LANSDALE Semiconductor, Inc.

ML12202

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Page 7 of 11

Issue A

For FC = HIGH:

fr lags fp in phase OR fp>fr in frequency

When the phase of fr lags that of fp or the frequency of fp is greater than fr, the

φP output will remain in a HIGH state while the

φR output will pulse from LOW to HIGH. The output pulse will reach a minimum 50% duty cycle under a 180° out of phase

condition.The signal on

φR indicates to the VCO to decrease in frequency to bring the loop into lock.

fr leads fp in phase OR fp<fr in frequency

When the phase of fr leads that of fp or the frequency of fp is less than fr, the

φR output will remain in a LOW state while the φP

output pulses from HIGH to LOW. The output pulse will reach a minimum 50% duty cycle under a 180° out of phase condi-

tion.The signal on

φP indicates to the VCO to increase in frequency to bring the loop to lock.

fr = fp in phase and frequency

When the phase and frequency of fr and fp are equal, the output

φP will remain in a HIGH state and φR will remain in a LOW

state except for voltage spikes when signals are in phase. This situation indicates that the loop is in lock and the phase compara-

tor will maintain the loop in its locked state.

When FC = LOW, the operation of the phase comparator is reversed from the above explanation.

For FC = LOW:

fr lags fp in phase OR fp>fr in frequency

When the phase of fr lags that of fp or the frequency of fp is greater than fr, the

φR output will remain in a LOW state while the

φP output will pulse from HIGH to LOW. The output pulse will reach a minimum 50% duty cycle under a 180° out of phase con-

dition.The signal on

φP indicates to the VCO to increase in frequency to bring the loop into lock.

fr leads fp in phase OR fp<fr in frequency

When the phase of fr leads that of fp or the frequency of fp is less than fr, the

φP output will remain in a HIGH state while the

φR output pulses from LOW to HIGH. The output pulse will reach a minimum 50% duty cycle under a 180° out of phase condi-

tion. The signal on

φR indicates to the VCO to decrease in frequency to bring the loop to lock.

fr = fp in phase and frequency

When the phase and frequency of fr and fp are equal, the output

φP will remain in a HIGH state and φR will remain in a LOW

state except for voltage spikes when signals are in phase. This situation indicates that the loop is in lock and the phase compara-

tor will maintain the loop in its locked state.

The FC pin controls not only the phase characteristics, but also controls the fOUT test pin. The FC pin permits the user to moni-

tor either of the phase comparator input signals, fr or fp, at the fOUT output providing a test mode where the programming of the

dividers and the output of the counters can be checked. When FC is HIGH, fOUT = fr, the programmable reference divider out-

put. When FC is LOW, fOUT = fp, the programmable divider output.

Hence,

If VCO characteristics are like (1), FC should be set HIGH or OPEN.

fOUT = fr

If VCO characteristics are like (2), FC should be set LOW.

fOUT = fp