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BQ25756E: Power sharing battery backup power circuit

Rik Imbens
Prodigy 10 points
Part Number: BQ25756E
Other Parts Discussed in Thread: BQ25622, BQ25622E, BQ25630, BQ24171, BQ24170, BQ24172

Dear Sir/Madam,
 
I hope this mail finds you well.
 
I have a question regarding the LFP battery charger ICs at TI.

I am currently designing a power circuit that has to compensate for short peak moments. The adapter used in the system is a 6 volts, 2.5 ampere adapter, but the system's peak power consumption is 25 watts. I would like to use an LFP battery to share power with the adapter and deliver that extra 10 watts of energy. Can you suggest a chip that has the capabilty of sharing power. The output voltage of the whole system should be 15 volts. If needed this can be done by adding a boost converter after the charger IC. I would like to set the current limit and output voltage without any programming or MCU connected to it.

So to sum up the requirements:
Input adapter: 6 V @ 2.5 A → 15 W max
Load peak: 25 W @ 15 V → ~1.67 A, Missing power: ~10 W at peak (~0.67 A at 15 V)
15 volts system voltage
No firmware (SMBus or I2C connection), setting all limits and voltages by resistor circuits.
1 LFP cell
 
Do you have a suggestion for which chips to use?
 
Thanks in advance.
 
Best regards,
Rik Imbens
+31 6 27 38 69 22
  • 0
    TI__Expert 8670 points

    Hi Rik,

    Let me see if I understand this requirement correctly.

    Does this block diagram look right?

    Best regards,
    Michael

  • 0
    Prodigy 10 points

    Dear Michael,

    Thank you for your prompt response.

    Yes, indeed, for this project it is important that the SYS rail can be powered by both the battery and adapter where the battery supplies the extra power needed where the adapter is limited by the charger component. I would like to set the limit of the adapter by a resistor network.

    Does TI have a chip that offers this functionality?

    Thank in advance.

    Best regards,
    Rik Imbens
  • 0 in reply to Rik Imbens
    TI__Expert 8670 points

    Hi Rik,

    I would recommend the BQ25622E. This is a version of the BQ25622 with fewer features and a lower current, but we still have the ILIM pin that can limit the current of the adapter. I2C would be needed to control other features of the chip (such as charge voltage and charge current).

    We also have a new part BQ25630 that may be worth looking at if you have the timeline for it.

    Do these parts work for your system? I can also suggest a fully standalone option if necessary.

    Best regards,
    Michael

  • 0 in reply to Michael Bradbourne
    Prodigy 10 points

    Dear Michael,

    Thank you for your prompt response.

    These parts have to be controlled by a host communicating over I2C.

    I would like to have a standalone option instead.

    Thank in advance.

    Best regards,
    Rik Imbens
  • 0 in reply to Rik Imbens
    TI__Expert 8670 points

    Hi Rik,

    How does the BQ2417x family of buck charging devices work for you? The BQ24170 is 4.2 V/cell standalone. The BQ24172 has adjustable battery voltage. The BQ24171 has adjustable battery voltage and JEITA.

    Best regards,
    Michael Bradbourne