Features, Applications The LM and LMC are general purpose phase locked loops containing a stable, highly linear voltage controlled oscillator for low distortion FM demodulation, and a double balanced phase detector with good carrier suppression. The VCO frequency is set with an external resistor and capacitor, and a tuning range of can be obtained with the same capacitor. The characteristics of the closed loop system bandwidth, response speed, capture and pull in range may be adjusted over a wide range with an external resistor and capacitor. The loop may be broken between the VCO and the phase detector for insertion of a digital frequency divider to obtain frequency multiplication. Operating Ratings indicate conditions for which the device is functional, but do not guarantee specific performance limits. Electrical Characteristics state DC and AC electrical specifications under particular test conditions which guarantee specific performance limits.
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The device being cheap can be used in applications where cost is considered. In order to understand let us simplify this block diagram further to get the following. In the device pin 2 and pin3 are inputs where we can connect the input analog signal but usually pin 3 will be grounded and pin2 is used as input. The input signal goes in to the phase detector along with VCO feedback and this phase detector compares whether both signal are in same phase or frequency.
If they are in phase or frequency the PD provides zero voltage output and if phase or frequency is present the PD provides positive output voltage. This output voltage of PD is given to amplifier to amplify the voltage signal and the amplified voltage is given to VCO, which generates waveform whose frequency depends on magnitude of the given input voltage.
Now consider no input is given, under such case the VCO will be in free running mode generating signal whose frequency is determined by the capacitor and resistor connected at the pin 8 and pin 9. When a signal is given at the input, the frequency of both input signal and the VCO output is compared.
The VCO will increase or decrease the signal frequency depending of the fed voltage of amplifier. Once the adjustment is done both the input signal frequency and VCO frequency will match. This is how a phase locked loop works, the VCO output signal frequency will always tries to keep up with the input signal frequency.
LM565CN National Semiconductor, LM565CN Datasheet