LSF0108: pull high resistor for GPIO

Fred Cheng

Part Number: LSF0108

Hi team,

why there're still some pull high resistors in GPIO application, is it necessary?

unlike I2C, I thought the pull-high pull-low of GPIO are already integrated in the master .

if the pull high is needed , please provide me a solution that include the pull high resistor in IC.

thanks

0 Clemens Ladisch over 2 years ago

Guru 316440 points

Pull-up resistors might or might not be necessary, depending on the application.

The image does not show the LSF0108, and it does not show GPIOs.

Please specifiy how many signals you have, in each direction, the two voltages, and the data rate.

0 Fred Cheng over 2 years ago in reply to Clemens Ladisch

Hi Ladisch,

from this graph, I think the reason that GPIO still need external pull-high,

is only at higher VCC point and at signal receiver point .

for example , this red circle , we see the signal is from 1.8V to 3.3V.

since 1.8V can't generate 3.3V, so we still need extra pull-high

please help confirm

+1 Clemens Ladisch over 2 years ago in reply to Fred Cheng

Guru 316440 points

Yes, translating up is one of the cases where a pull-up is needed.

See section 5.2 of the LSF application note.

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