LSF0204D: Level conversion problem

Shinya Kume

Prodigy 10 points

Part Number: LSF0204D
Other Parts Discussed in Thread: TXU0304

Hello,

I am posting this because the Auto-direction voltage translators (LSF0204D) are not working properly.

Control the IC with 1.8V.

Inputs and outputs four signals from the CPU for SPI communication.

Convert the CPU signal (3.3V) and IC signal (1.8V) using LSF0204D.

Three signals (SDO/SCK/CS) from the CPU can be converted from 3.3V to 1.8V.

The signal (SDI) from the IC cannot be converted from 1.8V to 3.3V.

Please let me know if I am using it incorrectly.

Best regards,

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 317000 points

Section 10.2.1.2.1 of the datasheet says that "pull-up resistors are required to pull the Bn outputs to Vpu".

The LSF is a passive switch. The TXU0304 would be more robust in this application.

0 Shinya Kume over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Thank you for your reply.
I will implement a pull-up resistor and verify it.
I have also purchased TXU0304, so I will verify it when I get it.

0 Jack Guan over 1 year ago in reply to Shinya Kume

TI__Mastermind 40726 points

Hi Shinya,

Thanks for providing the clear waveform results. Please let us know if any updates regarding testing with pullups or any further questions regarding the TXU0304.

Regards,

Jack

0 Shinya Kume over 1 year ago in reply to Jack Guan

Prodigy 10 points

Hello,

I report the results of the test with SDI pulled up.
As a result, 3.3V is always output and the signal cannot be seen.

Upload the circuit and waveforms.

TXU0304 has not arrived yet.

I'll test it when I get it.

Best regards,

Shinya

0 Clemens Ladisch over 1 year ago in reply to Shinya Kume

Guru 317000 points

220 Ω is probably too strong (the device driving the SDI line must be able to sink all the current). Try values somewhere between 1 kΩ and 10 kΩ, depending on the required speed.

0 Shinya Kume over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Hello Clemens,

Thank you for your reply.

I tested by changing the pull-up resistor value.
When it is 10kΩ, it will not be 0V but 0.7V.
Is it possible to set this to 0V?

Will it be 0V when using TXU0304?
I plan to get TXU0304 on February 15th.

0 Jack Guan over 1 year ago in reply to Shinya Kume

TI__Mastermind 40726 points

Hey Shinya,

I am assuming there isn't an offset to the signal on the input waveforms.

The high VOL that you are seeing is directly related to the high VIL (as shown in the "before conversion" waveforms) that is being inputted into the device. Are you able to configure the drive strength of your driver to be stronger/ try an alt. driver to see if a lower VOL can be achieved? You may see Factors Affecting VOL for TXS and LSF Auto-bidirectional Translation Devices explaining the direct dependency the VIL has on the VOL of the LSF.

The VOL will be closer to 0V if TXU was to be used since it has buffering architecture driving the outputs high/low, though the below requirements would need to be met for the device to see an input logic low:

Regards,

Jack

0 Shinya Kume over 1 year ago in reply to Jack Guan

Prodigy 10 points

Hello Jack,

Thank you for your quick reply.

I understand that the problem may be due to the low driving ability of the current driver.

Since there is no substitute, I will test it with TXU.

Please let me confirm about TXU.
Example) In the case of 1.8V → 3.3V, is there a problem with the input waveform below?

Your comment:

→ Does this mean that a 0V signal needs to be raised to 0.5V?

Best Regards,

Shinya

0 Clemens Ladisch over 1 year ago in reply to Shinya Kume

Guru 317000 points

With a 1.65 V (≈ 1.8 V − 10 %) supply, the TXU requires that low-level input signals go below 0.35 V, and that high-level input signals go above 1.13 V.

The input waveform shown above is fine; it certainly goes below and above the input thresholds.

0 Shinya Kume over 1 year ago in reply to Clemens Ladisch

Prodigy 10 points

Hello, Clemens

Thank you for your reply.

OK,

The TXU will arrive tomorrow so I will test it.

I'll report back on the results.

Thank you,

Shinya

0 Jack Guan over 1 year ago in reply to Shinya Kume

TI__Mastermind 40726 points

Hey Shinya,

Should any issues arise with the TXU0304, please start a new thread as this current one will be closed since solution has been proposed.

Regards,

Jack

0 Shinya Kume over 1 year ago in reply to Jack Guan

Prodigy 10 points

Hello,

I used TXU0304 and it worked fine.
Thank you for your support.

Best Regards,

Shinya

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LSF0204D: Level conversion problem