LM393 Просмотр технического описания (PDF) - Unspecified

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LM393

36V Low Power Dual/Quad Differential Comparators

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LM393/LM339

36V Low Power Dual/Quad Differential Comparators

VA2



VDD  R 2 || R 3

R 1  R 2 || R 3

If R1=R2=R3, then VA1=2VDD /3, and VA2= VDD/3

The capacitor C1 now discharges through R4, and the voltage VC decreases till it is equal to VA2, at which point the

comparator switches again, bringing it back to the initial stage. The time period is equal to twice the time it takes to

discharge C1 from 2VDD/3 to VDD/3. Hence the frequency is:

1

Freq 

2  ln2  R 4  C1

VDD

R1

VA

VC1

R2

C1

R3

LM393

R4

VO

t

Vo

VC1

2/3VDD

1/3VDD

t

R1=R2=R3

Figure 7. Relaxation Oscillator

Windowed Comparator

Figure 8 shows one approach to designing a windowed comparator using a single LM393/339 chip. Choose different

thresholds by changing the values of R1, R2, and R3. OutA provides an active-low undervoltage indication, and OutB

gives an active-low overvoltage indication. ANDing the two outputs provides an active-high, power-good signal. When

input voltage Vi reaches the overvoltage threshold VOH, the OutB gets low. Once Vi falls to the undervoltage threshold

VUH, the OutA gets low. When VUH<Vi<VOH, the AND Gate gets high.

VOH  Vr  (R1  R 2  R3 )/R1

VUH  Vr  (R1  R 2  R3 )/(R1  R 2 )

Figure 8. Windowed Comparator

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Rev. B.2

10

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