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RF430CL330H pull up resistor

Stella Laksono
Intellectual 580 points
Other Parts Discussed in Thread: RF430CL330H

Dear all, 
I am having an RF430CL330H NFC Dynamic Tag Target Board in my hand now, 
and i am going to connect it with the microcontroller of a ventilation device through I2C connection. 

I have a question about the pull up resistor, 
So, in my own device, it has already a pull up resistor as much as 5K6,

and I noticed that on the RF430CL330H target board itself, it has already 4K7 pull up resistor, 

I wonder if i connect them, won't it be matter?
Or should i remove the pull up resistor either from the target board or my ventilation device?

Sorry, I am actually embarrassed to ask a basic question
But I do not want fail my project too because of my false assumption or wrong reference...

Stella 

  • 0
    TI__Guru* 91086 points

    Stella - 

    I2C spec states Rmin (when operating above 100kHz) is = Vcc - Vol / Iol, in this case, we have 3.3V - 0.4V / 3mA, which results in Rmin = 966 Ohms (lets call it 1k)

    so if there are 4.7k and 5.6k pullups (on each line) are in parallel, you will have equivalent of 2.5k Ohm pullup, which is above the Rmin, according to the spec.  

    Rmax is determined by the bus capacitance. 

    I think you will be fine, but to save a few fractions of a penny or euro, you could avoid the extra component on each line.

    for reference, check out page 55 of the spec ==> http://www.nxp.com/documents/user_manual/UM10204.pdf