MAX934CSE データシートの表示（PDF） - Maxim Integrated

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MAX934CSE

Ultra Low-Power, Low-Cost Comparators with 2% Reference

Maxim Integrated 

Ultra Low-Power, Low-Cost

Comparators with 2% Reference

maximum difference between REF and HYST (50mV)

will therefore produce a 100mV max hysteresis band.

Use the following equations to determine R1 and R2:

R1 =

VHB

(2 × IREF )

R2 =

1.182 –

VHB

2





IREF

Where IREF (the current sourced by the reference)

should not exceed the REF source capability, and

should be significantly larger than the HYST input

current. IREF values between 0.1µA and 4µA are

usually appropriate. If 2.4MΩ is chosen for

R2 (IREF = 0.5µA), the equation for R1 and VHB can be

approximated as:

R1 (kΩ) = VHB (mV)

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.

The current through R3 at the trip point is VREF/R3,

or 100nA for R3 = 11.8MΩ. 10MΩ is a good

practical value.

2. Choose the hysteresis voltage (VHB), the voltage

between the upper and lower thresholds. In this

example, choose VHB = 50mV.

3. Calculate R1.

R1 = R3 × VHB

V+

= 10M × 0.05

5

= 100kΩ

4. Choose the threshold voltage for VIN rising (VTHR). In

this example, choose VTHR = 3V.

5. Calculate R2.

R2 =

1





VTHR

(VREF × R1)







−

1

R1

−

1

R3







=

1



 (1.182

3

×



100k)

−

1

100k

−

1

10M





= 65.44kΩ

A 1% preferred value is 64.9kΩ.

6. Verify the threshold voltages with these formulas:

VIN rising :

VTHR

= VREF

×

R1

×

1

 R1

+

1

R2

+

1

R3 

VIN falling :

(R1 × V +)

VTHF = VTHR −

R3

2.5V TO 11V

7

IREF

6

REF

V+

R1

MAX931

MAX932

5 MAX933

HYST

R2

V-

2

V+ R3

R1

VIN

R2

V+ OUT

MAX934 V-

GND

VREF

Figure 3. Programming the HYST Pin

Figure 4. External Hysteresis

10 ______________________________________________________________________________________

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