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BQ24170: Application schematic details

Gerhard Braun
Prodigy 40 points
Part Number: BQ24170

Hi,

my application is a 2-cell charger  with 12V input and 3A charge current. System connected to battery. 

I refer to Fig. 23 of the datasheet:

Which input capacitor is required? The schematic says 4,7µF. The datasheet recommends 20µF (page 26).

There is a diode connected to SW-Pin. What type of diode is required? Is this diode mandatory? Why does the Evaluation Module not contain this diode?

There is another optional diode between BTST and REGN. When is this diode required? What type of diode is required?

In Fig. 19 there are another 2 diodes connecting VBAT or Adapter to AVCC. When are these diodes required? What type of diodes?

Thank you for your help!

Regards

Gerhard

  • 0
    TI__Expert 8690 points
    Hi Gerhard,

    You can follow our EVM guidelines and schematics here: www.ti.com/.../sluu463.pdf

    The EVM does contain the diode (D2).

    As for the diodes connecting VBAT or Adapter to AVCC, these diodes are needed when you have AVCC connected before the ACFET (Q2 and Q3 on the EVM schematic). When in battery only, Q2 and Q3 are open, not allowing AVCC to be powered by battery through the high side FET. Internal logic uses AVCC.

    Regards,
    Steven
  • 0 in reply to Steven Bangdiwala
    Prodigy 40 points
    Hi Steven,

    sorry I don't understand your explanation regarding the diodes:
    You wrote: As for the diodes connecting VBAT or Adapter to AVCC, these diodes are needed when you have AVCC connected before the ACFET (Q2 and Q3 on the EVM schematic). When in battery only, Q2 and Q3 are open, not allowing AVCC to be powered by battery through the high side FET. Internal logic uses AVCC.

    Do you mean that the diodes supply the AVCC Pin? I think this is done internal in the IC: The datasheet says: a conduction path exists from the battery to AVCC through the high-side NMOS body diode. I think this is the body diode of the internal FET between PVCC and SW. Is this correct?)

    I think that the diodes prevent a reverse current from AVCC into the adapter. Is this correct?
  • 0 in reply to Gerhard Braun
    TI__Expert 8690 points
    Gerhard,

    Yes, the conduction path from battery to AVCC can be through the high side NMOS body diode, but if you use the ACFET (Q2 and Q3 on the EVM), then the path is blocked. You will need to use a diode from battery to AVCC to make sure logic still works for battery only operation.

    Regards,
    Steven