Rainbow Electronics MAX7502 - Manual (Page 11)

Applications Information
Digital Noise
The MAX7500/MAX7501/MAX7502 feature an integrat-
ed lowpass filter on both the SCL and the SDA digital
lines to mitigate the effects of bus noise. Although this
filtering makes communication robust in noisy environ-
ments, good layout practices are always recommend-
ed. Minimize noise coupling by keeping digital traces
away from switching power supplies. Ensure that digital
lines containing high-speed data communications
cross at right angles to the SDA and SCL lines.
Excessive noise coupling into the SDA and SCL lines
on the MAX7500/MAX7501/MAX7502—specifically
noise with amplitude greater than 400mV
P-P (the
MAX7500/MAX7501/MAX7502s’ typical hysteresis),
overshoot greater than 300mV above +V
S
, and under-
shoot more than 300mV below GND—may prevent suc-
cessful serial communication. Serial bus no-acknowl-
edge is the most common symptom, causing unneces-
sary traffic on the bus.
Care must be taken to ensure proper termination within
a system with long PC board traces or multiple parts on
the bus. Resistance can be added in series with the
SDA and SCL lines to further help filter noise and ring-
ing. If it proves to be necessary, a 5k
Ω resistor should
be placed in series with the SCL line, placed as close
as possible to SCL. This 5k
Ω resistor, with the 5pF to
10pF stray capacitance of the MAX7500/MAX7501/
MAX7502 provide a 6MHz to 12MHz lowpass filter,
which is sufficient filtering in most cases.
Chip Information
TRANSISTOR COUNT: 9611
PROCESS: CMOS
MAX7500/MAX7501/MAX7502
Digital Temperature Sensors and Thermal
Watchdog with Bus Lockup Protection
______________________________________________________________________________________ 11