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BQ25887EVM: BQ25887 EVM PMID pin

Babu Vishwanath Hemath Kumar
Prodigy 230 points
Part Number: BQ25887EVM
Other Parts Discussed in Thread: BQ25887

Hi, 

My name is Babu, 

Can you tell what is the exact use of PMID pin in EVM module, do we have to connect the battery to the PMID bin for charging the cells?

If not please let me know what is the power pin for charging the battery cells because in EVM module of BQ25887, my battery cells are not charging?

Please help me regarding this

  • 0
    TI__Genius 10745 points

    Hi Babu,

    The PMID pin represents the output pin of the Boost topology and is used to receive the current from the boost inductor to provide to the VBUS pin. We only recommend connecting the inductor and capacitor to this node as connecting input power to this pin would bypass the blocking FET which is an important safety feature.

    The points to which your battery cells should be connected are BAT, TOP-/BOT+, and GND pins. These can be connected to via J4 and J5 on the EVM. You can get a better idea on how to set up a battery or battery simulator and a voltage source on the EVM using the EVM user guide section 2.2.

    Please let me know if after reviewing the section you are still unable to initiate charging of your batteries.

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 230 points

    So, in PMID connection we have to give input supply, I will let you know if I still have problem.

    For PMID J3 do we have to connect the power supply to that pin too?

  • 0 in reply to Babu Vishwanath Hemath Kumar
    TI__Genius 10745 points

    Hi Babu,

    Input power supply should be connected to VBUS via J1. For the EVM nothing needs to be connected to PMID 

    Best Regards,

    Juan Ospina

  • 0 in reply to Juan Ospina
    Prodigy 230 points

    Thank you Juan,

    Can you tell me how we can control the QBLK mosfet in the EVM module?

    So if you see the inductor value used is same as compared to both EVM and my pcb design but the package model is different will it effect the input supply?

    What is the exact purpose of the inductor? Because in my designed pcb the current is not flowing inside the IC to charge the cells.

  • 0 in reply to Babu Vishwanath Hemath Kumar
    TI__Genius 10745 points

    Hi Babu,

    The purpose of the QBLK FET is to prevent current flowing from the battery to the VBUS pins. This is a safety feature to prevent possible shorts at the charging port. QBLK is controlled by the devices' internal controller. Once a power source is connected that is able to pass Poor Source Qualification (8.3.2.1 in the Datasheet) then the QBLK should be enabled allowing to current to flow from the power source to the boost converter.

    The inductor is essential to Boost converter operations. You can read more about the purpose of the inductor and boost converter theory here. So long as the inductor value is the same it should be functional, though it is important to keep in mind the charge rating and dc resistance values for your application.

    To help debug this issue, can you please provide the following values when you attempt to charge the cells:

    VBUS, VBAT, and VMID.

    Can you please provide a waveform of the SW node when you attempt to charge your cells?