AS1970 데이터 시트보기 (PDF) - austriamicrosystems AG

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AS1970

Low-Voltage Single/Dual/Quad Comparators

austriamicrosystems AG 

AS1970

Data Sheet - Application Information

9 Application Information

Figure 17 shows a typical application circuit for the AS1970 - AS1975 comparators.

Figure 17. Typical Application Diagram – Threshold Detector

VIN

2

4

VCC

IN-

AS1970 - AS1975

1

OUT

RPULLUP †

3

5

IN+

VEE

† AS1971/AS1973/AS1975 only

Hysteresis (AS1970/AS1972/AS1974)

The AS1970/AS1972/AS1974 have 3mV internal hysteresis. Additional hysteresis can be generated with three resis-

tors using positive feedback (Figure 18), however this method also slows hysteresis response time.

Figure 18. Additional Hysteresis AS1970/AS1972/AS1974

VCC

R3

R1

VIN

R2

+ VCC

VEE

–

VREF

OUT

Resistor Selection Example

For the circuit shown in Figure 18, the following steps can be used to calculate values for R1, R2, and R3.

1. Select R3 first. The current through R3 should be at least 1µA to minimize errors caused by leakage current. The

current through R3 at the trip point is:

(VREF - VOUT)/R3

The two possible output states in solving for R3 yields these two formulas:

(EQ 1)

R3 = VREF/1µA

(EQ 2)

R3 = (VREF - VCC)/1µA

(EQ 3)

For example, for VREF = 1.2V and VCC = 5V, the two R3 resistor values are 1.2MΩ and 3.8MΩ. Use the smaller of

the two resulting resistor values; in this case a standard 1.2MΩ resistor should be used for R3.

2. Choose the hysteresis band (VHB). For this example, use VHB = 50mV.

3. Calculate R1 according to the following equation:

R1 = R3(VHB/VCC)

Substituting the example values for R3 and VHB gives:

(EQ 4)

R1 = 1.2MΩ(50mV/5V) = 12kΩ

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