LSF0108: LSF0108

Shlomi Yehezkia

Mastermind 6150 points

Part Number: LSF0108

Hi Team,

Please review the attached design, I want to transfer IO signal from 3.3V to 1.8V but the buffer not work.

My connection is ok?

Thanks,

Shlomi

LSF0108.docx

over 7 years ago

0 Emrys Maier over 7 years ago

TI__Guru* 97066 points

Hello Shlomi,

The LSF0108's bias circuit is connected incorrectly. I would recommend watching these two videos that explain the operation in detail:

Understanding the Bias Circuit for the LSF Family

Using the Enable Pin with the LSF Family

Your circuit:

Note that the green circled area is where the primary mistake is.

Additionally, I don't see any pull-up resistors on pins 11-16 -- are these all unidirectional signals?

You might also want to check out this video:

Up Translation with the LSF Family

0 Shlomi Yehezkia over 7 years ago in reply to Emrys Maier

Mastermind 6150 points

Hi,

I need translator (8 Channel) with Ability to control the EN pin.

"Additionally, I don't see any pull-up resistors on pins 11-16 -- are these all unidirectional signals?" - Yes

Thanks,

Shlomi

0 Emrys Maier over 7 years ago in reply to Shlomi Yehezkia

TI__Guru* 97066 points

You can control the enable pin of the LSF device, please watch the video entitled "Using the Enable Pin with the LSF Family" that I linked above.

0 Shlomi Yehezkia over 7 years ago in reply to Emrys Maier

Mastermind 6150 points

Hi,

I connected the En pin to R677 following TI request and still got 2.4V in the output.

My regulator is to 1.8V as below, why the LSF connection damaged my regulator?

Thanks,

Shlomi

LSF0108 sch.docx

0 Emrys Maier over 7 years ago in reply to Shlomi Yehezkia

TI__Guru* 97066 points

Hi Shlomi,

Is your regulator driving anything else in the system? The current from the LSF (coming out of pin 2) will need to sink somewhere -- typically this goes into the feedback circuit or other devices downstream on the same rail. If those are not available, then the regulator could have problems maintaining regulation due to the current going _into_ the output -- most regulators don't work in that condition. To ensure the regulator will work, you can add a resistor to the output, adding a path to ground for the current.

You can see how this current flows in the video:

Understanding the Bias Circuit for the LSF Family

Logic

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LSF0108: LSF0108