8

LTC1841/LTC1842/LTC1843

Figure 3a. Power Supply Transient Test Circuit

8V

5V

OUT

2ms/DIV

1841/1843 F03b

Figure 3b. Power Supply Transient Rejection

Hysteresis

Hysteresis can be added to the LTC1842/LTC1843 by

connecting a resistor (R1) between the REF and HYST pins

The difference between the upper and lower threshold

the voltage difference between the REF and HYST pins.

As more hysteresis is added, the upper threshold in-

creases the same amount as the low threshold decreases.

The maximum voltage allowed between REF and HYST

pins is 50mV, producing a maximum hysteresis voltage

band of 100mV. The hysteresis band may vary by up to

Figure 4. Programmable Hysteresis

15%. If hysteresis is not wanted, the HYST pin should be

0.1

µA to 5µA. If 2.4M is chosen for R2, then the value of

Window Detector

The LTC1843 is ideal for use as a micropower window

detector as shown in Figure 5. The values of R1, R2 and R3

are selected for a 4.5V undervoltage threshold and a 5.5V

overvoltage threshold. R4 and R5 set the hysteresis volt-

age. The following design procedure can be used to select

the component values:

–

+

–

+

R4

2.4M

R1

294k

R2

62.2k

R3

1M

1M

R5

10k

HYST

3

5V

5

LTC1843

2

4

OUT B

1841/43 F05

8

OUT A 1

7

REF

6

Figure 5. Dual Level Detector

6

R2

5

R1

1841/43 F04

2

R1 =

R2 =

1.182V –

()

2

HYST

REF

LTC1843

R1

430

Ω

R2

10k

C1

1

µF

5V

TO

8V

OUT A

OUT A

2

7

5V

1

LTC1843

1841/43 F03a

HYST

REF

3

5

6

1M

R3

2.4M

–

+