LSF0102: about pull-up resistor

Joyce Li

Part Number: LSF0102

Hi dear expert,

I have a question related to the max pull up resistor value.

I have watched the training video, and it says: The pull-up resistors are always required on the high side, and pull-ups are only required on the low side if the low side device's output is open drain or its input has a leakage greater than 1 microamp.

So if the leakage current is 15uA, what is the max pull up resistor on the low side we could choose?

thanks a lot for your reply in advance.

Joyce

over 4 years ago

0 Dylan Hubbard over 4 years ago

TI__Mastermind 47735 points

Hey Joyce,

MDIO is open-drain if i'm not mistaken which is why you will need R1 to drive High. As for the value, the Up-translation video discusses how to calculate this for your desired data rate.

0 Joyce Li over 4 years ago in reply to Dylan Hubbard

TI__Intellectual 2170 points

hi Dylan,

I didn't see the maximum value for the R1, would you please specify?

thanks.

0 Dylan Hubbard over 4 years ago in reply to Joyce Li

TI__Mastermind 47735 points

Hi Joyce,

This equation:

I recommend re-watching this video, as it covers how the resistor size is related to the rise time thus related to data rate.

0 Joyce Li over 4 years ago in reply to Dylan Hubbard

TI__Intellectual 2170 points

Hi Dylan,

thanks for your reply. Sorry, still confusing, in my application, we are asking the *low side* pull up resistor max value, in the snapshot, B side is the high side, so RB1 and CB1 is related to the max data rate. how about low side RA1 max value restriction?

0 Clemens Ladisch over 4 years ago in reply to Joyce Li

Guru 324920 points

You can use the same equation with R_A and C_A for signals driven by the A device.

Logic

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LSF0102: about pull-up resistor