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LSF0102: Pull up resistor size

Shu-Cheng LIN
Guru 11785 points
Part Number: LSF0102

Hi Sirs,

Sorry to bother you.

We have use LSF0102 on Low pin count serial IRQ signal. (1.8v to 3.3v)

We couldn't got good waveform on A side and B side. 

The end customer have use 8.2K PU resistor that will in parallel to our B side PU resistor.

Our test table as below, did you any idea on here?

A

B

RAC carrier
Pull-high

LPC

220 ohm

1k ohm

8.2k ohm

High 2.4~3.3V
Low 820mV

220 ohm

1.5k ohm

8.2k ohm

High 2.4~3.3V
Low 620mV

150 ohm

1.5k ohm

8.2k ohm

High 2.3~3.3V
Low 440mV

100 ohm

1.5k ohm

8.2k ohm

High 2.4~3.2V
Low 400mV

100 ohm

1.3k ohm

8.2k ohm

High 2.3~3.2V
Low 400mV

100 ohm

820 ohm

8.2k ohm

High 2.5~3.2V
Low 540mV

100 ohm

200 ohm

8.2k ohm

High 3.3V
Low 1.5V

100 ohm

4.7k ohm

8.2k ohm

High 2.2 ~ 3.2V
Low 220mV

1k ohm

4.7k ohm

8.2k ohm

High 2.8 ~ 3.2V
Low 960mV

1.5k ohm

4.7k ohm

8.2k ohm

High 2.8 ~ 3.2V
Low 960mV

4.7k ohm

4.7k ohm

8.2k ohm

High 2.2 ~ 3.2V
Low 2.2V

4.7k ohm

8.2k ohm

8.2k ohm

High 2.1 ~ 3.2V
Low 2.1V

1k ohm

8.2k ohm

8.2k ohm

High 2.6 ~ 3.2V
Low 500mV

1k ohm

6.2k ohm

8.2k ohm

High 2.7 ~ 3.2V
Low 840mV

100 ohm

300 ohm

8.2k ohm

High 3~3.3V
Low 1.2V

100 ohm

390 ohm

8.2k ohm

High 3~3.3V
Low 1V

470 ohm

1k ohm

8.2k ohm

High 3~3.3V
Low 1.2V
  • 0
    TI__Genius 16735 points

    Hi,

    I have assigned this thread to our translation expert to be able to assist you.

    Thanks!

    -Karan

  • 0
    TI__Guru 61970 points

    Hi Shu-Cheng,

    What frequency is this operating at and what are the external cap loading, strength of the driver?

    Line 11 and 12 doesn't make sense to me.

    The LSF is passive translator where the Vol at the output depends on the input Vil and pass FET resistance and current.

    The stronger pullup resistor generates excessive current during the low state which increases the Vol at the output side. However, with weak pullup resistor, the high level may not be reached due to the long RC timing.