74LS00N 74LS02N 74LS04N 74LS08N 74LS10N TTL IC

TRANSISTOR-TRANSISTOR LOGIC INTEGRATED CIRCUIT

74LS family TTL characteristics

Supply: 5V ±0.25V, it must be very smooth, a regulated supply is best*. In addition to the normal supply smoothing, a 0.1µF capacitor should be connected across the supply near the IC to remove the 'spikes' generated as it switches state, one capacitor is needed for every 4 ICs.

* In my experience 74LS ICs usually work successfully with a 4.5V battery supply in simple and undemanding low frequency circuits but I certainly don't recommend this for any circuit with a serious purpose as it's outside the rated voltage range.

Inputs 'float' high to logic 1 if unconnected, but do not rely on this in a permanent (soldered) circuit because the inputs may pick up electrical noise. 1mA must be drawn out to hold inputs at logic 0. In a permanent circuit it is wise to connect any unused inputs to +Vs to ensure good immunity to noise.

Outputs can sink up to 16mA (enough to light an LED), but they can source only about 2mA. To switch larger currents you can connect a transistor.

Fan-out: one output can drive up to 10 74LS inputs, but many more 74HCT inputs.

Gate propagation time: about 10ns for a signal to travel through a gate.

Frequency: up to about 35MHz (under the right conditions).