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BQ25890 – Disabling SYS output boosting

Laurence Parkins44
Prodigy 30 points
Other Parts Discussed in Thread: BQ25890, BQ25895, BQ25980

We are designing a USB power pack to be charged from a standard USB charger.

My idea is to have a boost converter and the relevant USB port controller on the output of SYS (rather than PMID as is usually suggested). This is to allow a device to charge while the pack battery is charging (on the assumption that SYS has priority of power over the charge circuit)

My question is: Is it possible to disable to boost function of SYS so that the boost converter doesn't kick in when battery voltage drops below SYSmin? As mentioned, we plan to use a TPS61230DRCT 5V boost converter to supply the downstream USB port so it seems pointless to have two boost converters acting.

If this is possible, what will the behaviour of the BQ25890 be when VBUS is being supplied by a wall charger?

Kind regards,

Laurence

  • 0
    TI__Guru**** 165886 points
    The bq25890 (as opposed to the bq25895 power bank part) does not automatically turn on the boost converter when VBUS is removed. The boost operation turns on 30 ms following OTG pin going HIGH and/or OTG_CONFIG bit written to 1 (default 0) if:
    1. BAT above BATLOWV
    2. VBUS less than BAT+VSLEEP (in sleep mode) - i.e. if VBUS is powered, OTG mode cannot be enabled.
    3. Voltage at TS (thermistor) pin is within range configured by Boost Mode Temperature Monitor as configured by BHOT and BCOLD bits.
  • 0 in reply to Jeff F
    Prodigy 30 points
    Thank you for the prompt response!

    That's good for my application I think. So with OTG off, the SYS output is permanently connected to the battery through BATFET? And what about when VBUS is connected?
  • 0 in reply to Laurence Parkins44
    TI__Guru**** 165886 points
    Yes, SYS output is connected to the battery through the internal BATFET all the time (VBUS attached or not) for discharge and as controlled by CE in or bit for charging when VBUS is attached. There is also a bit to turn off the BATFET for ship mode.
  • 0 in reply to Jeff F
    Prodigy 30 points
    Thanks again for your response. I have a couple of further questions to cement my understanding.

    Does the BQ25980 adjust charging times for the battery to compensate for the current draw from SYS through BATFET?

    I assume also that the voltage seen on SYS during the CV stage of charging will be 4.2V - (I(FET)*R(ON))?
  • 0 in reply to Laurence Parkins44
    TI__Guru**** 165886 points
    If the charger device is in DPM regulation or thermal regulation during charging, the charging current can be less than the programmed value. In this case, termination is temporarily disabled and the charging safety timer is counted at half the clock rate.

    In CV when charging, V(SYS) = V(BAT) + ICHRG*RDSON. When not charging, V(SYS) = V(BAT)+50mV if V(BAT) > VMINSYS or V(BAT)+150mV if V(BAT) <VMINSYS.