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BQ2419x/BQ2429x application question: boost mode output pin

Zhiyong Li
Prodigy 180 points
Other Parts Discussed in Thread: BQ24297, BQ24295, BQ24195L, BQ24190, BQ24195, BQ24192, BQ24193, BQ24196

Hi,

I am working on an application that uses one Li-Ion battery as backup power and outputs two rails: 3.3v and 4.0v. BQ2419x/2429x seem quite a good fit. When I went through datasheets and user guides, I got a little confused about the output pin of 5v in boost mode.

I assume the output pin of 5v is VBUS when AC adapter is unplugged and boost mode is turned on. But according to the user guide (http://www.ti.com/lit/ug/sluua14c/sluua14c.pdf), a load( 10 ohm resistor) was installed between PMID and GND when boost mode was being tested. Does this mean that mean PMID is right output for 5V?

Please advise. Many thanks.

ZL

  • 0
    TI__Intellectual 1910 points

    The 5v boost output for bq24295 is at PMID output. For output at vbus, please consider bq24297. BTW, what is the boost output requirement? The bq24295/6 is capable of up to 1.5a output. We also have other device that can output higher power.

  • 0 in reply to SamW2000
    Prodigy 180 points

    SamW2000 said:

    The 5v boost output for bq24295 is at PMID output. For output at vbus, please consider bq24297. BTW, what is the boost output requirement? The bq24295/6 is capable of up to 1.5a output. We also have other device that can output higher power.

    Hi SamW2000,

    Thanks for confirming the output pin of 24295/6/7. Could you also talk about 2419x? At this point, I tend to use BQ29193 because of the unavailability of BQ2429x.  The boost output runs at average 300mA with peak at 1A. I believe 2419x can easily handle.

    According to block diagram, there is only one invert-blocking FET between PMID and VBUS, does that mean if such invert-block is not necessary, I can connect to either pin for boost output?

  • 0 in reply to Zhiyong Li
    TI__Intellectual 1910 points

    Zhiyong,

    The bq24195 (2.1A boost output) and bq24195L (1A boost output) are also suitable for your application described. It provides boost output at PMID. However, it would require a front end circuit at VBUS as described in the datasheet. If you only want boost output at VBUS, then any bq24190/2/3/6 device should work, they all have boost output of 1.3A. The following are the difference between their family members:

    bq24190: 4.5A charger with D+/D- interface

    bq24192: 4.5A charger with PSEL interface

    bq24193: 4.5A charger with PSEL interface and JEITA temperature

    bq24196: 2.5A charger with PSEL interface

  • 0 in reply to SamW2000
    Prodigy 180 points

    SamW2000 said:

    Zhiyong,

    The bq24195 (2.1A boost output) and bq24195L (1A boost output) are also suitable for your application described. It provides boost output at PMID. However, it would require a front end circuit at VBUS as described in the datasheet. If you only want boost output at VBUS, then any bq24190/2/3/6 device should work, they all have boost output of 1.3A. The following are the difference between their family members:

    bq24190: 4.5A charger with D+/D- interface

    bq24192: 4.5A charger with PSEL interface

    bq24193: 4.5A charger with PSEL interface and JEITA temperature

    bq24196: 2.5A charger with PSEL interface

    Hi SamW2000,

    Thanks for the nice summary about the difference. As a matter of fact I already decided to use bq24193 because I can save one thermistor and it is readily available.

    Back to my question regarding output pins of boost mode, here is my summary:

    For BQ24195 and BQ24295, use PMID as output in boost mode. This is clearly stated and demonstrated in typical application diagram.

    For bq24190/2/3/6, either VBUS or PMID can be used. Your post and datasheets tend to suggest VBUS, while user guide   SLUUA14C used PMID. Btw, that is why I got confused.

    My understanding is that for all BQ24x9x, VBUS and PMID pins are internally connected through a FET according to block diagram. except the invert blocking and a small voltage drop across that FET, there would be no difference between PMID and VBUS. In either boost mode or when AC adapter is plugged in, the voltage at PMID and VBUS is pretty much the same.

    Please correct me if I am wrong on this. Forgive me if this is a dumb request for clarification. I just want avoid any possible misunderstanding. As you may understand, any design mistake will result in cost and project delay which I could not afford at this point.

  • 0 in reply to Zhiyong Li
    TI__Intellectual 1910 points

    It is correct to think that both VBUS and PMID hav ehte same voltage when in either boost mode or adapter is plugged-in. For bq24190/2/3/6, in general it is used for USB On-the-Go and the USB connector is shared by the charger voltage input and boost out. For most design, the host would know to stop boost output at VBUS when cable is unplug-in before an adapter plug-in. If PMID output is used for boost, we would recommend similar front end circuit as shown in bq24195 datasheet application diagram. This is to ensure, boost mode is disabled when USB adapter is plugged-in.