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BQ25790: About OTG mode

Part Number: BQ25790

Hi,

Could you tell me about BQ25790 OTG operation.

1.Is it possible to change the BOOST voltage dynamically during OTG operation?

2. Is there a maximum output power regulation for OTG?
 For example, is it possible to boost the 1-cell voltage (2.8V~4.4V) to 22V / 3.32A?
    Does BQ25790 have protection features such as OTG Ilimit?

Best regards
Yusuke

  • Hi Yusuke-san,

    Regarding 1, yes.

    Regarding 2, if you disable battery discharge regulation, then the cycle-by-cycle current limit of Q1 (7.5A min) or Q2 (10A min) will limit the output the power, causing VBUS to droop.  If your customer wants a hard stop, they can use IBAT_OCP (9.3A min).  Battery over-current protection is available when external ship FET (SFET) is assembled, SFET_PRESENT bit is set to 1, and EN_BATOC bit is set to 1. When discharge current exceeds IBAT_OCP, the SFET turns off to stop the discharge current. 

    Regards,

    Jeff

  • Hi Jeff-san,

    Thank you for your kind support.
    Is the current limit of OTG listed in the electrical characteristics?
    Does it mean the same as the IBUS OCP spec?



    I want to know the exact specifications to maximize the OTG output current.

    Best regards
    Yusuke

  • Hi Yusuke-san,

    IBUS_OCP is only for forward charge mode.  For max OTG current, I recommend disabling IBAT_DCHRG (REG0x0Db6:) and disabling IOTG_LIMIT (REG0x14b2).  Max OTG current will then be limited by max input current as limited by cycle-by-cycle current limit.

    Regards,

    Jeff

  • Hi Jeff-san,

    Thank you for your explanation.
    I understand the settings for REG0D and REG14 .

    > if you disable battery discharge regulation, then the cycle-by-cycle current limit of Q1 (7.5A min) or Q2 (10A min) will limit the output the >power, causing VBUS to droop.  If your customer wants a hard stop, they can use IBAT_OCP (9.3A min).

    Are the limit values for Q1(7.5A) and Q2(10A) listed in the data sheet?
    What is the basis for our calculation of maximum OTG current?
    For example, Could you tell me the case where the battery voltage is 2.8V and the OTG output is 20V?

    Best regards
    Yusuke

  • HI Yusuke-san,

    The cycle-by-cycle limit values are not in the datasheet.  The easiest way to estimate the power requirements for a CCM boost converter is using efficiency power balance, eff=Pout/Pin=20V*IOTG/(2.8V*IBAT).  Unfortunately, I don't have data for efficiency that low but it will quick low, probably below 80%.  

    Regards,

    Jeff