LTC6103 datasheet(22/28 Pages) AD

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LT6119-1/LT6119-2

611912f

For more information www.linear.com/LT6119-1

R1 should be chosen such that R1 >> R6 so that VOUTA

does not change significantly when the comparator

trips.

R3 should be chosen to allow sufficient VOL and compara-

tor output rise time due to capacitive loading.

R2 can be calculated:

R1• V+ – 400mV

(

)– V

HYS(EXTRA) • R3

(

)

VHYS(EXTRA)

For very large values of R2 PCB related leakage may

become an issue. A tee network can be implemented to

reduce the required resistor values.

The approximate total hysteresis will be:

VHYS =10mV+R1•

V+ – 400mV

+R3









For example, to achieve IUNDER = 100µA with 50mV of

total hysteresis, R6 = 3.57k. Choosing R1 = 35.7k, R3 =

10k and V+ = 5V results in R2 = 4.12M.

The analog output voltage will also be affected when the

comparator trips due to the current injected into R6 by

the positive feedback. Because of this, it is desirable to

applicaTions inForMaTion

have (R1 + R2 + R3) >> R6. The maximum VOUTA error

caused by this can be calculated as:

∆VOUTA = V+ •

+R2+R3+R6









In the previous example, this is an error of 4.3mV at the

output of the amplifier or 43µV at the input of the amplifier

assuming a gain of 100.

When using the comparators with their inputs decoupled

fromtheoutputoftheamplifier,theymaybedrivendirectly

by a voltage source. It is useful to know the threshold

voltage equations with the additional hysteresis. The input

fallingedgethresholdwhichcausestheoutputtotransition

from high to low is:

VTH(F) = 400mV •R1•

+R3









–

V+ • R1

+R3









The input rising edge threshold which causes the output

to transition from low to high is:

VTH(R) = 410mV • R1•









Figure 16 shows how to add additional hysteresis to an

inverting comparator.

Figure 16. Inverting Comparator with Added Hysteresis

V+

V–

INC1

V–

611912 F16

OUTA 8

V+

SENSEHI

LT6119-1

RIN

RSENSE

ILOAD

V+

SENSELO

OUTC1

400mV

REFERENCE

R1 VTH

VDD

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