LM393, LM393A, LM293, LM2903, LM2903V

5

MOTOROLA ANALOG IC DEVICE DATA

APPLICATIONS INFORMATION

These dual comparators feature high gain, wide

bandwidth characteristics. This gives the device oscillation

tendencies if the outputs are capacitively coupled to the

inputs via stray capacitance. This oscillation manifests itself

during output transitions (VOL to VOH). To alleviate this

situation, input resistors < 10 k

Ω should be used.

The addition of positive feedback (< 10 mV) is also

recommended. It is good design practice to ground all

unused pins.

Differential input voltages may be larger than supply

voltage without damaging the comparator’s inputs. Voltages

more negative than –0.3 V should not be used.

Figure 7. Zero Crossing Detector

(Single Supply)

Figure 8. Zero Crossing Detector

(Split Supply)

Figure 9. Free–Running Square–Wave Oscillator

Figure 10. Time Delay Generator

Figure 11. Comparator with Hysteresis

10

D1 prevents input from going negative by more than 0.6 V.

R1 + R2 = R3

R3

≤

R5

for small error in zero crossing.

Vin

10 k

D1

R1

8.2 k

6.8 k

R2

15 k

R3

+15 V

10 M

R5

220 k

R4

220 k

LM393

Vin(min) [ 0.4 V peak for 1% phase distortion (∆Θ).

*

Θ

+VCC

10 k

Vin

–VEE

Vin

Vin(min)

VCC

VO

– VEE

∆Θ

Θ

LM393

–

+

LM393

51 k

51 k

51 k

RL

10 k

VCC

VCC

VCC

VO

VO

t

0

1.0 M

Ω

0.001

µF

–

+

LM393

VCC

VCC

VO

Vin

VO

+ Vref

Vref

Vref

0

0

0

VC

tO

t

‘‘ON’’ for t

­ tO + ∆t

where:

∆t = RC n (

Vref

VCC

)

R

RL

VC

C

LM393

–

+

RS

VCC

RL

Vref

R1

R2

RS = R1 | | R2

Vth1 = Vref +

(VCC –Vref) R1

R1 + R2 + RL

Vth2 = Vref –

(Vref –VO Low) R1

R1 + R2

R1

t

–

+

LM393

)

*

)