Datasheet

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SBAS253E − MAY 2003 − REVISED JULY 2006

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2.2.6 Transition Noise

The transition noise of the ADS7869 itself is low, as shown in Figure 1−5. Applying a low-noise DC input and

initiating 8000 conversions generated this histogram.

Code (decimal)

Number of Occurrences

10000

8000

6000

4000

2000

7986

3030 3031 3032 3033 3034

013 1 0

Figure 1−5. Histogram of 8000 Conversions

2.3 Sign Comparators

The ADS7869 includes two sets of sign comparators that differ in their hysteresis. The first set, which is used

for the position sensor inputs in motor control applications, is connected to the inputs A1, B1, A2, and B2. The

hysteresis of these comparators is typically 75mV. In motor control applications, these comparators are used

to measure the signs of the position sensor input signals.

The second set is in parallel to the window comparators at the U_C, V_C, and W_C pins. The hysteresis of

these components is typically 10mV. In motor control applications, these comparators are used to measure

the sign of the main currents.

The sign comparator switches from 0 to 1 if the differential input voltage is above +1/2 of the hysteresis. If the

output is 1, the sign comparator switches back to 0 if the differential input voltage is below −1/2 of the

hysteresis. See Figure 1−6.

+Half Hysteresis

−

Half Hysteresis

Comparator

Output

Figure 1−6. Typical Transfer Function of a Sign Comparator