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MCT8315A: Buck components deleted

Lien Tori
Prodigy 60 points
Part Number: MCT8315A
Other Parts Discussed in Thread: MCF8315C

Tool/software:

Hi

I am using the MCT8315A for a application that tends to be as small as possible, and I have another 3.3 power source.

Can the buck components be eliminated?  I want to reach minimum component count.

I tested it with the EVM, unsoldering Rbk, and not placing any Lbk, and connecting 3.3V to Vbk.

I set BUCK_SEL to 3.3V, and everithing is working well, but nothing says in the datasheet about this configuration.

I would like to know if something is missing, or it is ok to use like this

Thanks in advance

  • +1
    TI__Mastermind 23990 points

    Hi Lien,

    It is ok to not populate any of the buck components. When this is done you should set BUCK_SEL to 00b (3.3V) and short SW_BK and FB_BK to the external 3.3V source (which you have already done).

    What you have for the buck settings and layout/schematic for the buck pins is ok and it is fine to use the MCT8315A in this configuration.

    Regards,

    Joshua

  • 0
    Prodigy 40 points

    Hi Joshua, 

    Thanks for your answer. If we configure the HW as Lien says, is it safe to power the system given the MCT will by default try to regulate 5 V (considering it has not yet been programmed)?

    Best, 

    Nicolás

  • 0 in reply to Nicolás Barabino
    TI__Mastermind 23990 points

    Hi Nicolás,

    Please allow me sometime to check this out in the lab. I want to make sure that the device can be programmed while a buck undervoltage fault is occurring. I will aim to get back to you by next Tuesday.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    TI__Mastermind 23990 points

    Hi Nicolás,

    So long as the FB_BK pin has a voltage greater than 3.3V the MCT8315A is able to be programmed.

    It is ok to use the MCT8315A in the HW configuration mentioned by Lien and, so long as an external voltage is provided to the FB_BK pin, the device can operated as normal. The only difference could be the device reporting a BUCK_UV fault but this will not impact the MCT8315A's ability to drive a motor.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    Prodigy 60 points

    Thanks for your answer Joshua

    I have two more questions.

    • Is there any issue if the 3.3V goes up 1 sec after the main power? Because in some cases we are experimenting that, and the MCT doesn´t answer
    • Has the MCF version (8315 and 8316) the same hardware and the same behaviour of the buck? To considering the upgrade.

    Thanks again

  • 0 in reply to Lien Tori
    TI__Mastermind 23990 points

    Hi Lien,

    Lien Tori said:
    Is there any issue if the 3.3V goes up 1 sec after the main power? Because in some cases we are experimenting that, and the MCT doesn´t answer

    If this 3.3V source is being used to pull up FG and nFAULT, then the 3.3V coming up after VM is on can lead to the device getting into test mode which disables I2C communication. When using an external power supply for the pull-ups on FG and nFAULT we recommend having this supply come up before VM.

    Lien Tori said:
    Has the MCF version (8315 and 8316) the same hardware and the same behaviour of the buck? To considering the upgrade.

    There is a minor difference with 8315 the buck, the MCF8315C device has the option to disable the buck instead of it being left on. We also have a app note which does discuss operating the MCF8316C and MCF8315C without the buck and has an example schematic+layout: https://www.ti.com/lit/an/slla643/slla643.pdf

    We recommend using the MCF8315C or MCF8316C since these parts have a more updated firmware and additional features over their the A versions but function the same as their counter parts. Below is a PDF which covers the difference between the 8315 and 8316 and their different firmware variants: 

    6761.MCF8316_5A_Vs_C.pptx

     Regards,

    Joshua