# HC vs LVC for 3.3V Logic

I am designing a circuit in which Vdd=3.3V. I have checked datasheets of hex inverters 74HC04 and 74LVC04 and both of these can work good at 3.3V logic circuits. If I have to select one of them then which one is recommended?

• since you did not specify any operational parameters, then either one is good. Feb 16 '19 at 1:11
• it will be used as signal buffers, so noise rejection as well as output current would be important parameters Feb 16 '19 at 1:15
• Check the propagation delay specs for the two chips. If your signal rate is above 1 MHz, this will probably be the biggest difference between them for you. Feb 16 '19 at 1:20
• My signal switching frequency is less than 25kHz. Feb 16 '19 at 1:22
• examine the shoot-thru charge. 10nH inductances and 10mA currents that rise in 100 picoseconds --- cause 1 volt ground upsets, and ghastly emi... V = L* dI/dT Feb 16 '19 at 2:36

74LVCxx is designed to work at 3.3 volts, with a working range of 1.8 to 3.6 volts. 74HCxx can work at 3.3 volts, with a range of 2 to 5.5 volts, and is considered as being "5 volt logic". The 74HCxx series is limited to ~20MHZ but has strong output drivers with a +/- 25 mA limit. We used them to drive bi-color LED's on the high-side. With proper decoupling capacitors and light loads ground bounce is minimal.

The HCT series was designed to be compatible with older 74LSxx logic which without pull-up resistor could not source a voltage over Vcc - 1.2 volts. A logic 'high' for the 74LSxx series was ~ 3.75 volts. HCT and ACT could work with that, but not 74HC or 74AC. A 4.7K or 10K pull-up resistor allowed for 'mixed' 5 volt logic families with various loading and drive capabilities.

The 74LVCxx series is 10 times faster. Rise and fall times are a couple of nanoseconds. Ground bounce can be significant if data outputs have most any capacitive loading. A more elaborate decoupling scheme is needed. Termination resistors may be needed.

I would avoid the speed Demon 74LVCxx in favor of the much more tame 74HCxx / 74HCTxx series, but the 74HCTxx is not meant to work with 3.3volt logic. The exception would be clocking rates above 20MHZ up to 200MHZ, but then the board layout is much more complex as well.

• Would the HCT series perhaps be more suitable for this task, since it's explicitly designed to work with lower input voltages than HC? Or is that only really relevant when using it as a level shifter? Feb 16 '19 at 20:50
• @Hearth The HCT series was designed to be compatible with older 74LSxx logic which without pull-up resistor could not source a voltage over Vcc - 1.2 volts. A logic 'high' for the 74LSxx series was ~ 3.75 volts. HCT and ACT could work with that, but not 74HC or 74AC.
– user105652
Feb 16 '19 at 20:55
• The LVC logics were 5V input tolerant. The LVC1G's added 5V operation and slowed the clock edges down. Mar 5 '20 at 3:51