LSF0108-Q1: Pull-up resistor selection

Arie Li

Part Number: LSF0108-Q1

Hi Experts,

LSF0108-Q1 datasheet listed some pull-up resistor values which are too small for customer to save the system power. Can customer use larger resistors such as 10kohms or 50kohms here? Is there any difference of the principle to select the pull-up resistor for output port A and output port B? Thank you.

over 4 years ago

0 Clemens Ladisch over 4 years ago

Guru 267950 points

The LSF itself does not impose an upper limit on the value of the pull-up resistors. However, the resistors and the parasitic capacitances in the circuit form an RC low-pass filter that limits the signal frequency.

For power saving, it might be a better idea to use a direction-controlled translator.

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

TI__Expert 3390 points

Hi Clemens,

Thanks for your reply. From my understanding, when the B-side is used as an output, large resistance would cause slower response which results in frequency limitation. When the A-side is used as an output, the high level of A-side follows B-side, so the pull-up resistor value will not affect the response speed so much, maybe it can use larger resistor such as 10k, am I right?

Arie

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

Guru 267950 points

Voltage-Level Translation With the LSF Family says:

During the weak 1 condition, TI recommends only high-impedance loads because very small amounts of current will cause the output voltage to drop significantly. Pullups to Vref_A are not required but allow heavier loads on the low side and help with signal integrity issues that may arise.

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LSF0108-Q1: Pull-up resistor selection