LTC1540CS8 datasheet(7/12 Pages) LINER

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LTC1540

sn1540 1540fas

APPLICATIONS INFORMATION

Hysteresis

Hysteresis can be added to the LTC1540 by connecting a

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

second resistor (R2) from HYST to V – (Figure 5).

The difference between the upper and lower threshold

voltages, 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 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

should be shorted to REF. Acceptable values for IREF range

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

of R1 (kΩ) is equal to the value of VHB (mV).

HYST

V–

REF

1540 • F05

LTC1540

IREF

R1 =

VHB

(2)(IREF)

R2 =

IREF

1.182V –

()

VHB

Figure 5. Programmable Hysteresis

Figure 6. Glitch-Free Level Detector with Hysteresis

TYPICAL APPLICATIONS

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

from VIN to the noninverting comparator input. R3 and R4

set the hysteresis voltage, and R5 and C1 bypass the

reference output. The following design procedure can be

used to select the component values:

1. Choose the VIN voltage trip level, in this example 4.65V.

2. Calculate the required resistive divider ratio.

Ratio = VREF/VIN

Ratio = 1.182V/4.65V = 0.254

3. Choose the required hysteresis voltage band at the

input VHBIN, in this example 60mV. Calculate the hyster-

esis voltage band referred to the comparator input VHB.

VHB = (VHBIN)(Ratio)

VHB = (60mV)(0.254)

VHB = 15.24mV

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

R4 = 2.4M

R3 (kΩ) = 15k, VHB (mV) = 15mV

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

R1 =

R2 = R1

– 1

= 1.18M

VREF

IBIAS

VREF +

VIN

VHB

1.182V

1µA

R2 = 1.18M

R2 = 3.40M

– 1

1.182V +

4.65V

15mV

V +

430Ω

15k

1µF

OUT

V –

VIN

GND

LTC1540

1540 F06

IN+

IN–

HYST

REF

–

3.4M

1.18M

2.4M

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