• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Subscribers 63 subscribers
  • Views 540 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ25071: Solar Charging and Minimum Current Requirement

nack dack
Prodigy 90 points
Part Number: BQ25071
Other Parts Discussed in Thread: BQ24650,

Hello,

We are evaluating using either the BQ25071 or BQ24650 for Solar Charging a LiFePO4 battery: The questions are related to the BQ25071. We see that the BQ25071 is simpler and optimized for LiFePO4, however does not have the VDPM explicitly called out in specs unlike the BQ24650. Here's our Solar and Battery Specs:

Solar Panel: I sc=165mA; Vosc=4.8v; Vmppt=4v; Imppt=150mA

Battery:

  • A 1550 mAh LiFePO4
  • Nominal Voltage of 3.2v
  • Charging voltage of 3.65+/- 0.05v
We will have the ISET limit set to 150mA by choosing the 1.5Kohm Resistor value.
It's all well and good under good sunlight conditions with power generated at 150mA/4v, however under non optimal solar irridance conditions we will have a much lower power generated.
Assuming that we will have current let's say in the 50mA range and the voltage Vin into BQ25071 meets all the other minimum conditions (VULO < Vin  and Vin > VBAT + VSLP):
 
Would this low current be able to charge the battery? (example condition of lets say voltage of 3.9V and Current of 50mA and VBAT at 3.5v)?
If not, what are the minimum current requirements? We would like to get the charging trickle as much as we can as the device will be outdoors for most of the day.
Does the current limit setting of 150mA affect the 50mA charging?
If you have any Appnotes/pointers on the usage of BQ25071 for solar harvesting, please let us know.
Thanks,
Krishna
  • 0
    TI__Guru 73696 points
    The BQ25071 does not have VDPM or MPP function to work with a solar cell.
    The better device to use here will be BQ24650.
  • 0 in reply to Bill Johns
    Prodigy 90 points
    Thanks Bill.

    Yes, we understand the lack of VDPM/MPP function on BQ25071. However, we wanted to see if the current control function through ISET is equivalent to current control mechanism through VDPM in BQ24650. Both seem to limit the input charge current to a threshold through resistor setting which would regulate it to the needed V/I point of the MPPT. What else is BQ24650 doing to get to the optimal V/I point that BQ25071 is not doing?

    The reason for BQ25071 is the cost and simplicity. Appreciate your support and help.

    Thanks,
    Krishna
  • 0 in reply to nack dack
    Prodigy 90 points
    Upon digging further, we see that ISET mechanisms and VDPM solutions are not equivalent.

    Thanks,