LMV7219

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SNOS458G – APRIL 2000 – REVISED JANUARY 2015

8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

The following section explains in detail how to manipulate the hysteresis voltage of the LMV7219. Detailed

expressions are provided along with practical considerations for designing hysteresis.

8.2 Typical Application

Figure 14 shows the typical method of adding external hysteresis to a comparator. The positive feedback is

responsible for shifting the comparator trip point depending on the state of the output.

Figure 14. Additional Hysteresis

8.2.1 Design Requirements

The internal hysteresis creates two trip points, one for the rising input voltage and one for the falling input

voltage, as shown in Figure 19. The difference between the trip points is the hysteresis. With internal hysteresis,

when the comparator's input voltages are equal, the hysteresis effectively causes one comparator-input voltage

to move quickly past the other, thus taking the input out of the region where oscillation occurs. Standard

comparators require hysteresis to be added with external resistors. The fixed internal hysteresis eliminates these

resistors.

8.2.2 Detailed Design Procedure

8.2.2.1 Additional Hysteresis

If additional hysteresis is desired, this can be done with the addition of three resistors using positive feedback, as

shown in Figure 14. The positive feedback method slows the comparator response time. Calculate the resistor

values as follows:

1. Select R3. The current through R3 should be greater than the input bias current to minimize errors. The

for R3, and use the smaller of the two resulting resistor values. The two formulas are:

(1)

(2)

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