7

LTC1540

sn1540 1540fas

Hysteresis

Hysteresis can be added to the LTC1540 by connecting a

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

The difference between the upper and lower threshold

the voltage difference between the REF and HYST pins.

When more hysteresis is added, the upper threshold

increases the same amount as the low threshold de-

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

from 0.1µA to 5µA. If 2.4M is chosen for R2, then the value

6

R2

HYST

REF

5

R1

1540 • F05

LTC1540

2

R1 =

R2 =

1.182V –

()

2

Figure 5. Programmable Hysteresis

Figure 6. Glitch-Free Level Detector with Hysteresis

Level Detector

The LTC1540 is ideal for use as a nanopower level detector

as shown in Figure 6. R1 and R2 form a voltage divider

set the hysteresis voltage, and R5 and C1 bypass the

reference output. The following design procedure can be

used to select the component values:

2. Calculate the required resistive divider ratio.

Ratio = 1.182V/4.65V = 0.254

3. Choose the required hysteresis voltage band at the

4. Choose the values for R3 and R4 to set the hysteresis.

R4 = 2.4M

5. Choose the values for R1 and R2 to set the trip point.

R1 =

R2 = R1

– 1

=

= 1.18M

2

1.182V

1µA

R2 = 1.18M

R2 = 3.40M

– 1

1.182V +

4.65V

15mV

2

R5

430Ω

5%

R3

15k

1%

C1

1µF

OUT

21

7

5V

8

GND

LTC1540

1540 F06

HYST

REF

3

4

5

6

–

+

R2

3.4M

1%

R1

1.18M

1%

R4

2.4M

1%