maximum difference between REF and HYST (50mV)

will therefore produce a 100mV max hysteresis band.

Use the following equations to determine R1 and R2:

should not exceed the REF source capability, and

should be significantly larger than the HYST input

usually appropriate. If 2.4M

Ω is chosen for

approximated as:

When hysteresis is obtained in this manner for

the MAX932/MAX933, the same hysteresis applies to

both comparators.

Hysteresis (MAX934)

Hysteresis can be set with two resistors using positive

feedback, as shown in Figure 4. This circuit generally

draws more current than the circuits using the HYST

pin on the MAX931/MAX932/MAX933, and the high

feedback impedance slows hysteresis. The design

procedure is as follows:

1. Choose R3. The leakage current of IN+ is under 1nA

(up to +85°C), so the current through R3 can be

around 100nA and still maintain good accuracy.

or 100nA for R3 = 11.8M

Ω. 10MΩ is a good

practical value.

between the upper and lower thresholds. In this

3. Calculate R1.

5. Calculate R2.

A 1% preferred value is 64.9k

Ω.

6. Verify the threshold voltages with these formulas:

V

rising :

V

V

R1

1

R1

1

R2

1

R3

V

falling :

V

V

R1

V

R3

IN

THR

REF

IN

THF

THR

=×

×

+

+









=−

×+

()

R2 =

V

(V

1

R1

1

R3

3

(1.182

100k)

1

100k

1

10M

65.44k

THR

REF

R1)

1

1

×











 −−

















=

×









−−

















=

Ω

R1 = R3

V

V

10M

0.05

5

100k

HB

×

+

=×

=Ω

R1 (k ) = V

(mV)

HB

Ω

R1 =

V

2

I

R2 =

1.182 –

V

2

I

HB

REF

HB

REF

×

()









Ultra Low-Power, Low-Cost

Comparators with 2% Reference

10

______________________________________________________________________________________

GND

V-

V+

MAX934

OUT

R3

R1

R2

V+

Figure 4. External Hysteresis

7

2

5

6

HYST

REF

V-

V+

R1

R2

MAX931

MAX932

MAX933

2.5V TO 11V

Figure 3. Programming the HYST Pin