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BQ24618: Choosing Li-Ion charger and buck/boost converter for space restricted application

Wolfgang Wendnagel
Prodigy 30 points
Part Number: BQ24618
Other Parts Discussed in Thread: LM25118, , BQ24610, BQ25713, BQ25792, TPS25750, BQ25731

Hi,

For our application we have 5 to 28 V input (some users may use it with a USB Charger or powerbank, some users may use it from a 12-14V or 24-28V supply). It shall charge a Li-Ion battery (at least 2 cells in parallel). Furthermore the system load is going to be at 5V @ max. 3A.

The space on the pcb is limited to approximatedy 30x30 mm.

What is the approximate efficiency of the LM25118 when powered from a 3.7V Li-Ion battery with 5V output?

I thought about using the BQ24618 or the BQ24610 for charging and the LM25118 for buck/boost converter for the system load. Is this a reasonable choice? What is the difference between the BQ24618 and the BQ24610 apart from one tolerating also 4.7V?

What happens with the BQ2461x if the absolute maximum rating as reached or a little bit exceeded? In the datasheet there are two MOSFETS which could be used to disconnect from the input. Will it automatically disconnect from the input and switch over to battery power in such cases? Sometimes (e.g. if throttle is applied when using an alternator) the input may raise to the absolute maximum (or even a little bit higher) for short periods of time (a few seconds). However this should be a rare case.

When a user uses USB as a power source I could imagine that powering the system and charging the battery is too much for most sources (at 5V the user might end up needing 5A which is a little bit much). Is there a simple way to enable USB-PD for higher voltages and higher power (given the supply supports this)?

  • +1
    TI__Mastermind 40305 points

    Hello,

    For the efficiency of the LM25118 you need to post in a separate forum for that part.

    The comparison table in the datasheet shows the only major difference is the 4.7 V input like you stated. Please keep in mind however, both chargers are buck controllers and that you need headroom between your input voltage and output voltage for the battery to fully charge.

    We do not guarantee the behavior of the part if you exceed the absolute maximum rating. However, there is an ACOV voltage threshold of 32 V for BQ24618 and BQ24610. "Once the adapter voltage reaches the ACOV threshold, charge is disabled and the system is switched to the battery instead of the adapter."

    You would need to use a PD controller to negotiate the higher currents and voltages. I have not used our PD controller, the TPS25750, in conjunction with a battery charger other than the BQ25792, BQ25713, and the BQ25731. You would need to use it in sink only mode and make sure that the IINDPM of the charger is less than the negotiated contract current as well as configure the GPIOs properly to enable charge.

    Thanks,

    Mike Emanuel

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