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

over 6 years ago

0 Karan Kotadia over 6 years ago

TI__Genius 16735 points

Hi,

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

Thanks!

-Karan

0 ShreyasRao over 6 years ago

TI__Guru 63250 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.

Logic

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LSF0102: Pull up resistor size