiating conversions on the AD7475/AD7495 and also frames the serial data transfer. 8VDD Power Supply Input. The VDD range for the AD7475/AD7495 is from 2.7 V to 5.25 V. TERMINOLOGY Integral Nonlinearity This is the maximum deviation from a straight line passing through the endpoints of the ADC transfer function. The endpoints of the transfer function are zero scale, a point 1/2 LSB below the first code transition, and full scale, a point 1/2 LSB above the last code transition. Differential Nonlinearity This is the difference between the measured and the ideal 1 LSB change between any two adjacent codes in the ADC. Offset Error This is the deviation of the first code transition (00 . . . 000) to (00 . . . 001) from the ideal, i.e., AGND + 0.5 LSB. Gain Error This is the deviation of the last code transition (111 . . . 110) to (111 . . . 111) from the ideal (i.e., VREF – 1.5 LSB) after the offset error has been adjusted out. Track/Hold Acquisition Time The track/hold amplifier returns into track mode on the 13th SCLK rising edge (see Serial Interface section). The Track/Hold Acquisition Time is the minimum time required for the track andhold amplifier to remain in track mode for its output to reach and settle to within 0.5 LSB of the applied input signal, given a step change to the input signal. Signal to (Noise + Distortion) Ratio This is the measured ratio of signal to (noise + distortion) at the output of the A/D converter. The signal is the rms amplitude of the fundamental. Noise is the sum of all nonfundamental signals up to half the sampling frequency (fS/2), excluding dc. The ratio is dependent on the number of quantization levels in the digiti zation process; the more levels, the smaller the quantization noise. The theoretical signal to (noise + distortion) ratio for an ideal Nbit converter with a sine wave input is given by: Signal to (Noise + Distortion) = (6.02 N + 1.76) dB Thus for a 12bit converter, this is 74 dB. Total Harmonic Distortion Total harmonic distortion (THD) is the ratio of the rms sum of harmonics to the fundamental. For the AD7475/AD7495, it is defined as: THD dB VVVVV V ( ) log = ++++ 20 2 2 3 2 4 2 5 2 6 2 1 where V1 is the rms amplitude of the fundamental and V2, V3, V4, V5 and V6 are the rms amplitudes of the second through the sixth harmonics. Peak Harmonic or Spurious Noise Peak harmonic or spurious noise is defined as the ratio of the rms value of the next largest component in the ADC output spectrum (up to fS/2 and excluding dc) to the rms value of the fundamental. Normally, the value of this specification is determined by the largest harmonic in the spectrum, but for ADCs where the har monics are buried in the noise floor, it will be a noise peak. Intermodulation Distortion With inputs consisting of sine waves at two frequencies, fa and fb, any active device with nonlinearities will create distortion products at sum and difference frequencies of mfa nfb where m, n = 0, 1, 2, 3, etc. Intermodulation distortion terms are those for which neither m nor n is equal to zero. For example, the second order terms include (fa + fb) and (fa – fb), while the third order terms include (2fa + fb), (2fa – fb), (fa + 2fb) and (fa – 2fb). The AD7475/AD7495 are tested using the CCIF standard where two input frequencies near the top end of the input bandwidth are used. In this case, the second order terms are usually distanced in frequency from the original sine waves while the third order terms are usually at a frequency close to the input frequencies. As a result, the second and third order terms are specified sepa rately. The calculation of the intermodulation distortion is as per the THD specification where it is the ratio of the rms sum of the individual distortion products to the rms amplitude of the sum of the fundamentals expressed in dBs. 
Similar Part No.  AD7475 

Similar Description  AD7475 


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