Datasheet

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SBAS253E − MAY 2003 − REVISED JULY 2006
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2.4 Window Comparators
The window comparators test if the input voltage is within a certain range; this range is ±(voltage applied to
DAIN, pin 30). If the differential input voltage remains within this range, then the output of the window
comparator is 1. If the voltage is outside this range, then the output is set to 0. The window comparator has
a hysteresis that is turned on when the output is 0. The comparator outputs switch back to 1 when the input
voltage is within in the range of ±(DAIN −60mV). (See Figure 1−9.) The voltage at DAIN needs to be in a range
of 0.5V to 2.5V.
The window comparator has a switched capacitor circuitry, similar to the ADC architecture, but different from
other window comparators. This design dramatically increases the accuracy; due to the additional accuracy,
a proper front-end of the input signal is required. (See the Window Comparator Inputs section.)
+DAIN
DAIN
−
60mV
−
DAIN
+
60mV
−
DAIN
Comparator
Output
0V
Figure 1−9. Typical Transfer Function of a Window Comparator
Two clock cycles are used to sample the inputs. The next two clock cycles are used to test the lower and the
upper voltage limit. Every four clock cycles (or every 250ns with a 16MHz clock) the output of the window
comparator is updated. In a worst-case scenario, it takes six clock cycles for the window comparator to detect
a current limit. The window comparators need a continuous clock to operate properly.
In motor control applications, the window comparators are used to monitor the main currents for failures.