AS1971 datasheet(13/19 Pages) AMSCO

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AS1970

Data Sheet - Ap p lica tio n In fo r m a tio n

Hysteresis Band

Internal hysteresis creates two trip points (shown in Figure 20): rising input voltage (VTHR) and falling input voltage

(VTHF). The area between the trip points is the hysteresis band (VHB). When the comparator input voltages are equiva-

lent, the hysteresis effectively causes one comparator input to move quickly past the other, thus taking the input out of

the region where oscillation occurs.

In Figure 20 REF has a fixed voltage applied and IN+ is varied. If the inputs are reversed the output will be inverted.

Figure 20. Threshold Hysteresis Band

Zero-Crossing Detector

Figure 21 shows the AS1970 in a zero-crossing detector circuit. The inverting input is connected to ground, and the

non-inverting input is connected to a 100mVp-p signal source. As the signal at the non-inverting input crosses 0V, the

signal at OUT changes states.

Figure 21. Zero-Crossing Detector

Logic Level Translator

The comparators can be used as a 5V/3V logic translator as shown in Figure 22. The circuit in Figure 22 converts 5V-

to 3V-logic levels, and provides the full 5V logic-swing without creating overvoltage on the 3V logic inputs. When the

comparator is powered by a 5V supply, RPULLUP for the open-drain output should be connected to the +3V supply volt-

age.

For 3V-to-5V logic-level translations, connect the +3V supply voltage to VCC and the +5V supply voltage to RPULLUP.

Figure 22. Logic Level Translator

IN+

OUT

VTHR

VTHF

REF

Thresholds

Hysteresis

Band

VHB

VEE

OUT

100mVp-p

AS1970

IN-

IN+

VCC

–

AS1971

RPullup

+5/+3V

Logic Out

+3/+5V

+5/+3V

Logic In

100k

+3/+5V

IN-

VEE

IN+

OUT

VCC

–

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