LMV393(2014) Просмотр технического описания (PDF) - Unisonic Technologies
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LMV393 Datasheet PDF : 11 Pages
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LMV393
Preliminary
LINEAR INTEGRATED CIRCUIT
APPLICATION CIRCUITS(Cont.)
Square Wave Oscillator
Comparators are suitable for oscillator applications. This application uses the minimum number of external
components. The output frequency is set by the RC time constant which is determined by capacitor C1 and the
resistor in the negative feedback R4 of the comparator. Capacitive load at the output would degrade the output slew
rate and limit the maximum operating frequency.
V+
C1
75pF
R4
100k
4.3k
V+
-VCC
Va1
Vc1
-
Vc
0
VOUT
Va2
+
R1
R3
V+ 100k Va 100k
t=0
R2
100k
T
VOUT
0
Squarewave Oscillator
At first, assume that the output is high, so the voltage at the inverting input VC is less than the voltage at the
non-inverting input Va, the capacitor C1 has to be discharged. When it has charged up to value equal to the positive
input voltage Va1, the comparator output will switch.
Va1 will be given by:
Va1
=
VCCR2
R2 + (R1/R2
)
If: R1=R2=R3
Then:
Va1
=
2VCC
3
When the output switches to ground, the value of Va is reset by the resistor network:
Va2
=
VCC
3
Then capacitor C1 discharge through a resistor towards ground. The output will return to its high state when the
voltage across the capacitor has discharged to a value equal to Va2.The time to charge the capacitor can be
calculated from:
-t
VC = Vmax eRC
Where VMAX =2VCC/3 and VC = VCC/3
One period will be given by: 1/freq = 2t or calculating the exponential gives: 1/freq = 2(0.694) R4 C1Resistors R3
and R4 must be at least two times larger than R5 to insure a reasonable VO. The frequency stability of this circuit
should strictly be a function of the external components.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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