• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 2725 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25606: + LM5166 OTG mode

Thijs Sillen34
Intellectual 260 points
Part Number: BQ25606
Other Parts Discussed in Thread: LM5166, , LM2941

Hello,

I have a question about the BQ25606 in OTG mode in combination with the LM5166.

1. Is it correct that in OTG mode the "boost" voltage will be on the VBUS pin (VOTG in sch)?

2. Will this voltage also be on the SYS pins (VSYS in sch)?

3. If LM5166 (see sch) is disabled and the BQ25606 OTG is enabled. Will the LM5166 short it to ground or will it by default just keep the output (switch) floating ? / reverse blocking ?

The reason of doing is because EXT can be up to 40V and there is no off the shelf (cheap) charger that can handle this. That is why the LM5166 is before it.

The OTG "boost"  would be used to drive a GSM module when the external voltage is not applied. I just want to be sure that this combination of parts would not mess up things in that situation.

LM5166 block diagram:

  • 0
    TI__Mastermind 25800 points

    Hey Thijs,

    1) Yes, the VBUS voltage will be on the VBUS pin (VOTG in your schematic) when the charger is in boost mode. That is a 5V output.

    2) This voltage is not on the SYS pin (VSYS in your schematic). SYS only sees the battery voltage and is essentially the input voltage to the boost converter (starting before the inductor)

    3) The LM1566 has an integrated NMOS as the high-side switch, with a body diode that can be forward biased towards VIN (on the LM5166). From that, VBUS, when boosted in OTG mode on the charger, will appear across the inductor L2, and VIN will see a diode drop from that voltage, which could enable the converter (as you pulled it up through a 0 Ohm (R3). I am not sure what would happen here, but it could affect the regulation loop of the LM5166 as it would try to switch when enabled.

    My question to you: Are you powering the GSM module from the VSYS pin or the VOTG pin?

    Regards,

    Joel H

  • 0 in reply to Joel Hernandez II
    Intellectual 260 points

    This is what I made of it now. The idea is that D3 prevents the VOTG "boost" voltage going into the LM5166 circuit.

    LM2941 would only be enabled in the case that "EXT" is not plugged in. And BQ25606 OTG is on.

  • 0 in reply to Thijs Sillen34
    TI__Mastermind 25800 points

    Hey Thijs, 

    This looks fine. As you wrote in your design note, only set OTG high when EXT is not present. 

    In regards to your last comment about the LM2941 not being enabled unless EXT = 0 and OTG = HIGH. I assume this is done in software correct via the "4V5 EN" and "OTG-EN" signals, correct? My only thought would be to make sure that these signals have a fixed logic state when there is no software control. A common example of this is an open-drain output without a pull up on the node. OTG pin could float between node and falsely enable. 

    Regards,

    Joel H