74HC logic gates: 74HC00, 74HC02, 74HC04, 74HC08, 74HC14, 74HC32 and 74HC86 pinouts and limits

The two digits after 74HC name the function, and they are the same at every maker: 00 is a quad 2-input NAND, 02 a quad NOR, 04 a hex inverter, 08 a quad AND, 14 a hex Schmitt inverter, 32 a quad OR, 86 a quad XOR. TI prints an SN prefix and a package letter after the number: SN74HC00N is the plastic DIP, SN74HC00D the SOIC. Nexperia drops the prefix (74HC00D, 74HC00PW) and no longer lists a DIP for any of these parts.

A T after HC (74HCT00) marks the TTL-input version. It has the same pins, but it runs only from 4.5 to 5.5 V and takes any input above 2.0 V as high. 74LS and plain 7400 parts belong to the older bipolar families; this page covers HC and HCT only.

On ratings the two makers agree line for line: 7 V absolute maximum on the supply, 2 to 6 V recommended, ±25 mA from any one output and ±50 mA through the VCC or ground pin for the whole chip. They part on temperature. TI's commercial SN74HC parts are rated −40 to 85 °C, except the SN74HC08, which TI now rates to 125 °C; every Nexperia 74HC part here is rated to 125 °C.

The 50 mA pin limit matters more than the 25 mA one. Four outputs each lighting an LED at 15 mA are inside the per-output figure and over the pin figure. Keep the total under 50 mA, and for guaranteed logic levels keep each output near the 4 mA the tables are written for.

A plain HC input sees anything below 1.35 V as low and anything above 3.15 V as high when VCC is 4.5 V. Both makers give the same pair, and both scale with the supply: at 6 V the limits are 1.8 V and 4.2 V. In between the state is undefined, and an input parked there makes the chip draw extra current. That is why an unused input must go to VCC or ground, never left open.

The output side is symmetrical. At 4.5 V and 4 mA an output stays above 3.98 V when high and below 0.26 V when low, on both makers' sheets. Propagation delay at 4.5 V into 50 pF is 17 to 25 ns maximum at 25 °C, depending on the gate and the maker; the 74HC14 is the slowest at 25 ns on both sheets. Nexperia's current 74HC00 sheet gives no 25 °C maximum at all, only 23 ns over −40 to 85 °C, so design to that.

A plain HC input also wants a fast edge. TI sets a 500 ns maximum rise or fall time at 4.5 V, and Nexperia 139 ns per volt; a slow RC edge or a sensor output sits in the undefined band too long, and the output can switch more than once on the way through. Use a 74HC14 for those signals.

Four NAND gates. Gate 1 takes pins 1 and 2 and drives pin 3; gate 2 takes 4 and 5 and drives 6. On the other side the order turns round: output 3Y on pin 8 with inputs on 9 and 10, output 4Y on 11 with inputs on 12 and 13. The output is low only when both inputs are high.

Because NAND can make any other gate, the 74HC00 is the usual spare-parts chip: tie both inputs of a gate together for an inverter, or cross-couple two gates for a set-reset latch with active-low inputs.

The 74HC02 has its own pin arrangement. Pin 1 is the output 1Y, with its inputs on pins 2 and 3; gate 2 drives pin 4 from pins 5 and 6. On the right side, gate 3 takes pins 8 and 9 and drives 10, and gate 4 takes 11 and 12 and drives 13. TI and Nexperia draw it the same way. The output is high only when both inputs are low.

So a 74HC02 never drops into a 74HC00, 08, 32 or 86 socket, and the reverse is no better. Fitted in the wrong place, its outputs fight whatever drives those input pins.

Six inverters, each input on an odd pin and its output on the next: 1 to 2, 3 to 4, 5 to 6 down the left side, then 9 to 8, 11 to 10, 13 to 12 on the right. Delay at 4.5 V is 19 ns maximum on TI's sheet and 17 ns on Nexperia's. Its inputs have the plain 1.35 V and 3.15 V limits, so feed it clean, fast edges.

Same pins as the 74HC00, and the output is high only when both inputs are high. On TI's sheet it is a little slower than the 74HC00: 20 ns maximum at 4.5 V against 18 ns. Nexperia gives 18 ns for both. TI rates its SN74HC08 from −55 to 125 °C, wider than the other SN74HC parts here.

The 74HC14 has the 74HC04 pinout, but each input has two thresholds instead of one. A rising input switches the output low when it passes VT+, and a falling input switches it back high only when it drops below VT−. The gap between them, the hysteresis, is what lets the chip take a slow ramp or a noisy signal and give a clean edge.

Both makers describe the same behavior with different numbers. At 4.5 V TI gives VT+ from 1.55 V to 3.13 V (typical 2.5 V) and VT− from 0.9 V to 2.45 V (typical 1.6 V). Nexperia gives VT+ from 1.7 V to 3.15 V (typical 2.38 V) and VT− from 0.9 V to 2 V (typical 1.4 V). Hysteresis is at least 0.4 V on both sheets; TI allows up to 2.1 V, Nexperia up to 1.4 V. Neither sheet has a 5 V row: the nearest are 4.5 V and 6 V.

