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

MAX7500/MAX7501/MAX7502s’ typical hysteresis),

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

Digital Temperature Sensors and Thermal

Watchdog with Bus Lockup Protection

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