LSF0102-Q1: Size of pull up resistors

Kevin SHIN

Prodigy 495 points

Part Number: LSF0102-Q1

My customer used LSF0102-Q1 as a level shift.

Vref_A = 3.3V, Vref_B = 5V

They have some questions about using pull resistors.

1. Is it ok using 33kΩ as pull up resistor to B side for customer's IC requirement?

2. Is it possible using 10kΩ as pull up resistor to A side to decrease current consumption?(Is it ok not to use pull up resistors by applying table in LSF0102-Q1 datasheet 9.2.1.2.2?)

3. Does LSF0102-Q1 operate well using pull up resistor to Vref_B pin not 200 kΩ but 100 kΩ?

Thank you.

Best Regards,

Kevin Shin

over 5 years ago

0 Clemens Ladisch over 5 years ago

Guru 316690 points

1. The LSF itself does not require any specific pull-up resistor value. Larger pull-up resistors limit the possible speed (because with the parasitic capacitances in the circuit, they form a low-pass RC filter); smaller pull-up resistors consume more current and increase V_OL.

2. In general, you want pull-up resistors at all LSF outputs to improve signal integrity. See section 5.2 of Voltage-Level Translation With the LSF Family.

3. That resistor is not a pull-up resistor; its purpose is to limit the current that flows into Vref_B and out of Vref_A. Using 100 kΩ will increase this current, which should not have an adverse effect.

0 Dylan Hubbard over 5 years ago in reply to Clemens Ladisch

TI__Mastermind 45725 points

Hey Kevin,

I would also recommend watching these training videos on the LSF family: https://training.ti.com/node/1139264?context=1139264

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LSF0102-Q1: Size of pull up resistors