KA3842B/KA3843B/KA3844B/KA3845B
Figure 5. Oscillator Waveforms and Maximum Duty Cycle
Oscillator timing capacitor, C , is charged by V
through R , and discharged by an internal current source. During the dis-
T
T
REF
charge time, the internal clock signal blanks the output to the low state. Selection of R and C therefore determines both
T
T
oscillator frequency and maximum duty cycle. Charge and discharge times are determined by the formulas:
t = 0.55 R C
c
T
T
0.0063RT – 2.7
---------------------------------------
0.0063RT – 4
tD= RTCTIn
Frequency, then, is: f=(t + t )-1
c
d
1.8
ForRT > 5KΩ,f= --------------
RTCT
Figure 6. Oscillator Dead Time & Frequency
(Deadtime vs C RT > 5kΩ)
Figure 7. Timing Resistance vs Frequency
T
Figure 8. Shutdown Techniques
6
FAIRCHILD [ FAIRCHILD SEMICONDUCTOR ]
