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Does a bq78PL114S12 "System Present" pin exist? Need to keep it out of Standby Mode

John M
Expert 2135 points
Other Parts Discussed in Thread: BQ78PL114

We have an application for the bq78PL114S12 that would only rarely have the pack connected to a SMBus host. To allow for Qrem updates (and any other learning) we want to keep the pack from going into Standby Mode (even though it would draw more current from the pack).

We were considering adding pullups to the SMBCLK and SMBDAT lines on the bq78PL114S12's PCB but noticed a reference to a "SYSTEM PRESENT pin" near the end of section 5.3 of the Technical Reference document.

Does this pin exist? We can't find any reference to it in any other documents. Or is this just a reference to the System Present FET Control bit and not a pin?

If it is just a reference to the System Present FET Control bit, which won't help us in this situation, can we add high-value pullups, let's say 100K, to the SMBCLK/SMBDAT lines to keep the chip out of Standby Mode? Right now there are 1M pulldowns on those lines on our bq78PL114S12 PCB. We'd use VLDO1 to do the pulling up...would that be a problem?

Lastly, what is the current draw for SMBCLK and SMBDAT pins when pulled up? We want to make sure that LDO2 isn't being asked to provide too much current.

  • 0
    TI__Intellectual 1940 points

    Your approach is correct except that SMBDAT and SMBCLK are 5V tolerant pins. So, connecting to VLDO2 would be a problem (> 5V w/respect to VSS). I suggest connecting to VLDO1 or cell 1. Per the datasheet, a minimum VOH on these pins is 2.1V. As far as a resistor value goes, I would consult the SMBus spec. and the bq78PL114 datasheet for values at different VDD.  We do comply with the +/-5uA leakage current rating that is specified in SMBus doc.

    Thanks for finding the mention of SYSTEM PRESENT pin in TRM. There is no SYSTEM PRESENT pin. This is a type-o. We only have the SYSTEM PRESENT function in firmware that is described in Section 5.2.2 of the SLUU330B doc.

  • 0 in reply to Jim M15252
    Expert 2135 points

    Ahh...forgot about VLDO2 riding atop Cell1. It had the higher current spec in the datasheet so I picked it. I'll use VLDO1 instead. And I'll take a peek at the SMBus specs, great idea.

    It seemed that the SYSTEM PRESENT pin mention was a typo. Really could have used something like that though. :-)

    Thanks!