Separate Supply Voltage Pins for Isolation of
Frequency Control Inputs and Oscillators
from Output Circuitry

Highly Stable Operation over Specified
Temperature and/or Supply Voltage Ranges

description
‘These voltage-controlled oscillators (VCOs) are improved versions of the original VCO family: SNS4LS124, SN64LS324
thru SN54LS327, SN74L5124, and SNT4LS324 thru SN74LS327. These new devices feature improved voltage-to-
frequency linearity, range, and compensation. With the exception of the 'LS624 and 'LS628, all of thess devices feature
two independent VCOs in a single monolithic chip. The ‘L624, 'LS625, 'LS626, and 'LS628 have complementary
Z outputs. The output frequency for each VCO is established by a single external component (either a capacitor or
crystal) in combination with voltage-sensitive inputs used for frequency control and frequency range. Each device
has a voltage-sensitive input for frequency control; however, the 'LS624, "LS628, and "L562 devices also have one
for frequency range. (See Figures 1 thru 6).
The 'LS628 offers more precise temperature compensation than its 'LS624 counterpart, The 'LS624 features a 600 ohm
internal timing resistor. The 'LS628 requires a timing resistor to be connected externally across Rext pins. Temperature
compensation will be improved dur to the temperature coefficient of the external resistor.
Figure 3 and Figure 6 contain the necessary information to choose the proper capacitor value to obtain the desired
operating frequency.
A single 5-volt supply can be used: however, one set of supply voltage and ground pins (VCC and GND) is provided
for the enable, synchronization-gating, and output sections, and a separate set (SC VCC and OSC GND) is provided
for the oscillator and associated frequency-control circuits so that effective isolation can be accomplished in the system.
For operation of frequencies greater than 10 MH, it is recommended that two independent supplies be used. Disabling
either VCO of the 'LS625 and "LS625 and 'LS627 can be achieved by removing the appropriate OSC VCC. An enable
input is provided on the 'LS624, "LS626, 'LS628, and 'LS629. When the enable input is low, the output is enabled:
‘when the enable input is high, the internal oscillator is disabled, Y is high. and Z is low. Caution! Crosstalk may occur
in the dual devices ('LS625, 'LS626, 'LS627 and 'LS629) when both VCOs are operated simultaneously. To minimize
crosstalk, either of the following are recommended: (A) If frequencies are widsly separated, se a 10-uh inductor
between VCC pins. (B) If frequencies are closely spaced, use two separate VGC supplies or place two series diodes
between the Vc pins.
‘The pulse-synchronization-gating section ensures that the first output pulse is neither clipped nor extended. The duty
cycle of the square-wave output is fixed at approximately 50 percent.
‘The SN54LS624 thru SNS4LS629 are characterized for operation over the full military temperature range of — 55°C
to 125°C. The SN74LS624 thru SN74LS629 are characterized for operation from 0°C to 70°C.