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BQ25895: Interfacing with TS5USB410

Alfred Logico
Expert 5060 points
Part Number: BQ25895

Hi Team, 

I have questions from my customer on how to interface our BQ25895 with our TS5USB410. Below are the questions:

I’d like to clarify some points and feature of the BQ25895 charger and TS5USB410 USB MUX. What we want is an automatic USB detection without the help of CPU and SW/FW. If an empty battery is attached, the circuit should automatically charge the battery once device is connected to a USB port or other power source.

  1.  On BQ25895, SW voltage is maintained at 3.5V whenever there is a source connected to VBUS pin (assuming VBUS voltage > 3.6V). Is this assumption correct?
  2. On BQ25895, which happens first: DSEL pin going LOW or start  of Input Detection? We plan to use DSEL pin of BQ25895 to control and set the SEL1/SEL2 pins of TS5USB410. DSEL pin is an open drain output and we plan to use a buffer which can set SEL1 & SEL2 pins of TS5USB410. Please advise on the possible conflict when BQ25895 starts input detection but the MUX switching is delayed. Does BQ25895 detect input only once?
  3. Will there be a conflict connecting DSEL pin to SEL1 & SEL2 pins? We believe a buffer is still needed. Do you have a better solution for the MUX to have a more automatic switching?

What we have in mind so far is to use a buffer to drive the SEL pins of TS5USBC410I as shown below:

 

REGN_4V8 is the output of the internal regulator of BQ25895. Our concern is the sequence in which DSEL is asserted and de-asserted. The sequence we have in mind is that:

 

  1. TS5USBC410I USB MUX switches the input USB lines to either the CPU or going to BQ25895 charger.
  2. By default, the USB MUX connects the USB input lines to USB Port of CPU, not going to charger. (DSEL=HIGH,SEL1=HIGH, SEL2=HIGH)
  3.  When our device connects to a USB port, BQ25895 goes through its initialization up to Input Detection Sequence.
  4. DSEL is supposed to go LOW during Input Detection so USB MUX switches the USB lines to connect to the charger. (DSEL=LOW,SEL1=LOW,SEL2=LOW)
  5. Once detection is finished, DSEL line goes HIGH and USB MUX switches back to the default which connecting to CPU.

 

Please advise if this is such the characteristic of BQ25895 detection.

Thanks! 

Best Regards, 

Alfred

  • 0
    TI__Genius 10240 points
    Alfred,

    It is correct that VBUS needs to be 3.6V minimum for the with the assumption that the battery is depleted. The VBUS has to be higher than the VBAT + V(sleep) for the converter to switch. For the USB detection, a simple solution is for the application processor to set high impedance state of D+/D- and wait for the first one second when VBUS power is applied. BQ25895 drives the D+D- and finishes the detection (no HVDCP) in less than one second.