Datasheet

V
OUT
TIME
V
IN
HYSTERESIS
(DEAD) BAND
POSITIVE
TRIP POINTS
NEGATIVE
TRIP POINTS
V
OUT
V
IH
V
TH
V
IL
V
+
V
HYSTP
V
HYSTN
GND
EXAMPLE 1
EXAMPLE 2
V
IN
V
OUT
V
IH
0
1
V
REF
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
hysteresis in the final circuit. This is most easily accomplished in the breadboard phase by making R
1
and R
2
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.
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