LTC1440 datasheet(12/16 Pages) LINER

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LTC1440/LTC1441/LTC1442

144012fd

APPLICATIONS INFORMATION

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(k

Ω) = VHB = 15k

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

REF

BIAS

REF

1 182

118

−

⎡

⎣

⎢

⎤

⎦

⎥

21 18

465

1 182

23 40

−

⎡

⎣

⎢

⎤

⎦

⎥

Low Voltage Operation

It is important to note that the voltage references internal

to the LTC1440 and LTC1442 can exceed the common

mode range of the comparators at low supply voltages.

The input common mode range of the LTC1440/LTC1441/

LTC1442 comparators is guaranteed to extend up to (V+ -

1.3V). Therefore, if one of the comparator inputs is at the

1.182V reference voltage, the minimum supply voltage is

2.5V for a valid output reading.

The guaranteed minimum operating voltage for the

LTC1440/LTC1441/LTC1442 is 2V (or

±1V). However,

both the reference and comparator(s) will function with a

supply voltage as low as 1.5V, but performance will

degrade as the voltage goes below 2V. The voltage refer-

ence temperature coefficient will degrade slightly, and the

comparators will have less output drive with an increase in

propagation delay. At the reduced supply voltages, the

input common mode range of the comparator(s) will still

typically extend from the negative supply to approximately

1.1V below the positive supply.

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