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MSP430FR5870: I2C Pull up resistance capable consist value

Part Number: MSP430FR5870

Hi Champs,

We are evaluating MSP430FR58xx I2C.

When they would like to use this clock rate 100KHz and set SCL and SDA of pull up resistance to higher value for reduce power consumption.

They tried to set  20Kohm. but, clock was not working. If they set 10kohm , clock is working normally.

There is no data sheet infromation for I2C pullup resister constant value. Which value is the most recommend value for MSP430FR58xx ?

Regards,

Kz777

  • Unfortunately there is no "best" value for I²C pull-up resistor because it depends on the individual application. The number of connected slaves is one of the most important things because each slave adds capacitance that will decrease the sharpness of the rising edge of SCL or SDA. The frequency is the other very important thing, of course. It is like asking for the required diameter of a water pipe when no one knows how many houses will be sourced from it. Here is an application report that might be interesting for you. If you want maximum power saving, the best way is having a look at the scope while changing the value for the pull-up resistors.

  • If 10 kΩ is the largest value that works in your tests, then you should reduce it further to 5 kΩ to have a safety factor.

    Consider reducing the clock rate instead. (Please note that the I²C bus consumes power only when a signal is low, so halving the speed and halving the resistor values increases power usage by the same factor. However, slower signals reduce EMI/EMC problems.)

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