ISO1541: I2C Falling Time Fail

Jim CHEN

Expert 4795 points

Part Number: ISO1541

Dear Team,

My customer is using ISO1541 on their board design.

But the falling time of I2C cannot meet the spec.

Do you have any suggestion or idea to solve this problem?

Thank you.

	VDD
Measured Result	5.06V

CLK

Frequency

TLow

THigh

Specification

<400KHz

>1.3us

>0.6us

20~300ns

20*(VDD/5.5V)~300ns

18.4~300ns

Measured Result

244.9KHz

1.631us

2.259us

181ns

13.54ns

DATA

	Tsu:dat	Thd:dat	Tsu:sta	Thd:sta	Tsu:sto	Undershoot
Specification	>100ns	>0ns	>0.6us	>0.6us	>0.6us	>-0.5V
Measured Result	993.1ns	221.9ns	2.247us	1.071us	2.505us	-0.144V

Overshoot

Ring up

Ring down

Note

Specification

<VDD+0.5V

<5.56V

<0.3Vdd

<1.518V

>0.7Vdd

>3.542V

20~300ns

20*(VDD/5.5V)~300ns

18.4~300ns

I2C Fast Mode

Measured Result

5.264V

0.224V

4.88V

178.4ns

13.33ns

over 7 years ago

0 Koteshwar Rao over 7 years ago

TI__Guru 55795 points

Hi Jim,

Could you please confirm whether the above measurements mentioned are for Side1 of ISO1541 or for Side2?

I see that the fall time, tf, is coming out to be ~13ns and is outside the range of ~20 to 300ns. Do you know how did customer get the ~20 to 300ns range? Shouldn't it be better if tf is lower than the range specified?

The fall time can be increased by increasing the values of either pull-up resistor or the bus capacitance. Please make sure the max bus capacitance of 40pF and 400pF for Side1 and Side2 are not violated. Thanks.

Regards,
Koteshwar Rao

0 Koteshwar Rao over 6 years ago in reply to Koteshwar Rao

TI__Guru 55795 points

Hi Jim,

Please do let us know if the lower tf is still a concern to customer or if customer could increase it using external pull-up resistor? Thanks.

Regards,
Koteshwar Rao

Interface

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ISO1541: I2C Falling Time Fail