What is an LM565 IC : Pin Configuration & Its Working

LM565 IC is one of the essential components within linear systems. This IC operates in three modes like free running, capture, and lock mode. Generally, it operates in free-running mode once no input is provided to it. Once an input signal including some frequency is provided to this IC, the voltage-controlled oscillator’s output signal frequency will be changed. At this phase, the phase-locked loop operates within the capture mode.

The voltage-controlled oscillator’s o/p signal frequency changes continuously until it reaches the frequency of the input signal then the PLL operates in the lock mode. This PLL IC is used in communication systems like FMs, satellites, radars, etc. This article discusses an overview of the LM565 phase-locked loop.

What is an LM565 IC?

The LM565 is a general-purpose PLL or phase-locked loop IC which includes a constant, extremely linear VCO (voltage controlled oscillator) for less deformation FM demodulation & a phase detector with double balanced & superior carrier control. The frequency of the voltage-controlled oscillator can be controlled through exterior components like capacitor & resistor.

LM565 Phase Locked Loop IC
LM565 Phase Locked Loop IC

Similarly, the range of tuning like 10:1 can be acquired through a similar capacitor. The closed-loop system characteristics are response speed, BW, capture & pull-in range. This loop may be broken down among the phase detector & VCO due to the inclusion of a digital frequency divider for acquiring frequency multiplication.

Pin Configuration

The pin configuration n of the LM565 Phase Locked Loop IC is shown below. This IC includes 14-pins where each pin and its functionality are discussed below.

LM565 IC Pin Configuration
LM565 IC Pin Configuration
  • Pin1 (-Vcc): Input pin of the negative power supply
  • Pin2 (Input): Input pin1 of the Phase detector
  • Pin3 (Input): Input pin2 of the Phase detector
  • Pin4 (VCO output): Output pin of the voltage-controlled oscillator
  • Pin5 (VCO i/p of Phase comparator): Input pin of the phase detector
  • Pin6 (Reference o/p): Reference o/p of Internal amplifier
  • Pin7 (VCO control voltage): At this pin, the control voltage of VCO can be observed
  • Pin8 (Timing Resistor): Resistor for running the frequency of VCO
  • Pin9 (Timing Capacitor): Capacitor for running the frequency of VCO
  • Pin10 (+Vcc): +Ve power supply
  • Pin11, 12, 13 & 14 : No connection pins

Block Diagram

A Phase-Locked Loop IC mainly includes three blocks which include the following.

Block Diagram
Block Diagram

In the above block diagram, a phase detector generates a DC voltage and this voltage is comparative to the phase dissimilarity among the input signal with frequency ‘fin’ & feedback signal with ‘fout’ frequency. It is a multiplier and generates two frequency-based components on its o/p like the two frequencies sum & difference of two frequencies.

An active LPF is a second component in the above blog diagram that generates a DC voltage on its o/p once the high-frequency component is removed which is present in the phase detector’s output. By using this, the signal can be amplified.

A voltage-controlled oscillator generates a signal with a certain frequency, once no input is provided to it. So, this frequency can be moved to any side by providing a DC voltage to it. Thus, the difference in frequency can be directly proportional to the DC voltage there at the LPF’s output.

The above processes occur until the frequency of the voltage-controlled oscillator is equivalents to the frequency of the i/p signal. So depending on the application, we can utilize either the o/p of active LPS otherwise VCO’s output.

Working of LM565 Phase-Locked Loop IC

In the block diagram of LM565 PLL, both the pins like 2 & 3 where the input analog signal connection can be done however pin2 are used as input whereas pin 3 is connected to GND.

Here, the input signal is given to the phase detector through VCO feedback which evaluates whether both signals are in similar frequency or not. If both the signals are in frequency, then the phase detector provides 0V output & if the frequency is there then this detector provides +Ve o/p voltage.

The phase detector’s o/p voltage is provided to an amplifier for amplifying the voltage signal & this can be given to voltage controlled oscillator. This oscillator produces a waveform where the frequency of this waveform mainly depends on the magnitude of specified input voltage.

When no input is provided to this, then the VCO in free-running mode will generate a signal. The frequency of this signal can be determined through the resistor and capacitor which are connected at pins 8&9.

Once an input signal is provided, then both the input signal frequency & the o/p of VCO can be evaluated. If they are not equal, the phase detector will supply a voltage and that is changed and given to VCO.

So, the signal frequency can be increased or decreased based on the voltage fed to an amplifier. When the modification is done then both the frequencies of the i/p signal & VCO will be equivalent.
In this way, PLL IC functions, the o/p frequency signal of voltage controlled oscillator is always attempts to continue through the i/p signal frequency.

