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BQ25890H: proper cable selection

Part Number: BQ25890H

I'm trying to understand the proper USB cables to use with this part for the higher current modes.  If I look in the USB 2.0 spec I see USB cables are about 28AWG and if I look in the USB power Delivery introduction from USB.org I see that traditional cables are limited to 1.5A.  

Now if I go check out the reference board manual for this charger it looks like TI was happily drawing the full 3.25A using what looks to be a pretty standard USB cable.  Can you help me understand what the right thing to do here is?  I'm reading through the USB specs trying to wrap my head around it and any input is appreciated.

Thank you

  • Guru 56255 points
    Eric,

    The bq25890H does not fully interface with USB PD connectors. You will likely need an interface chip for full compability with USB PD. The bq25890H is designed to operate with USB BC 1.2 specification, which includes USB 2.0/3.0 ports as well as 5V DCP (non USB) adapters up to 3.25A output. In addition, because the host I2C can write to the charger's I2C registers that control the voltage levels of the D+/D- lines, this charger can interface with certain other High Voltage DCP (HVDCP) adapters, telling them to raise their output voltage from 5V to 9V or 12V, thereby reducing input current. You can get more detail at www.ti.com/.../slua786.

    That said, you can control the input current to the charger via an external resistor on the ILIM pin or I2C registers (called INDPM). In addition, you can set a VBUS voltage threshold below which the charger will not let VBUS fall (called VINDPM). As if that wasn't enough to prevent adapter collapse, this charge has an ICO feature which will automatically roll back the input current to prevent hitting VINDPM. More info on that feature at www.ti.com/.../slva812.

    Most customers choose a cable with resistance that will not allow the input voltage to the charger to droop below the VINDPM threshold at maximum adapter current. The VINDPM threshold should be set high enough to prevent the charger's buck converter from entering max duty cycle. You can compute this recommend value from equation 5 of www.ti.com/.../slyt569.pdf and the charger's FET resistances from the bq25890H datasheet.

     

  • In reply to Jeff F:

    When you say it doesn't fully interface with PD connectors is this because it doesn't support looking at the CC lines?  I had thought about using an MSP430 I have in the system to check the voltage there and adjust my current draw accordingly.

  • Guru 56255 points

    In reply to Eric Steimle:

    Yes.  Without the CC lines, you can't fully interface with USB PD.