SCPS272C October 2019 – January 2021 TCA9511A
PRODUCTION DATA
The system pull-up resistors must be strong enough to provide a positive slew rate of 1.25 V/µs on the SDA and SCL pins, in order to activate the boost pull-up currents during rising edges. Choose maximum resistor value using the formula given in Equation 1.
where R is the pull-up resistor value in Ω, VCC(MIN) is the minimum VCC voltage in volts, and C is the equivalent bus capacitance in picofarads (pF).
In addition, regardless of the bus capacitance, always choose RPU ≤ 65.7 kΩ for VCC = 5.5 V, RPU ≤ 45 kΩ for VCC = 3.3 V, and RPU ≤ 33 kΩ for VCC = 2.5 V. The start-up circuitry requires logic HIGH voltages on SDAOUT and SCLOUT to connect the backplane to the card, and these pull-up values are needed to overcome the pre-charge voltage.