AD7711AR-REEL7 데이터 시트보기 (PDF) - Analog Devices

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AD7711AR-REEL7

LC2MOS Signal Conditioning ADC with RTD Excitation Currents

Analog Devices 

AD7711

Pin Mnemonic

20 RFS

21 DRDY

22 SDATA

23 DVDD

24 DGND

Function

Receive Frame Synchronization. Active low logic input used to access serial data from the device. In the

self-clocking mode, the SCLK and SDATA lines both become active after RFS goes low. In the external

clocking mode, the SDATA line becomes active after RFS goes low.

Logic Output. A falling edge indicates that a new output word is available for transmission. The DRDY pin

will return high upon completion of transmission of a full output word. DRDY is also used to indicate

when the AD7711 has completed its on-chip calibration sequence.

Serial Data. Input/output with serial data being written to either the control register or the calibration

registers and serial data being accessed from the control register, calibration registers, or the data register.

During an output data read operation, serial data becomes active after RFS goes low (provided DRDY is

low). During a write operation, valid serial data is expected on the rising edges of SCLK when TFS is low.

The output data coding is natural binary for unipolar inputs and offset binary for bipolar inputs.

Digital Supply Voltage, 5 V. DVDD should not exceed AVDD by more than 0.3 V in normal operation.

Ground Reference Point for Digital Circuitry.

TERMINOLOGY

Intergral Nonlinearity

This is the maximum deviation of any code from a straight line

passing through the endpoints of the transfer function. The end-

points of the transfer function are zero-scale (not to be confused

with bipolar zero), a point 0.5 LSB below the first code transi-

tion (000 . . . 000 to 000 . . . 001) and full scale, a point 0.5 LSB

above the last code transition (111 . . . 110 to 111 . . . 111). The

error is expressed as a percentage of full scale.

Positive Full-Scale Error

Positive full-scale error is the deviation of the last code transi-

tion (111 . . . 110 to 111 . . . 111) from the ideal input full-scale

voltage. For AIN1(+), the ideal full-scale input voltage is

(AIN1(–) + VREF/GAIN – 3/2 LSBs); for AIN2, the ideal full-

scale input voltage is VREF/GAIN – 3/2 LSBs. It applies to both

unipolar and bipolar analog input ranges.

Unipolar Offset Error

Unipolar offset error is the deviation of the first code transition

from the ideal voltage. For AIN1(+), the ideal input voltage is

(AIN1(–) + 0.5 LSB); for AIN2, the ideal input is 0.5 LSB

when operating in the unipolar mode.

Bipolar Zero Error

This is the deviation of the midscale transition (0111 . . . 111

to 1000 . . . 000) from the ideal input voltage. For AIN1(+), the

ideal input voltage is (AIN1(–) – 0.5 LSB); for AIN2, the ideal

input is – 0.5 LSB when operating in the bipolar mode.

Bipolar Negative Full-Scale Error

This is the deviation of the first code transition from the ideal

input voltage. For (AIN1(+), the ideal input voltage is (AIN1(–)

– VREF/GAIN + 0.5 LSB); for AIN2 the ideal input is – VREF/GAIN

+ 0.5 LSB when operating in the bipolar mode.

Positive Full-Scale Overrange

Positive full-scale overrange is the amount of overhead avail-

able to handle input voltages on the AIN1(+) input greater

than AIN1(–) + VREF/GAIN or on the AIN2 input greater

than + VREF/GAIN (for example, noise peaks or excess

voltages due to system gain errors in system calibration rou-

tines) without introducing errors due to overloading the analog

modulator or to overflowing the digital filter.

Negative Full-Scale Overrange

This is the amount of overhead available to handle voltages on

AIN1(+) below AIN1(–) – VREF/GAIN or on AIN2 below

–VREF/GAIN without overloading the analog modulator or over-

flowing the digital filter. Note that the analog input will accept

negative voltage peaks on AIN1(+) even in the unipolar mode

provided that AIN1(+) is greater than AIN1(–) and greater than

VSS – 30 mV.

Offset Calibration Range

In the system calibration modes, the AD7711 calibrates its

offset with respect to the analog input. The offset calibration

range specification defines the range of voltages that the AD7711

can accept and still calibrate offset accurately.

Full-Scale Calibration Range

This is the range of voltages that the AD7711 can accept in the

system calibration mode and still calibrate full-scale correctly.

Input Span

In system calibration schemes, two voltages applied in sequence

to the AD7711’s analog input define the analog input range.

The input span specification defines the minimum and maxi-

mum input voltages from zero- to full-scale that the AD7711

can accept and still calibrate gain accurately.

–8–

REV. G

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