To design to both, a signal must fall below 0.9 V to be read as low and rise above 3.15 V to be read as high, and noise on it must stay under 0.4 V peak to peak. TI states the first two rules in its input section, using VT− minimum and VT+ maximum, and the noise rule from the minimum hysteresis.

TI lists no input rise-time limit for the 74HC14 and Nexperia calls the rise and fall times unlimited. A slow input still costs supply current while it passes through the thresholds; Nexperia plots that extra current against VCC.

Same pins as the 74HC00. The output is high when either input is high, or both. Delay is 20 ns maximum at 4.5 V on TI's sheet and 18 ns on Nexperia's.

Same pins as the 74HC00. The output is high when the inputs differ, which makes the 74HC86 the chip for a controllable inverter (tie one input high and the gate inverts, tie it low and the signal passes), a parity check or an edge detector. It is the slowest quad here on Nexperia's sheet, 24 ns maximum at 4.5 V against 18 ns for the 74HC02, 08 and 32; TI gives 20 ns.

• Glue logic on a 2 to 6 V board: gating a clock, combining enable signals, inverting a reset line.
• Cleaning up a slow or noisy edge with a 74HC14: an RC-debounced push button, a phototransistor, a long cable.
• A cheap oscillator or clock from one 74HC14 gate, a resistor and a capacitor, worked through below.
• Buffering a weak signal into several loads: one HC output drives many HC inputs, which draw at most 1 µA each.

They are a poor choice for driving relays, motors or more than a few milliamps of LED current, and a 3.3 V output cannot be trusted to drive a 74HC input on 5 V (see further down). The logic families lesson compares HC with the other CMOS and TTL families.

One gate of a 74HC14 with a resistor from its output back to its input and a capacitor from the input to ground. Three AA cells give 4.5 V, the supply both datasheets specify the thresholds at, so the numbers below come straight from the tables.

For a set frequency, put a trimmer in series with a smaller fixed resistor and tune it on the bench. The RC time constant lesson derives the charging curve behind steps 2 and 3.

A 3.3 V microcontroller wired to a 74HC gate on 5 V is a common trap. At 4.5 V a plain HC input needs at least 3.15 V to count as high, which leaves 0.15 V of margin for a perfect 3.3 V output. Neither maker prints a 5 V row; between the 4.5 V and 6 V limits (3.15 V and 4.2 V) the requirement at 5 V works out to about 3.5 V, above the 3.3 V level.

The fix is one of three: power the 74HC gate from 3.3 V too (it is specified from 2 V), use the 74HCT version of the same chip, whose 2.0 V threshold leaves 1.3 V of margin, or use a level shifter. Our 3.3 V to 5 V level shifter guide compares the options. Going the other way, a 5 V HC output into a 3.3 V input needs a divider or a shifter, never a direct wire.

• Fit 100 nF from pin 14 to pin 7, right at the chip, as TI's power section asks. Fast HC edges need it even at low clock rates.
• Tie every unused input to VCC or ground. An open CMOS input floats into the undefined band, and the gate can oscillate or draw current. Unused outputs can stay open.
• Check the part number before you fit a 74HC02. It is the only chip here whose pin 1 is an output.
• For an input from a switch, a sensor or a long wire, use a 74HC14, not a 74HC04 or a 74HC00 gate wired as an inverter.
• An LED straight off an output is fine at a few milliamps with a series resistor. For 15 mA or more per LED, or several at once, add a transistor so the chip stays under its 50 mA pin limit.

The IC power and decoupling and pull-up and pull-down lessons cover the first two points in detail.

Within a part number, TI and Nexperia parts swap freely. Across part numbers the only safe swap is a 74HC14 for a 74HC04; the HCT parts swap for HC on a 5 V board.

1. Power the chip from 5 V with every input tied to ground and measure the supply current. It should be a few microamps; TI allows 20 µA at 6 V up to 85 °C. Milliamps means an input is floating or the part is damaged.
2. Walk each gate through its truth table with two wires to VCC or ground and a meter on the output: near 5 V for a 1, near 0 V for a 0.
3. For a 74HC14, feed one input from a potentiometer across the supply and turn it slowly up, then down. The output should flip low somewhere near 2.5 V going up and back high near 1.6 V coming down (TI's typical figures at 4.5 V; a given chip may sit anywhere inside the limits), and never chatter in between.
4. Build the oscillator above on one gate and check the output on a scope: a square wave near 1.22 kHz on 4.5 V. Anything from about 481 Hz to 2.81 kHz is still inside the datasheet limits.

The oscilloscope measurements lesson covers reading the frequency and duty cycle off the screen.

Keep a 74HC00 and a 74HC14 in the drawer: between them they cover most glue logic and every slow or noisy input. Check the 74HC02 pinout every time you use one, power HC gates from the same rail as whatever drives them, and buy the HCT version when a 3.3 V part has to drive a 5 V gate. Use the 74HC14 oscillator for clocks and tones where the exact frequency does not matter or can be trimmed, and a crystal or a timer IC where it does.

The DIP versions of all seven are stocked by most Indian component sellers, often as TI SN74HC parts and sometimes with no maker named. Nexperia parts come in SO14 only, so buy those for a PCB. Check the full number on the body, because a 74HC14 listing may turn out to be a 74HCT14 or an LS part. Our guide to buying electronic components in India compares ten online sellers and covers how to spot fakes.