Maxim-integrated MAXQ7667 Uživatelský manuál stáhnout pdf (Strana 243)

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MAXQ7667 User’s Guide

14.5.3 Unipolar/Bipolar

The MAXQ7667 ADC produces a digital output that corresponds to the differential analog input voltage as long as the differential ana-

log inputs are within the specified range. The analog inputs are configured for differential conversion when the SARDIF (SARC.8) con-

trol bit is set. When performing differential conversions, the control bit SARBIP (SARC.7) selects between unipolar and bipolar opera-

tion modes. Unipolar mode sets the differential input range from 0 to REF. A negative differential analog input in unipolar mode caus-

es the digital output code to be zero. Selecting bipolar mode sets the differential input range to -REF/2 to +REF/2. The digital output

code is straight binary in unipolar mode and two’s complement in bipolar mode.

In single-ended mode (SARDIF set to 0), the MAXQ7667 ADC analog inputs are internally referenced to AGND. Selecting unipolar

mode sets the full-scale input range to 0 to REF. Bipolar mode sets the full-scale input range to 0 to REF/2. As above, the digital out-

put code is straight binary in unipolar mode and two’s complement in bipolar mode.

Figure 14-3. Equivalent Input Circuit (Hold/Conversion Mode)

CONTROL

LOGIC

CAPACITIVE

DAC

AGND

AIN+

AIN-

IN+

IN-

IN+

IN-

COMP

Figure 14-2. Equivalent Input Circuit (Track/Acquisition Mode)