Omit the 74LV1T125 on a diy board; & 74LV1T125 vs transistor

[mikemontauk]

Output 17 (PTB1, MKL26Z64VFT4 pin 28) on a DIY Teensy LC will operate normally as a digital, analog, i2c, pwm, or touch pin if I do not include the 74LV1T125 circuit correct?

Follow-up: Regarding 74LV1T125 it appears to me that 74LV1T125 is typically used in "Up translation" 3.3 V to 5.0 V at VCC = 5.0 V, what is the benefit of the 74LV1T125 over a transistor or mosfet? Is it the plurality of output states? e.g. people feed the 74LV1T125 different voltages via analogueWrite to change the 17(VIN) output voltage from 1.8V to 5V in real time?

 

[PaulStoffregen]

what is the benefit of the 74LV1T125 over a transistor or mosfet?

The 74LV1T125 on Teensy LC is mainly meant to send a 5V signal to WS2812 addressable LEDs. A buffer chip gives similarly fast rise and fall times, which preserves the pulse width.

With a single N-channel or NPN transistor, you tend to get fast fall time but much slower rise time, and the rise time slowness can vary quite a lot depending on the type of wire or other load connected. Different speed on rise vs fall effectively changes the pulse width.

 

[LenSamuelson]

Correct, the LC processor can use the pin according to the processor's settings. It is a 3.3V pin, and as seen in the schematic could be used as an I/O pin without difficulty. The LC uses a 74LV1T125 to provide a 5V tolerant output signal, most useful for driving addressable LED strings.

The 74LVT125 has a three-state "push-pull" output stage. When it's enabled it will drive its output to "high" or "low" quickly. Disabled puts it in a high impedance state.

A transistor or FET level translator would be quick to pull its output "low" but its "high" output state is really a high impedance state. So the output would "drift high" rather than being driven.

I have not seen a 74LV1T125 used for driving more than "high", "low" or high impedance.

 

[mikemontauk]

Thank you, Paul. I'm going to look into the comparative rise times of the two device classes as a future learning objective.

 

[mikemontauk]

Thank you, LenSamuelson. I'm going to omit the 74LV1T125.

When you said, "A transistor or FET level translator would be quick to pull its output "low" but its "high" output state is really a high impedance state. So the output would "drift high" rather than being driven," it was a bit over my head. I'm going to continue reading on those topics and try to understand them further.