AD7274 datasheet(15/20 Pages) AD

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PRELIMINARYTECHNICALDATA

Preliminary Technical Data

AD7273/AD7274

TYPICAL CONNECTION DIAGRAM

Figure 10 shows a typical connection diagram for the

AD7273/AD7274. An external reference must be applied

to the ADC. This reference can be in the range of 1.2V to

VDD. A precision reference like the REF19X family or the

ADR421 can be used to supply the reference voltage to the

AD7273/AD7274.

The conversion result is output in a 16-bit word with two

leading zeros followed by the 12-bit or 10-bit result. The

12-bit result from the AD7274 will be followed by two

trailing zeros and the 10-bit result from the AD7273 will

be followed by four trailing zeros.

Figure 10. AD7273/AD7274 Typical Connection Diagram

Table I provides some typical performance data with

various references under the same set-up conditions.

Voltage

AD7274 SNR Performance

Reference

TBD kHz Input

AD780@2.5V

TBD dB

REF192

TBD dB

ADR421

TBD dB

ADR291

TBD dB

Table I. AD7274 performance for various Voltage

References IC

Analog Input

Figure 11 shows an equivalent circuit of the analog input

structure of the AD7273/AD7274. The two diodes D1 and

D2 provide ESD protection for the analog inputs. Care

must be taken to ensure that the analog input signal never

exceeds the supply rails by more than 300mV. This will

cause these diodes to become forward biased and start

conducting current into the substrate. 10mA is the maxi-

mum current these diodes can conduct without causing

irreversable damage to the part. The capacitor C1 in

Figure 11 is typically about 4pF and can primarily be

attributed to pin capacitance. The resistor R1 is a lumped

component made up of the on resistance of a switch. This

resistor is typically about TBD

Ω. The capacitor C2 is the

ADC sampling capacitor and has a capacitance of TBD

pF typically. For ac applications, removing high

frequency components from the analog input signal is

recommended by use of a bandpass filter on the relevant

analog input pin. In applications where harmonic distor-

tion and signal to noise ratio are critical, the analog input

should be driven from a low impedance source. Large

source impedances will significantly affect the ac perfor-

mance of the ADC. This may necessitate the use of an

input buffer amplifier. The choice of the op-amp will be a

function of the particular application.

Figure 11. Equivalent Analog Input Circuit

VIN

VDD

TBD PF

4pF

CONVERSION PHASE - SWITCH OPEN

TRACK PHASE - SWITCH CLOSED

+3.6V

SUPPLY

0.1µF

10µF

TBD mA

VDD

0.1µF

1µF

TANT

REF192

+2.5V

VIN

GND

0V toVREF

INPUT

SDATA

DSP/

µC/µP

SCLK

SERIAL

INTERFACE

AD7274/

AD7273

VREF

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