Dual decade ripple counter for frequency division and event counting
Each of the two independent counters divides by ten, triggered on the negative edge of the clock input. The asynchronous reset forces all outputs low immediately, independent of the clock state, which is useful for power-on initialization or fault recovery in timing chains. Rated for a maximum count rate of 27 MHz, the part handles frequency division up to the low-MHz range — suitable for dividing a 27 MHz reference clock down to 2.7 MHz, 270 kHz, and so on. The supply range of 4.5 V to 5.5 V aligns with standard 5 V TTL/CMOS rails, and the operating temperature range of -55°C to 125°C qualifies it for military, avionics, and downhole instrumentation where the board sees extreme thermal cycling. The 74HCT series provides LSTTL-compatible input thresholds with CMOS output swing, so it can directly drive standard 74HCT or 74LS loads without level translation.
The 27 MHz count rate is the maximum clock frequency at which the counter reliably increments. In a frequency divider chain, this sets the upper bound on the input clock. The asynchronous reset (active-high) clears all four bits of each counter without waiting for a clock edge, which guarantees a known state at power-up or after a reset pulse — no dead cycles. Because the counter is ripple-through, the propagation delay from clock to the most significant bit is the sum of the delays through each stage. For timing closure, budget the worst-case propagation delay from the datasheet when cascading counters or sampling the output synchronously.
As an active, widely-used 74HCT logic part, the CD74HCT390M96 is stocked by multiple independent distributors. The part is sourced to order through our supply chain, with no minimum order quantity restrictions typical of broker channels.