LTC1445CS datasheet(9/14 Pages) LINER

9 / 14 page

LTC1443/LTC1444/LTC1445

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).

Thedifferencebetweentheupperandlowerthresholdvolt-

ages or hysteresis voltage band (VHB) 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 IREF range from

0.1µA to 5µA. If 2.4M is chosen for R2, then R1(kΩ) =

VHB (mV).

IN A+

OUT

V+

10k

430

2.4M

1.0µF

IN A–

HYST

REF

TO 8V

144345 F03a

LTC1445

–

1.2V

+–

V–

Figure 3a. V+ Glitching Test Circuit

Figure 3b. V+ Glitching Response

Figure 4. Programmable Hysteresis

HYST

REF

144345 F04

LTC1445

IREF

R1 =

VHB

(2)(IREF)

R2 =

IREF

VHB

(

)

1.221V –

V+

VREF

144345 F03b

OUT

2ms/DIV

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