LSF0108: for UART SPI I2S?

Wipop Panyatipsakul

Part Number: LSF0108
Other Parts Discussed in Thread: TXU0204, TXU0304, TXB0108

Hi all,

I've already designed the board using LS0108 for UART, SPI, I2S. The method is to translate the voltage between 1V8 <-> 3V3.

According to this [question about LSF0204] which I just asked, It seems that I just misunderstand the mechanism of LSF family voltage translator.

Is it necessary to modify this circuit using pullup R or any modifying can be applied?

over 1 year ago

+1 Clemens Ladisch over 1 year ago

Guru 303830 points

In general, all LSF outputs require pull-up resistors. (Without them, you will not get any output voltage higher than VrefA.) See section 5.2 of the Voltage-Level Translation With the LSF Family Application Report.

All your signals are unidirectional. Using unidirectional translators like the TXU0204/TXU0304 would be simpler and more robust.

0 Jack Guan over 1 year ago

TI__Mastermind 32776 points

Hey Wipop,

I stand alongside with Clemens' take on this one. The LSF family devices won't buffer or redrive your input signals since it is only an internal FET that connects the output directly to input. Using unidirectional/ direction controlled translators will allow for better signal integrity and require less design requirements.

Here is a good place to start: Voltage Translation Application Quick Reference

Regards,

Jack

0 Wipop Panyatipsakul over 1 year ago

Prodigy 60 points

Hi, thanks for your supports, I'll use these info. to improve the next board design.

Can these 2 ways be applied?

- Temporary add 1K R pullup array onto the board at the B side of LSF.

- Use TXS0108 TXB0108

+1 Clemens Ladisch over 1 year ago in reply to Wipop Panyatipsakul

Guru 303830 points

Pull-ups at the B side will work. But I do not know if 1 kΩ is to small or too high (this depends on the desired speed and on the capacitance of your board; you probably have to check with an oscilloscope).

The TXS and TXB are not P2P-compatible with the LSF. Both might work, but have restrictions on what loads they can drive (see their datasheets).

0 Wipop Panyatipsakul over 1 year ago in reply to Clemens Ladisch

Prodigy 60 points

OK, Thanks for your support.

Clemens Ladisch said:
The TXS and TXB are not P2P-compatible with the LSF.

Yes, its not P2P. It may be used for the next design.

0 Clemens Ladisch over 1 year ago in reply to Wipop Panyatipsakul

Guru 303830 points

For unidirectional signals, prefer the TXU translators.

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LSF0108: for UART SPI I2S?