LSF0102-Q1: Pullup Resistor

Mingkang Song

Part Number: LSF0102-Q1
Other Parts Discussed in Thread: LSF0102, TXU0102-Q1

The pullup resistor requirement in the datasheet is as follows. Is the leakage current of the MCU already taken into account in this equation? Thanks!

6 months ago

0 Clemens Ladisch 6 months ago

Guru 259430 points

No, but the leakage current (a few µA at most) is insignificant compared to the pull-up current.

(The pull-up current is also limited by the drive strength of the MCU and the other devices; it is likely that you must use much less than 15 mA.)

0 Jack Guan 6 months ago

TI__Mastermind 20581 points

Hey Mingkang,

Clemens is correct here. The 15mA in this case only applies to the current flowing through the internal FET and does not take leakage into MCU into account:

Regards,

Jack

0 Mingkang Song 6 months ago in reply to Clemens Ladisch

TI__Prodigy 700 points

Thanks for your reply! The situation is that: The current at MCUGPIO is shown in the figure. If the LSF0102 is pulled low close to ground at this time, the MCU current is combined with the pull-up current to form the output. At this point, the output current at the MCU side is calculated to be MA level. May I ask if the LSF0102 can work at this time?

0 Clemens Ladisch 6 months ago in reply to Mingkang Song

Guru 259430 points

When the LSF input is connected to a push/pull output, you do not need a pull-up resistor. See section 5.2 of the Voltage-Level Translation With the LSF Family application report.

0 Jack Guan 6 months ago in reply to Mingkang Song

TI__Mastermind 20581 points

Hey Mingkang,

This should be acceptable as long as it is within the recommended range shown in the datasheet:

Regards,

Jack

0 Mingkang Song 6 months ago in reply to Clemens Ladisch

TI__Prodigy 700 points

Thanks for your reply! If this resistor is required, how do I calculate the value of this resistor?

Direction of level translation: SoC communicates bidirectionally with MCU
Amplitude: 3.3 V to 5 V.
Type of I/O on both sides: Pull push
Rate: 10M

0 Clemens Ladisch 6 months ago in reply to Mingkang Song

Guru 259430 points

Both the MOSI and /CS signals are unidirectional. For this application, you should use the TXU0102-Q1.

Are there any other signals that you are translating? Are you using SPI or QSPI?

0 Scarlett Cao 6 months ago in reply to Clemens Ladisch

TI__Expert 3490 points

Hi Clemens and Jack,

Thanks for your feedback. Since there's customer design, let's move to email thread.

Thanks

Scarlett

Logic

Logic forum

LSF0102-Q1: Pullup Resistor