LSF0108-Q1: Interconversion of 1.8V and 5V CMOS levels,Rpu resistance

Neal Zhu

Part Number: LSF0108-Q1

The conversion between 1.8V and 5V CMOS levels, If the IC output is all push-pull structure, is the resistor Rpu necessary?

8-channel, what do you do with dangling channels?Do not connect?

Thanks!

over 3 years ago

0 Rami Mooti1 over 3 years ago

TI__Mastermind 23393 points

Hey Neal,

The pullup isn't necessary if your application doesn't call for it. The image in the datasheet that you've shared is just showing many different ways to use the LSF0108-Q1 but you aren't limited to the setup shown. The LSF is a passive switch so if the architecture doesn't call for additional pullups outside of the normal pull ups your application would typically have (e.g. I2C).
For the LSF family you can leave unused pins floating:
[FAQ] What should be done with unused I/O pins of the level translator devices?

How many channels do you need? We do have a 4channel and 2 channel AEC-Q100 qualified versions in the in the family.

Thanks,
Rami

0 bkmtech over 3 years ago in reply to Rami Mooti1

Prodigy 230 points

At a more fundamental level, if he has a push pull circuit the pull up is an integral part of the push pull circuit.

Correct me if I am wrong, but you couldn't have a push pull without a push and a pull

0 Emrys Maier over 3 years ago

TI__Guru* 96591 points

As this is shown in the datasheet, with 1.8V being up-translated to 5V, then yes - a pull-up resistor is absolutely necessary in that application. The LSF device cannot up-translate by itself (because it is a passive translator).

Please see this video: https://training.ti.com/translation-lsf-family-0?cu=1134826

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LSF0108-Q1: Interconversion of 1.8V and 5V CMOS levels,Rpu resistance