SDLS186 - JANUARY 1980 - REVISED MARCH 1988
PRODUCTION DATA documents contain information current as of publicationdate. Products conform to specifications per the terms of Texas Instrumentsstandard warranty. Production processing does not necessarily include testingof all parameters.
These voltage-controlled oscillators (VCOs) are improved versions of theoriginal VCO family: SN54LS124, SN54LS324 thru SN54LS327, SN74LS124, and SN74LS324thru SN74LS327. These new devices feature improved voltage-to-frequency linearity,range, and compensation. With the exception of the 'LS624 and 'LS628, allof these devices feature two independent VCOs in a single monolithic chip.The 'LS624, 'LS625, 'LS626, and 'LS628 have complementary Z outputs. The outputfrequency for each VCO is established by a single external component (eithera capacitor or crystal) in combination with voltage-sensitive inputs usedfor frequency control and frequency range. Each device has a voltage-sensitiveinput for frequency control; however, the 'LS624, 'LS628, and 'LS629 devicesalso have one for frequency range. (See Figures 1 thru 6).
The 'LS628 offers more precise temperature compensation than its 'LS624counterpart. The 'LS624 features a 600 ohm internal timing resistor. The 'LS628requires a timing resistor to be connected externally across Rextpins. Temperature compensation will be improved due to the temperature coefficientof the external resistor.
Figure 3 and Figure 6 contain the necessary information to choose the propercapacitor value to obtain the desired operating frequency.
A single 5-volt supply can be used: however, one set of supply voltageand ground pins (VCC and GND) is provided for the enable, synchronization-gating,and output sections, and a separate set (OSC VCC and OSC GND) isprovided for the oscillator and associated frequency-control circuits so thateffective isolation can be accomplished in the system. For operation of frequenciesgreater than 10 MHz, it is recommended that two independent supplies be used.Disabling either VCO of the 'LS625 and 'LS625 and 'LS627 can be achieved byremoving the appropriate OSC VCC. An enable input is provided onthe 'LS624, 'LS626, 'LS628, and 'LS629. When the enable input is low, theoutput is enabled: when the enable input is high, the internal oscillatoris disabled, Y is high, and Z is low. Caution! Crosstalk may occur in thedual devices ('LS625, 'LS626, 'LS627 and 'LS629) when both VCOs are operatedsimultaneously. To minimize crosstalk, either of the following are recommended:(A) If frequencies are widely separated, use a 10-μh inductor between VCC pins. (B) If frequencies are closely spaced, use two separate VCC supplies or place two series diodes between the VCC pins.
The pulse-synchronization-gating section ensures that the first outputpulse is neither clipped nor extended. The duty cycle of the square-wave outputis fixed at approximately 50 percent.
The SN54LS624 thru SN54LS629 are characterized for operation over the fullmilitary temperature range of -55°C to 125°C. The SN74LS624 thru SN74LS629are characterized for operation from 0°C to 70°C.
View more information about generic part numbers:SN54LS628, SN54LS629, SN74LS624, SN74LS625, SN74LS626, SN74LS627, SN74LS628, SN74LS629
Go to the Engineering Design Center to locate information on other TI Semiconductor devices.