Dual JK flip-flop with set and reset — the field-replaceable workhorse
The Texas Instruments CD74HCT109M is a dual positive-edge-triggered JK flip-flop in a 16-SOIC package, with independent set (preset) and reset inputs per element and complementary outputs. Clock frequency hits 54 MHz, with a propagation delay of 40 ns at 4.5V into a 50 pF load. Quiescent supply current is a lean 4 µA, and each output can source or sink 4 mA — enough to drive standard CMOS logic inputs or a single low-current LED indicator on a panel. The operating temperature range is -55°C to 125°C.
What the ratings mean for the BOM
Output drive is 4 mA per pin. Input capacitance is 10 pF per the datasheet — factor that into your clock-line loading if you are daisy-chaining multiple flip-flops on a single clock trace. At 54 MHz, a few extra pF of trace + input capacitance can start to round the clock edges.
Temperature grade and deployment environment
Rated for -55°C to 125°C ambient operation, this part belongs in equipment that sees thermal cycling from cold-soak to under-hood heat: avionics LRUs, missile guidance electronics, satellite telemetry boards, downhole drilling instrumentation, and outdoor base-station RF control logic. The 16-SOIC package is surface-mount, so it can be conformal-coated for humidity and vibration resistance. No lab bench needed to swap it — a standard soldering iron and a steady hand are enough for field replacement, though a hot-air station makes desoldering cleaner.