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TPS61086: for Dual Li-ion Battery input

tateo yamashiro
Guru 10890 points
Part Number: TPS61086
Other Parts Discussed in Thread: TPS61087, TPS61178

Hi,

We got a question from customer about TPS61086.
Could you help us?

[Question]
Our customer is considering to use TPS61086 for Dual Li-ion battery input. So they are considering to separate VIN from power stage. Please see below figure.

 - Is there any concerns about this usage?
 - If the IC can accept this usage, is there any sequence requirements between IN, EN, MODE and SW?

Best Regards,
tateo

  • 0
    TI__Mastermind 40080 points

    Yes, the power Vin and the control Vin can be seperated.

    The sequence: Apply VIN to the TPS61086 first, then apply the input power to power stage (inductor), finally enable the IC by pulling EN pin high

  • 0 in reply to Helen chen
    Guru 10890 points

    Hi, Thank you for your support.
    Regarding your suggestion, I think they need high side SW in battery Line. If they apply to power stage first, then apply VIN, what kind of concerns might be occurred?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 40080 points

    As their input voltage is low: 6-8.4V, so it should be OK to add the Power Vin first.  If the input voltage is higher, like higher than 10V, the IC's low side FET maybe mistriggered because of the dv/dt.

    The sequence I suggested to you is the best choice, but not a must. But be sure  "EN"  the IC after both the power Vin and control Vin ready.

  • 0 in reply to Helen chen
    Guru 10890 points

    Hi, It's been a long time. We got additional question. Could you help us?

    - They are considerting to use TPS61087 in the same way as TPS61086. Is there any concerns about this usage?

    - In abnormal situation, loss of power supply occurs while the IC is under operation. Is there any possibility the IC(TPS61086, TPS61087) will be damaged in this condition?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 46905 points
    We'll check if the TPS61087 is also OK. before that, could you check if TPS61178 is good for your application?
  • 0 in reply to Jasper Li
    Guru 10890 points

    Hi, Thank you for your reply. TPS61178 is not good for their application. Because it can't meet their target price. Please let me know if you get the feedback about TPS61087.

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 46905 points
    The device can operates at separated input voltage, but the switching frequency will become much higher as battery voltage is much higher than VIN voltage. because this device senses the VIN and output voltage to calculate the OFF time. so i would suggest power the VIN with 6V instead of 3.3V
  • 0 in reply to tateo yamashiro
    TI__Mastermind 40080 points

    Hi Tateo-San,

    Sorry, I was out of office recently and just come back.

    TPS61087 can also used in this application. the main difference between TPS61087 and TPS61086 is that tps61086 has mode seleciton function while tps61087  doesn't have. and TPS61087 has higher current capability.

  • 0 in reply to Helen chen
    Guru 10890 points

    Hi, Thank you for your reply. If SW is separated from VIN and VIN is much lower than SW, switching frequency of TPS61086 and TPS61087 will become much higher. Is my understanding correct?

    And please give us your feedback about below question.

    - In abnormal situation, loss of power supply occurs while the IC is under operation. Is there any possibility the IC will be damaged in this condition?

    Best Regards,
    tateo

  • 0 in reply to tateo yamashiro
    TI__Mastermind 40080 points

    Hi Tateo,

    In abnormal situation, loss of power supply occurs while the IC is under operation 'will not 'cause the IC damage.

    TPS61086/TPS61087 's frequency at different Vin will be different, but frequency will be around the center value. for the TPS61086, when Vin=3V/Vo=12V, freq=1.01MHz, when Vin=6V/Vo=12V, freq=1.3MHz. while the center frequency for the TPS61086 is 1.2MHz. 

    The above frequency change is a common phenomenon for the constant-off time controlled Boost IC. It will not effect the normal operation.

  • 0 in reply to tateo yamashiro
    TI__Mastermind 40080 points

    To be more directly, from the block diagram, TPS61086/87 detect the average SW voltage as the Vin . So the control Vin voltage has nothing to do with the frequency. What determines the frequency is only the power VIN. 

    So the customer needn't worry about the usage. :)