LSF0108: shift high level issue

Tommy Tzeng

Part Number: LSF0108

Tool/software:

Hi Team,

may we know what is the cause? why does a low level happen on the B side when a high level of 3.3v happen on B side? thanks for your support and learn from you.

waveform and schematic as below:

PORTPROMPT_LSF0108.pdf

6 months ago

+1 Clemens Ladisch 6 months ago

Guru 317450 points

In the schematic, these pins are not connected to anything. But I guess that the secret device that you have not shown does not have enough drive strength to sink the current through both pull-up resistors (1.2 V / 100 Ω + 3.3 V / 499 Ω = 18.6 mA).

+1 Jack Guan 6 months ago

TI__Mastermind 41266 points

Hi Tommy,

Similarly to Clemens' response, please consult with the driver datasheet if this leakage current is acceptable. The pullup resistors at A/B side should be chosen based on desired speed/ power tradeoffs, see below formula for estimation:

Regards,

Jack

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LSF0108: shift high level issue