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[FAQ] TPS549D22: Can the PMBus circuits in the TPS549B22 / TPS549D22 support 1.8V pull-up termination voltage?

Peter James Miller
Guru 52945 points
Part Number: TPS549D22
Other Parts Discussed in Thread: TPS549B22,

Question:

Can the PMBus pins on the TPS549B22 and TPS549D22 support a 1.8V I/O termination voltage for the pull-up resistors?

Answer:

The TPS549B22 and TPS549D22's PMBus pins are designed to meet SMBus 3.1 "High Power" 1MHz class voltage and timing requirements.

This includes a Input Voltage "High" (VOH) maximum threadhold of 1.35V and Input Voltage "Low" (VIL) minimum of 0.8V in order to support 1.8V termination voltages and a maximum Output Voltage Low (VOL) of 0.4V with a 20mA pull-up.

The pull-up termination resistance should be sized to ensure the termination current with a 0.4V output is less than 20mA (no less than 70Ω) while ensuring a low enough rise-time to rise from 0V to 1.35V within the timing constraints of the bus-speed used and the total bus capacitance.