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