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BQ24780S: BQ24780S：3 Questions about BQ24780S

user6364061
Prodigy 40 points
Part Number: BQ24780S
Other Parts Discussed in Thread: BQ24703, , BQ24800, BQ25710, BQ25700, BQ25703, BQ25713

 

We are in designning type C PD charger systems with sink role. Input voltage 5~20V, battery is 3s (full at 13.2V). We want to use a charger ic to charge the battery and also suplly the system in the same time. If the outside adapter power is not enough for the system demand, we will use both the adapter and battery to supply the vsys all the time until the battery is empty.

1. So I think I should use a buck-boost charger ic like bq24703/bq24700. Is it correct to use bq24780s? I see it is just a boost charger?

2. what is the voltage of VSYS. As in the spec，there is just a resister between vbus and vsys, not a inductance. So if the vsys equals to vbus, instead of a value I can specify like 13.2V ? What will happen if the adapter power is not enough, we want to use adpater and battery in the same time , suppose the vbat is 5V, vbat is 12V, what will happen?  what does "hybrid power boost mode" mean? just temporary support using adapter and battery together？

  • 0
    TI__Expert 5330 points

    Hi,

    It is possible to use BQ24780S (or the newer BQ24800) in a USB PD system, but since it only does buck charging, you would only be able to use adapters of 15V or 20V (or a nonstandard voltage over 15V) since you have a 3S battery.  Also, since the ACDET needs to be set to a value higher than the battery voltage, the ACFET won't even turn on if the adapter is less than 15V, which means that you not only can't use a smaller adapter to charge the battery, but you wouldn't be able to power the system either.

    The VSYS voltage is always the same as the adapter (i.e. VBUS) voltage.  Hybrid power boost mode will operate the converter in a boost configuration in order to supplement the adapter with the battery.  If you have 15V adapter and 13V battery, the 13V battery will be boosted up to 15V in order to supply the system at 15V from adapter and battery simultaneously.

    As long as the limitation of only supporting 15V and 20V adapters is okay (and not having any OTG / sourcing support), then BQ24780S will work.  If you want to be able to also run off of 5V and 9V adapters, or any non-standard adapter below 15V, they you would need a buck-boost architecture such as the BQ25710/3.  This can charge the battery from any adapter voltage.  And if you were ever interested in sourcing, it can generate any OTG voltage from 5V-20V from any battery voltage.  Because of these extra features, most people who are using USB PD end up selecting the BQ25710/3.

    Regards,

    Steve  

  • 0 in reply to Steve Preissig
    Prodigy 40 points

    Thank you, Steve

    I think I will choose BQ25710/3. What are the main differences among BQ25710 , BQ25703 and BQ25700 ? I see the cost are a little bit different. I want to choose a cost effective chip. When our equipment acts as a source, it just drive a portable hard disk or a U disk. So the output voltage/current is 5V/1.5A. So if used with a PD protocal chip , charger ic if with an OTG feature, there is no need for 2 power paths,  only a power path is enough.

    For example, if PD chip is bq65973d, only the   
  • 0 in reply to user6364061
    Prodigy 40 points

    Sorry,  the infomation is not enough. Only the upper MOS is connected and powerpath is 2 ways. If choose other pd controller without 2 internal power paths, only 1 external power path is enough. Are there some reference schematic for charger ic with OTG cooperated with PD controller? 

  • 0 in reply to user6364061
    TI__Expert 5330 points

    Hi,

    The BQ25710/13 are the next-generation BQ25700/03.  The versions ending in "3" have an I2C interface, whereas the versions ending in "0" have SMBUS interface.  Otherwise they are the same.

    This PD reference design uses BQ25713:

    https://www.ti.com/tool/PMP40441

    Also, you might be interested in this DRP reference design, which uses BQ25

    https://www.ti.com/tool/PMP4496

    Regards,

    Steve