KA3524
4
Application Information
Voltage Reference
An internal series regulator provides a nominal 5 volt output which is used both to generate a reference voltage and is
the regulated source for all the internal timing and controlling circuitry. This regulator may be bypassed for operation
from a fixed 5 volt supply by connecting pins 15 and 16 together to the input voltage. In this configuration, the maximum
input voltage is 6.0 volts.
This reference regulator may be used as a 5 volt source for other circuitry. It will provide up to 50mA of current itself
and can easily be expanded to higher current with an external PNP as shown in Figure 2.
Expanded Reference Current Capability
Oscillator
The oscillator in the KA3524 uses an external resistor (R
T
) to establish a constant charging current into an external capacitor
(C
T
), While this uses more current than a series connected PC, it provides a linear ramp voltage on the capacitor which is also
used as a reference for the comparator. The charging current is equal to 3.6V/R
T
and should be kept within the range of
approximately 30uA to 2mA, i.e., 1.8K< R
T
<100K. The range of values for C
T
also has limits as the discharge time of C
t
determines the pulse width of the oscillator output pulse. This pulse is used (among other things) as a blanking pulse to both
outputs to insure that there is no possibility of having both outputs on simultaneously during transitions. This output dead time
relationship is shown in Figures. A pulse width below approximately 0.5 microseconds may allow false triggering of one out-
put by removing he blanking pulse prior to the flip-flops reaching a stable state. If small values of C
T
must be used, the pulse
width may still be expanded by adding a shunt capacitance (= 100pF) to ground at the oscillator output. (Note: Although the
oscillator output is a convenient oscilloscope sync input, the cable and input capacitance may increase the blanking pulse
width slightly.) Obviously, the upper limit of the pulse width is determined by the maximum duty cycle acceptable. Practical
values of C
T
fall between 0.01 and0.1 micro farad. The oscillator period is approximately t = R
T
C
T
where t is in microsec-
onds when R
T
ohms and C
T
= micro farads. The selection of R
T
and C
T
can be made for a wide range of operating frequen-
cies by using Fig. 7. Note that for sense regulator applications, the two outputs can be connected in parallel for an effective 0-
90% duty cycle and the frequency of the oscillator is the frequency of the output. For push-pull applications, the outputs are
separated and the flip-flop divides the frequency such that each output duty cycle is 0-45% and the overall frequency is one-
half that of the oscillator.
External Synchronization
If It is desired to synchronize the KA3524 to an external clock, a pulse of +3 volts may be applied to the oscillator output
terminal with R
T
C
T
set slightly greater than the clock period. The same considerations of pulse width apply. The impedance to
ground at this point is approximately 2K ohms. If two or more KA3524s must be synchronized together, one must be desig-
nated as the master with its R
T
C
T
set for the correct period. The slaves should each have an R
T
C
T
set for an approximately
10% longer period than the master with the added requirement that C
T
(slave) = one-half C
T
(master). Then connecting Pin 3
on all units together will insure that the master output pulse-which occurs first and has a wider pulse width - will reset the
slave units.
