Data Sheet

TYPICAL APPLICATIONS

To add hysteresis, see Figure 23; two resistors are used to create
different switching thresholds, depending on whether the input
signal is increasing or decreasing in magnitude. When the input
voltage increases, the threshold is above V

REF

, and when the

input voltage decreases, the threshold is below V

REF

Figure 23. Noninverting Comparator Configuration with Hysteresis

The upper input threshold level is given by

R2

R2

R1

V

V

REF

IN_HI

)

( +

=

(2)

Assuming R

>> R2, R

PULLUP

.

The lower input threshold level is given by

(

)

PULLUP

CC

PULLUP

REF

LO

IN

R

R2

R1

V

R

R2

R1

V

V

+

+

+

=

_

(3)

The hysteresis is the difference between these voltages levels.

PULLUP

CC

IN

R

R2

R1

V

ΔV

+

=

(4)

WINDOW COMPARATOR FOR POSITIVE VOLTAGE

MONITORING

When monitoring a positive supply, the desired nominal
operating voltage for monitoring is denoted by V

M

, I

M

is the

nominal current through the resistor divider, V

OV

is the

overvoltage trip point, and V

UV

is the undervoltage trip point.

Figure 24. Positive Undervoltage/Overvoltage Monitoring Configuration

Figure 24 illustrates the positive voltage monitoring input
connection. Three external resistors, R

X

, R

Y

, and R

Z

, divide the

positive voltage for monitoring, V

M

, into the high-side voltage,

V

PH

, and the low-side voltage, V

PL

. The high-side voltage is

connected to the INA+ pin and the low-side voltage is
connected to the INB− pin.
To trigger an overvoltage condition, the low-side voltage (in this
case, V

PL

) must exceed the V

REF

threshold on the INB+ pin.

Calculate the low-side voltage, V

PL

, by the following:





+

+

=

=

Z

Y

X

Z

OV

REF

PL

R

R

R

R

V

V

V

(5)

R

X

+ R

Y

+ R

Z

= V

M

/I

M

(6)

Therefore, R

Z

, which sets the desired trip point for the

overvoltage monitor, is calculated as

(

)

( )

( )

( )

M

OV

M

REF

Z

I

V

V

V

=

(7)

To trigger the undervoltage condition, the high-side voltage,
V

PH

, must be less than the V

REF

threshold on the INA− pin. The

high-side voltage, V

PH

, is calculated by





+

+

+

=

=

Z

Y

X

Z

Y

UV

REF

PH

R

R

R

R

R

V

V

V

(8)

Because R

Z

Y

can be expressed as

(

)

( )

( )

( )

Z

M

UV

M

REF

Y

R

I

V

V

V

R

=

(9)

When R

Y

and R

Z

are known, R

X

can be calculated by

R

X

= (V

M

/I

M

) – R

Y

− R

Z

(10)

If V

M

, I

M

, V

OV

, or V

UV

changes, each step must be recalculated.

OUT

INx+

INx–

V

REF

= 2.5V

V

IN

V

CC

= 5V

R1

R

R

PULLUP

R2

V

OUT

V

IN

V

IN_LO

V

IN_HI

12207-

030

V

REF

V

M

R

Z

R

Y

R

X

V

PL

V

PH

OUTA

INA+

INA–

OUTB

INB+

INB–

12207-

021

Rev. 0 | Page 10 of 15

Part No.

Description