ADCMP370/ADCMP371

Preliminary Technical Data

Rev. PrB | Page 6 of 8

APPLICATIONS INFORMATION

BASIC COMPARATOR

In it’s most basic configuration, a comparator can be used to

convert an analog input signal to a digital output signal. The

analog signal on IN+ is compared to the voltage on IN- and the

voltage at OUT is either high or low depending on whether IN+

is at a higher or lower potential than IN-, respectively.

The ADCMP370 and ADCMP371 have different digital output

structures. The ADCMP370 has an open-drain output stage

which requires an external resistor to pull OUT to the logic

high voltage level when the output transistor is switched off.

This voltage level can be as high as 22V. The pull-up resistor

should be large enough to avoid excessive power dissipation, but

small enough to switch logic levels reasonably quickly when the

comparator output is connected to other digital circuitry. A

suitable value would be between 1k

ADCMP371 has a push-pull output stage which has an internal

PMOS pull-up and therefore doesn’t require an external resistor.

Faster switching speeds between low and high rails are possible,

ADM331

OUT

t

0V

Figure 12. Basic Comparator and Input and Output Signals

ADDING HYSTERESIS

To prevent oscillations at the output caused by noise or slowly

moving signals passing the switching threshold, positive

feedback can be used to add hysteresis to the differential input.

For the non-inverting configuration, shown in figure 13, 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 is increasing,

The upper input threshold level is given by:

()

2

1

2

1

V

V

REF

IN_HI

R

R

V

R

R

CC

−

+

=

The lower input threshold level is given by:

()

2

2

1

V

V

REF

IN_LO

R

R

R

+

=

The hysteresis is the difference between these voltage levels:

2

1

V

V

CC

IN

R

R

=

∆

In the example in figure 13, resistors R1 and R2 are chosen to

R1=200k

ADM331

OUT

RLOAD

VIN

IN-

IN+

VIN

VOUT

VREF=2.5V

R2=1M

=2V

=3V

Figure 13. Non-Inverting Comparator Configuration with Hysteresis

ADCMP370

ADCMP370