LM565 IC Features & Specifications

The features and specifications of the LM565 Phase Locked Loop mainly include the following.

  • The range of power supply is wide
  • Demodulated o/p is 0.2% linearity
  • Power dissipation Max is1400mW
  • Availability of linear triangle signal through in-phase zero crossings
  • Operating voltage Max is ±12V
  • Temperature ranges from -55ºC to +125ºC
  • TTL & DTL compatible with the input of phase detector & output of square wave
  • Hold in the range can be adjustable from ±1% to above ±60%
  • The range of Operating Voltage ranges from ±5V to ±12V
  • The stability of frequency for the VCO is 200 ppm/°C
  • Range of Storage Temperature from -65°C to +150°C
  • The current power supply is 12.5mA
  • Max operating frequency of VCO is 500 KHz

LM565 Phase Locked Loop IC Circuit

An electronic circuit like a Phase Lock Loop is used to lock the input signal’s phase through the output by maintaining them matched. This can be achieved during a mechanism of closed-loop feedback that evaluates the input signal through the o/p to make the required corrections so that the phase will stay synchronous.

The PLL IC like LM565 is not readily available; however, an alternative well-matched integrated circuit is the NTE989.

LM565 IC Circuit Diagram
LM565 IC Circuit Diagram

The main function of a PLL is to follow an incoming frequency & compare the phase exactly. But, in the above circuit, the feedback loop includes a 16 counter that returns the feedback signal i.e, 16 fold low. Consequently, the phase lock will try to recompense & increase the 16 fold incoming frequency.

Once the inputs signal alters, then the phase detector identifies the transform within frequency & force of the VCO to modify the output. So that the o/p is equivalent to the original i/p frequency, thus removes the fault value from the phase comparator.

The ‘fc’ free-running frequency takes place once the phase-locked loop has no input signal. The frequencies range on which the IC will follow an input signal & remain locked will be the lock frequency. So this series is below or above the voltage-controlled oscillator’s frequency.

In this range, the PLL will follow & lock toward any input frequency. If the range of occurred input signal is out of this lock then the PLL will not track it. When the i/p frequency moves near to the range of the clock, then the phase-locked loop will move into a locked state.

Similarly, when the i/p frequency moves to the frequency of voltage-controlled oscillator then capturing condition will happen. Throughout this time, the PLL IC will be locked & follows any additional changes toward the i/p frequency.

The capture range is nothing but the range of frequency on which a phase-locked loop can capture a signal. Similar to the range of lock, this range will be approximately the free-running frequency. As the PLL captures in a thin band, then it performs like a BPF (band-pass filter).

Input Range Calculation

The maximum revolutions taken by an engine to rotate is approximately 7000 for each minute, & the minimum is 400 revolutions for each minute. The hall sensor for every single revolution of the engine will generate 4 signals

The max frequency is 4 × (7000) / 60 = 500 pulses per second or 466 Hz

The minimum frequency:

4 × (400) / 60 = 26.66 signals for each sec otherwise 26.66 Hz

The free-running frequency like ‘fc’ is the center frequency of the max and min frequencies

Calculation of Ro × Co

Based on the center frequency, the below mentioned formula is used to provide the values for Ro & Co. Since we require the centre frequency “ƒc” to be 266.665

fc = 0.3 / (Ro × Co)

The required fc value is = 266.665

Ro × Co = 0.3/fc => 0.3/ 266.665

Ro × Co => 0.001125

In the above equation, if the ‘C0’ value is set to 1 µF, the ‘Ro’ is 1125.007 Ohms that can be made using a 1KΩ fixed resistor & a 220 Ω preset within series.

Thus, in the above circuit diagram, a TC pin includes a 1µF capacitor & a TR pin includes a 1 kΩ resistor & preset with 220 Ω in series. These will confirm that the phase-locked loop IC can stay a lock in our preferred range of frequency.


The applications of LM565 Phase Locked Loop IC include the following

  • PLL IC is used in communication systems like satellites, radars, FMs, clock generators, FM & FSK demodulation, etc.
  • Synchronization of Data & Tape
  • Modems
  • Coherent Demodulators
  • Decoding of Tone
  • Regeneration of Signal
  • Frequency Division & Multiplication
  • Telemetry Receivers
  • Demodulators of SCA

Thus, this is all about an overview of the LM565 datasheet which includes its definition, pin diagram, specifications, features, working, and circuit working with applications. Generally, LM565 is a PLL IC, used where a phase-locked loop is essential like multiplier/signal frequency divider and FM demodulation. This IC is mainly designed for frequency multiplication, demodulation & frequency division purposes. Here is a question for you, what is the main function of a PLL or Phase Locked Loop?