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BQ25703A: Dual TPS65988 plus BQ25703A schematic review request

oac
Prodigy 120 points
Part Number: BQ25703A
Other Parts Discussed in Thread: TPS65988, CSD17578Q3A, CSD87330Q3D

Hello, I would like to request a review of a couple of our schematic sections.

We have a 4 type C port design using two TPS65988DJRSHR and a single BQ25703A.


Could we please request the start of an offline or non public discussion to have a TI Engineer take a look at our design?

Thank You

  • 0
    TI__Mastermind 24075 points

    Hi oac,

       Please refer to this document to assist you in your schematic review: 

    Contains explanations for the different passive components required. The user guide is also a helpful resource. For the TPS65988 portion, please create a separate post with that part number in the title, and it will be assigned to the experts in charge of type-c products.

  • 0 in reply to Kedar Manishankar
    Prodigy 120 points

    Thank you.
    We will double check that we have followed the schematic checklist. The team may have already done that, but we will confirm now.

    We will leave this request open for now, and after we confirm the checklist, we will request a review again. Thank you.

    Regarding the PD controller, its circuit is i2c linked to the Charger so we assumed to include them in the same request but we are ok with submitting that request separately.


    Thanks

    OAC

  • 0 in reply to oac
    TI__Mastermind 24075 points

    Hi oac,

       Sorry for the inconvenience. We have separate teams in charge of the products so that team will have the experts for PD products, and we will be the experts for battery charger products. I will leave the thread open.

  • 0 in reply to Kedar Manishankar
    Prodigy 120 points

    No problem at all! I am fortunate to have your help anyway.

  • 0 in reply to oac
    Prodigy 120 points

    Ok, thanks, we have done the schematic review and have a few questions. Could we have comments on the following?

    1. C24 and C35 in our design is currently 33uF ceramic cap. The recommendation was 33uF tantalum. Because of space we used 1206 package ceramic. Ok? Or not?

    2. For HIDRV1, LODRV1, HIDRV2 and LODRV2 , recommended MOSFET is the CSD17578Q3A. We are using CSD87335Q3DT.

    3. CELL_BATPRESZ resistor divider is set for 2S battery(Our battery is 2S2P). So for setting ILIM_HIZ:

    Currently R16 is 150k and R15 is 100k. Which yields VILIM_HIZ To 2.4V.  And input current limit will be ~3500mA.

    Is this ok? We have option to change this from register setting also if required I guess as per datasheet.

    4. PSYS, typical value of 30.1k is used. PSYS ratio is programmable in register setting option also right?

    The battery we are using as as follows:

    www.rrc-ps.com/.../DS_RRC2057.pdf


    Thanks

    OAC,

  • 0 in reply to Kedar Manishankar
    Prodigy 120 points

    Ok, thanks, we have done the schematic review and have a few questions. Could we have comments on the following?

    1. C24 and C35 in our design is currently 33uF ceramic cap. The recommendation was 33uF tantalum. Because of space we used 1206 package ceramic. Ok? Or not?

    2. For HIDRV1, LODRV1, HIDRV2 and LODRV2 , recommended MOSFET is the CSD17578Q3A. We are using CSD87335Q3DT.

    3. CELL_BATPRESZ resistor divider is set for 2S battery(Our battery is 2S2P). So for setting ILIM_HIZ:

    Currently R16 is 150k and R15 is 100k. Which yields VILIM_HIZ To 2.4V.  And input current limit will be ~3500mA.

    Is this ok? We have option to change this from register setting also if required I guess as per datasheet.

    4. PSYS, typical value of 30.1k is used. PSYS ratio is programmable in register setting option also right?

    The battery we are using as as follows:

    www.rrc-ps.com/.../DS_RRC2057.pdf

    Thanks

    OAC,

  • 0 in reply to oac
    TI__Mastermind 24075 points

    Hi OAC,

    1. The reason tantalum is recommended, is to account for derating of ceramic capacitors with voltage. As long as the effective capacitance is in the valid range after accounting for derating, you will be fine
    2. CSD87335 has low RDSon for the LSFET which is good for reducing conduction loss, however the voltage sensed across the LSFET is used by our converter, so too low of an RDSOn on this FET could cause issues for sensing the dV across the FET. I would recommend choosing a FET with slightly higher RDSon (~8-10mohm) for the sync/LSFET.
    3. This should be fine. Host can always update input current limit later.
    4. Yes the KSYS ration can be programmed.

  • 0 in reply to Kedar Manishankar
    Prodigy 120 points

    Hello,

    Thank you! We had chosen the mosfet based on our size requirements.... as it is a small board..

    We need something 3.3mm x 3.3mm or smaller.

    Is CSD87330Q3D acceptable? (9.3-11mohm RDSon)

    Thanks!

  • 0 in reply to oac
    TI__Mastermind 24075 points

    Hi,

       This should be acceptable.