Q
I work with the ADM1030 as thermal controller on a IIC bus. I noticed that the
IIC bus accepts lower pull-up resistors as Analog Device states as "typical"
for the ADM1030 in the data sheet. My question is know: what is the minimal
needed pull-up resistor on the SDA/SCL bus lines? Can a low value (1k Ohm)
produce a bus blocking?
A
The ADM1030 is designed for the SMBus rather than the IIC standard. They differ
in a few areas such as allowable supply voltage ranges etc.
The minimum pull up resistor value is defined by the current that can be sunk
by the output transistor and still maintain a valid logic low. The ADM1060 is
specified as sinking 6mA while keeping the voltage below 0.4V, so no problem to
place a 1k resistor as a pull up.
The maximum pull up resistor is defined by
a) combined leakage current (in a logic high state) of all components on the
bus - should not cause the voltage to drop out of the valid voltage range.
b) the bus capacitance and how long it takes for the bus to return to logic 1
when the bus is released.
The SMBus specification defines these values and the ADM1030 will be compatible
with them.
