74244 is a non-inverting octal buffer. Its output can be disabled in groups of four if they are not being used.
Lines #: 8
Groups #: 2
Output type: CMOS push-pull
ESD protection: Yes
Propagation delay @ 5V: 11ns
- Min: 4.5V
- Max: 5.5V
Vih @ 5V
- Typical: 1.6V
- Minimum: 2.0V Io Max.: 35mA
An unique feature about 74HCT245 that is not present in other similar buffers is that, the 8 lines can be split into two buses with up to 4 lines in each bus. The groups are:
- Group1: 1A0, 1A1, 1A2, 1A3
- Group2: 1A0, 2A1, 2A2, 2A3
Each of the groups can be separately tristate-ed using respective output enable lines. Thats right, each of these groups have their own output enable lines unlike other similar octal buffer ICs.
74HCT245 can output a maximum current of 35mA. This can be used to drive heavier loads that microcontroller i/o pins cannot drive directly.
3.3V -> 5V Level shifter
Typical Vih for 74HCT244 is 2V which is way below 3.3V. 74HCT244 can be used as 3.3V -> 5V level shifter. 74HCT244 is better than 74HC244 in 3.3V to 5V level shifting because 74HCT series is compatible with TTL logic rather than CMOS logic.
5V -> 3.3V level shifter
Maximum input voltage for 74HCT245 cannot be greater than Vcc according to the specification.
But it can be tricked into accepting voltages greater than Vcc. 74HCT245 has ESD protection diodes on input pins. These diodes come into play when input voltage is greater than Vcc. These clamping diodes can take maximum current of 20mA. This means that a current limiting resister can be used to keep the current below 20mA at 5V. Current limiting resistor of 500ohms would work.
The problem with this trick is, it increases the propagation delay. It is fairly useful for low speed circuits. The lower the resistor the better.
For high speed circuits, use 74ACT244, 74ACT245, 74HCT244, 74HCT245.