CD74HC4046AE datasheet by Texas Instruments

CD74HC4046AE Frequently Asked Questions (FAQs)

• What is the recommended power-up sequence for the CD74HC4046AE?
  The recommended power-up sequence is to apply VCC before applying any input signals. This ensures that the internal bias circuitry is established before the PLL is enabled.
• How do I choose the correct values for the loop filter components (R1, R2, C1, C2)?
  The loop filter component values depend on the desired PLL bandwidth, phase margin, and lock time. TI provides a PLL calculator tool to help with component selection. Additionally, the datasheet provides a general guideline for component selection.
• What is the maximum input frequency that the CD74HC4046AE can handle?
  The maximum input frequency is typically limited by the internal oscillator frequency, which is around 1 MHz. However, the PLL can track input frequencies up to 10 MHz with proper loop filter design and component selection.
• How do I ensure that the PLL locks to the correct frequency?
  To ensure the PLL locks to the correct frequency, ensure that the input signal is within the PLL's capture range, and the loop filter is properly designed. Additionally, the datasheet recommends using a pull-up resistor on the PD (phase detector) output to improve lock detection.
• What is the purpose of the PD (phase detector) output, and how do I use it?
  The PD output indicates the phase difference between the input signal and the VCO (voltage-controlled oscillator) output. It can be used to monitor the PLL's lock status or to implement a lock detect function.