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.
38 MHz ceiling and what it means for the loop
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
Rated for -55°C to 125°C operating temperature, the CD74HCT4046AE qualifies for avionics, satellite, downhole drilling, and military ground-vehicle electronics. 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.
Lifecycle and sourcing reality
Texas Instruments lists the CD74HCT4046AE as Active and ROHS3 compliant. There is no announced end-of-life or last-time-buy window, so the part can be specified into new production without near-term obsolescence risk. 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.