What this PLL brings to the board
The Texas Instruments CD74HCT4046AE is a Phase-Locked Loop (PLL) with an integrated VCO, built on the 74HCT logic family with CMOS-compatible inputs and outputs. It operates from a 4.5 V to 5.5 V supply, making it a direct fit for 5 V TTL/CMOS systems. The single-circuit device provides a 1:4 input-to-output ratio and supports a maximum frequency of 38 MHz. Packaged in a 16-pin PDIP (0.300" wide, 7.62 mm pitch) for through-hole mounting, it is suited for frequency synthesis, clock recovery, and motor-speed control in industrial, telecom, and instrumentation applications where a wide temperature range is required.
The 38 MHz maximum frequency sets the upper bound for the VCO and phase-detector operation. In a typical frequency-multiplier loop, the input reference must stay well below this limit to leave margin for the VCO's capture range and lock time. For designs clocking a microcontroller or FPGA from a lower-frequency crystal, this part can multiply a 1–10 MHz reference up to the 38 MHz ceiling without external dividers. If your target output exceeds 38 MHz, you need a faster PLL — this one will not lock.
Military temperature grade: deployment envelope
The 74HCT family maintains CMOS noise margins across this range, but the VCO centre frequency and phase-detector gain will shift with temperature — budget for a wider lock range in the loop filter design. At 125°C junction, leakage currents increase; the loop filter capacitor should use X7R or C0G dielectric to avoid capacitance derating.
For dual-sourcing flexibility, the CD74HCT7046AE is a pin-compatible variant — same 38 MHz max, same temperature range — but with a 1:2 input-to-output ratio and a different phase-detector architecture, so verify loop stability before substituting.