TIME

HYSTERESIS

(DEAD) BAND

POSITIVE

TRIP POINTS

NEGATIVE

TRIP POINTS

V

+

GND

EXAMPLE 1

EXAMPLE 2

0

1

OUTPUT

STATE

LMP7300

www.ti.com

SNOSAT7F – AUGUST 2007 – REVISED MARCH 2013

Figure 22. Connections for Positive Hysteresis = +10 mV

In the general case, as demonstrated with both positive and negative hysteresis bands in Figure 23, noise within

these bands will have no affect on the state of the comparator output. In Example #1 the noise is well behaved

and in band. The output is clean and well behaved. In Example #2, a significant amount of out of band noise is

present but due to hysteresis no false triggers occur on the rising positive or falling negative edges. The

hysteresis forces the signal level to move higher or lower before the output is set to the opposite state.

Figure 23. Output Response with Input Noise Less than Hysteresis Band

How Much Hysteresis Is Correct?

An effective way of determining the minimum hysteresis necessary for clean switching is to decrease the amount

of hysteresis until false triggering is observed, and then use a multiple of say three times that amount of

potentiometers. For applications near or above +100°C a minimum of 5 mV hysteresis is recommended due to

peaking of the LMP7300 noise sensitivity at high temperatures.

LAYOUT RECOMMENDATIONS

A good PCB layout is always important to reduce output to input coupling. Positive feedback noise reduces

performance. For the LMP7300 output coupling is minimized by the unique package pinout. The output is kept

away from the non-inverting and inverting inputs, the reference and the hysteresis pins.

Copyright © 2007–2013, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: LMP7300