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TPS65218: Application for Sitara AM3351 and Li-Ion battery with BQ25601 charger or similar

Daniel Brown
Intellectual 870 points
Part Number: TPS65218
Other Parts Discussed in Thread: BQ25601, AM3351, TPS65910, TPS650250, TPS65217

I need some help finding a part solution for my application which is the following:

Computer chipset: Sitara AM3351 with DDR and eMMC:
Currently using TPS65217C to provide regulated voltages

Board VIN = 5V

I am adding a Li-Ion battery to the system and need a way to charge it and manage it (hopefully, using
the TPS65217C already design in). However, I discovered I will need Icharge = 2A or more.

Vbat-max = 4.2V
Vbat-min = 3V

So, I thought I might add the BQ25601 to charge the battery and manage the powerpath. However, I planned
to take the Vsys of the BQ25601 and tie it to VAC of the TPS65217C. And this will NOT work, I think, because the
regulated Vsys voltage around 3.65V of the BQ25601 is below the turn on voltage of the VAC input. 

Should I change the way I think about using these parts? Should I use a different battery charge chip? Should
I use a different PMIC?

I started this post on the Battery charger forum but was directed here for a more suitable PMIC for my solution.

So far, I have found the TPS65218 might work.

I was looking at other PMICs that were designed for the Sitara series. The TPS650250 looked good for the low input voltage operation but it
does not have built in sequencing. The TPS65218 looks similar to the TPS65217 and does seem to have the low input voltage operation and
sequencing. Might the TPS65218 be a possible PMIC replacement? 

If so, can this chip be used with the BQ25601 in the way I was suggesting, take the Vsys powerpath output of the BQ25601
and tie to IN_BIAS and other IN_X inputs of the TPS65218?

  • 0
    TI__Expert 4155 points
    Daniel,

    What are your voltage, current, and sequencing requirements?

    You are correct that the BQ25601 should be able to power the TPS65218 due to it's lower minimum input voltages. The TPS65910 and TPS650250 might be worth looking into as well if you are looking at changing the PMIC. However, I am not sure what the voltage requirements are for the AM3351 so switching PMICs might be a little bit more difficult.

    I just talked to our TPS65217 device expert and he said you could power the TPS65217 through the BAT pin instead of the AC or USB pins. I think that might be your best option. Just make sure if you do that to not connect anything to the AC or USB pins as to avoid having 2 chargers trying to charge the battery at the same time.

    You could also forget the BQ25601 and just charge the battery off of the TPS65217 but you won't get 2A of charge current from that so it would take longer to charge.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Intellectual 870 points
    Voltage and Current requirements are primarily those of the AM335x chipset and those above:

    Board VIN = 5V

    I am adding a Li-Ion battery to the system and need a way to charge it and manage it (hopefully, using
    the TPS65217C already design in). However, I discovered I will need Icharge = 2A or more.

    Vbat-max = 4.2V
    Vbat-min = 3V

    Sequencing Requirements are those the AM335x, that is why I am looking at PMICs associated with Sitara.

    I DO require the Icharge = 2A minimum.

    I looked at TPS650250 but it does not have the sequencing. TPS65910 too many pins, too big (physically) and too complicated.

    Using the BAT pin of the TPS65217 seems to also be a way to go.

    The TPS65218 seemed to have all the necessary elements to be a replacement for the TPS65217. Can you confirm?
  • 0 in reply to Daniel Brown
    TI__Expert 4155 points
    Daniel,

    Yes it can be used to replace the TPS65217. Please refer to this user's guide to see how to use the TPS65218 to power an AM335x.

    www.ti.com/.../slvuaa9a.pdf

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Intellectual 870 points

    Nick,

    If I do decide to power the system through the BAT pins of TPS65217 as shown here from app note SLVA901, why does the suggested schematic not take the output SYS
    to the inputs of the LDOs and DCDCs as is normally the case? Are both options acceptable?

  • 0 in reply to Daniel Brown
    TI__Expert 4155 points
    Daniel,

    I am not sure why this schematic uses VIN for the inputs instead of SYS. I have notified our device expert for the TPS65217 so he can help answer your question.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    TI__Mastermind 30310 points

    Daniel,

    Solution circuit #1 is an adaptation of the circuit on page 77 of the TPS65217 datasheet, on the right-hand side of Figure 56.

    If there is only 1 form of power being used to operate the PMIC, where this source is NOT a battery and <5V, then the Power Path is unnecessary. As a result, all downstream rails (DC-DCs and LDOs) would be better off accepting power directly from VIN.

    This is an ideal workaround to avoid issues that some customers experience when using the Power Path without a battery. The schematic is usually copied from the Beagle Bone Black reference design and the PMIC is left as-is, and the lack of close examination of the PMIC schematic often leads to the lock-up.