LTC1444CS datasheet(8/12 Pages) LINER

8 / 12 page

LTC1443/LTC1444/LTC1445

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

connecting 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 (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 maxi-

mum 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(k

Ω) = VHB (mV).

IN A+

OUT

V+

V–

10k

430

Ω

2.4M

1.0

µF

IN A–

HYST

REF

TO 8V

LTC1443/44/45 • F03

LTC1445

–

Figure 3a. V + Glitching Test Circuit

Figure 3b. V + Glitching Response

LTC1443/1444/1445 • TA02

V+

VREF

OUT

2ms/DIV

Figure 4. Programmable Hysteresis

HYST

REF

LTC1443/44/45 • F04

LTC1445

IREF

R1 =

VHB

(2)(IREF)

R2 =

IREF

VHB

()

1.221V –

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