BQ24650: BQ24650RVAT: Maximum Charge Current

Nicholas Ipri1

Prodigy 200 points

Part Number: BQ24650
Other Parts Discussed in Thread: CSD18502Q5B,

Am thinking about using this part to charge lead acid batteries with a maximum charge current of 10A.

Using TI CSD18502Q5B MOSFETS and Coilcraft SER2915 series inductor.

Will this work?

Thanks!

over 4 years ago

0 Jeff F over 4 years ago

TI__Guru*** 143910 points

Nicholas,

The BQ24650 HI and LO gate drivers should be able to drive the FETs hard enough to get 10A. With the correctly sized inductor for the VBUS to VBAT delta and desired current, and related, voltage ripple, that inductor should work. I recommend reading the two appnotes below if the application is for solar charging:

Regards,

Jeff

0 Nicholas Ipri1 over 4 years ago in reply to Jeff F

Prodigy 200 points

Thanks!

0 Nicholas Ipri1 over 4 years ago in reply to Nicholas Ipri1

Prodigy 200 points

Asking a related question: I want to implement the charging circuit in figure 2 of appnote SLVA437SA "Using the bq24650 to Charge a Sealed, Lead-Acid Battery"

1) If I were to power my system load directly from the battery pack e.g. the node of D3, R6, R23, etc, would this confuse the charging process by drawing too much load current through R6 (Rsr)?

2) If I power my system load from the recommended node, it looks as though the load powers from Vin when Vin > Vbattery pack and from Vbatterypack otherwise. How can I assure that the load power is uninterrupted when near the transition?

0 Jeff F over 4 years ago in reply to Nicholas Ipri1

TI__Guru*** 143910 points

Hi Nicolas.

Regarding 1, the charger limits the output current to the programmed value per RSR. If your load load connected in parallel with the battery draws all of that current, then the battery will not charge. Also, with an almost charged battery, the charger will not be able to distinguish between load and termination current so the charger will likely never report charger termination correctly.

Regarding 2, if the VIN and battery nodes are properly diode ORd, the transition is seamless.

Regards,

Jeff

0 Nicholas Ipri1 over 4 years ago in reply to Jeff F

Prodigy 200 points

Got it, thanks!

0 Nicholas Ipri1 over 4 years ago in reply to Nicholas Ipri1

Prodigy 200 points

Another related question! If I were to use my host processor to monitor battery voltage and charge current while controlling the MPPSET pin. I could implement the pulse charging algorithm as described in the appnote for charging lead acid batteries without the added components. My ideal goal is to power my load directly from the battery while charging while eliminating the ORing diodes in the process.is this feasible?

0 Jeff F over 4 years ago in reply to Nicholas Ipri1

TI__Guru*** 143910 points

Nicolas,

Yes!

Regards,

Jeff

0 Nicholas Ipri1 over 4 years ago in reply to Jeff F

Prodigy 200 points

Thanks again, that's a huge plus that will help this part fit perfectly in my design

0 Nicholas Ipri1 over 4 years ago in reply to Nicholas Ipri1

Prodigy 200 points

One more... The example ckt on p23 has D2 as a BAT54C which is a dual diode. Am assuming that the 2nd diode is unused and just want to confirm.

0 Jeff F over 4 years ago in reply to Nicholas Ipri1

TI__Guru*** 143910 points

Hi Nicholas,

I think the part number is a typo. It should be the single diode version of the BAT54.

Regards,

Jeff

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BQ24650: BQ24650RVAT: Maximum Charge Current