Datasheet

LTC1443/LTC1444/LTC1445
9
144345fe
applicaTions inForMaTion
Bypassing the reference can help prevent false tripping of
the comparators by preventing glitches on the V
+
or the
reference output voltage. Figure 3 shows the bypassed
reference output with a square wave applied to the V
+
pin.
Resistors R1 and R2 set 10mV of hysteresis, while R3
damps the reference response. Note that the comparator
output doesn’t trip.
Hysteresis
Hysteresis can be added to the LTC1444/LTC1445 by con-
necting a resistor (R1) between the REF and HYST pins,
and a second resistor (R2) from HYST to V
–
(Figure 4).
The difference between the upper and lower threshold volt-
ages or hysteresis voltage band (V
HB
) is equal to twice the
voltage difference between the REF and HYST pins. When
more hysteresis is added, the upper threshold increases
the same amount as the lower threshold decreases. The
maximum voltage allowed between REF and HYST is
50mV, producing a maximum hysteresis voltage band of
100mV. If hysteresis is not wanted, the HYST pin should
be shorted to REF. Acceptable values for I
REF
range from
0.1µA to 5µA. If 2.4M is chosen for R2, then R1(kΩ) =
V
HB
(mV).
IN A
+
5
OUT
V
+
R1
10k
R3
430Ω
R2
2.4M
C1
1.0µF
IN A
–
HYST
REF
4
14
8
5V
TO 8V
144345 F03a
LTC1445
3
9
2
–
+
1.2V
+
–
V
–
Figure 3a. V
+
Glitching Test Circuit
Figure 3b. V
+
Glitching Response
Figure 4. Programmable Hysteresis
8
R2
HYST
REF
14
R1
144345 F04
LTC1445
9
I
REF
R1 =
V
HB
(2)(I
REF
)
R2 =
I
REF
V
HB
2
( )
1.221V –
V
+
8V
5V
V
REF
144345 F03b
OUT
2ms/DIV
2mV/DIV