TC826 datasheet(9/18 Pages) MICROCHIP

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DS21477B-page 9

TC826

The differential input voltage must be within the device

Common mode range when the converter and mea-

sured system share the same power supply common

(ground). If the converter and measured system do not

share the same power supply common, -IN should be

tied to analog common. This is the usual connection for

battery operated systems. Polarity is determined at the

end of signal integrate signal phase. The sign bit is a

true polarity indication, in that signals less than 1LSB

are correctly determined. This allows precision null

detection limited only by device noise and system

noise.

4.1.3

REFERENCE INTEGRATE CYCLE

The final phase is reference integrate or de-integrate.

-IN is internally connected to analog common and +IN

is connected with the correct polarity to cause the inte-

grator output to return to zero. The time required for the

output to return to zero is proportional to the input sig-

nal and is between 0 and 40 counts. The digital reading

displayed is:

EQUATION 4-2:

FIGURE 4-2:

CONVERSION HAS THREE PHASES

20 =

VIN

VREF

Internal

System

Clock (FSYS)

Auto-Zero Phase (AZ)

Signal Integrate

Phase (SI)

Reference Integrate Phase (RI)

(De-integrate)

Integrator

Output

Internal Data

Latch Update

Signal

19 Counts

Minimum

Counts

41 Counts

Maximum

TD ≈ VIN

Number of Counts

Proportional to

VIN

One Conversion Cycle = 80 Counts

(TCONV = 80 X

FSYS

)

True Zero

Crossing

Sign Bit Determined

Zero Crossing

Detected

Analog Common

Potential

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