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BQ25120A: Regulator output

Dan Des57
Prodigy 220 points
Part Number: BQ25120A
Other Parts Discussed in Thread: BQ25121A

Hi there,

I am planning on using the BQ25120A for a wearable, battery powered application and had a few questions.

1. What are the default outputs of the two regulators? The buck I know is 1.8V but can I power my micro at startup from the LS/LDO pin at startup?

What is the LS/LDO startup default voltage?

2. Is it better to run my system off of a lower voltage if I can? For example, should I run all my devices at 1.8V (assuming they are capable of this)? Does this preserve power?

  • 0
    TI__Genius 12485 points

    Dan,

    Sure. The BQ25120A is good for wearable battery applications. 

    The default on the BQ25120A is 1.8V VSYS. There are also 2.5 VSYS and 1.2 VSYS for whichever is better for your application.

    The LS/LDO is a defaulted to loadswitch. Depending on how you wire LSCTRL or configure I2C, you can either get regulation for LDO options or just have it as a load switch. 

    For the LDO, yes using the lowest voltage is the best. If say you wanted 1.2V on LDO, I would recommend you connect VINLS to VSYS rather than PMID. Really depends on what voltage you are trying to get on the LDO. 

    regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 220 points
    Sorry. Can you clarify what are the options for the LS/LDO pin. Can I run my mcu at startup off of the LSLDO pin. How can I configure this?

    Also, I was questioning whether in general, its better to run the system at a lower voltage and not just the LDO.
  • 0 in reply to Dan Des57
    TI__Genius 12485 points
    Hi Dan,

    What is the voltage that your MCU needs for startup? It depends on your system Iq at different voltages. It is probably the best to run your MCU to VSYS (DC-DC) as the rails to communicate on I2C can also be pulled to the same voltage.

    Regards,
    Gautham
  • 0 in reply to Gautham
    Prodigy 220 points

    I was originally planning on running my MCU at 3V3 off of the LS/LDO pin. I'm starting to think this cannot be done at startup

    All of my other peripherals were going to run off of 1V8.

  • 0 in reply to Dan Des57
    TI__Genius 12485 points
    Dan,

    Yes. That would be hard to do as you would need to initialize the LDO before running it off to 3V3. Can your MCU take in 2.5V? I have the BQ25121A which can run at 2.5V on startup for the DC-DC.

    The rest of the peripherals can either be connected to the DC-DC (if they can tolerate that is) or connected to the LS/LDO. On boot, the MCU can initialize the LDO to start off with 1.8V to power the peripherals.

    Regards,
    Gautham
  • 0 in reply to Gautham
    Prodigy 220 points
    Actually, its fine. I can run my mcu off of 3V3 and then run some peripherals off of the LS/LDO
  • 0 in reply to Dan Des57
    TI__Genius 12485 points
    Sounds good. Let us know if you have any questions.