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BQ25798: BQ25798

Pushpendra Singh
Prodigy 70 points
Part Number: BQ25798

Tool/software:

Hello!

My team and I are currently working on integrating the BQ2598 Charger Chip into our hardware design. We are using the BQ25798EVM board for reference to verify our readings and to identify any discrepancies in our design. One observation we have made is during the application of a 5V simulated solar panel voltage to the VAC2 input (second input source), we aimed to evaluate how the charger's efficiency varies with different IBUS values. We simulated the current and limited it from 100mA to 600mA in intervals of 100mA, with the following results:

Calculations  
 VAC2 IBUS Input Power VBAT IBAT Output Power Difference in Power Difference in Current
4.934V 0.125 0.61675W 3.257V 0.015 0.048855W 0.567895W 0.11
4.924V 0.225 1.1079W 3.291V 0.104 0.342264W 0.765636W 0.121
4.948V 0.33 1.63284W 3.316V 0.254 0.842264W 0.790576W 0.076
4.950V 0.423 2.09385W 3.339V 0.384 1.282176W 0.811674W 0.039
4.966V 0.511 2.537626W 3.35V 0.481 1.61135W 0.926276W 0.03
4.989V 0.619 3.088191W 3.397V 0.622 2.112934W 0.968897W -0.003
               

To further investigate, I tested the same scenario on the EVM board with the help of Battery Management Studio and its ADC readings, and while there were some minor differences in IBAT (within a few mA), the results were largely consistent.

My main inquiry is whether there is a way to improve efficiency on the VAC2 input, which is configured for a 5V, 600mA max solar panel, but only delivers around 2.5W in the field. We observe significant power loss between input and output without noticeable heating in the charger, which raises the question: Where is this power being dissipated? Could it be grounding losses, and should this be a concern? Additionally, are there steps we can take to enhance efficiency on VAC2, particularly with solar panel usage?

We are not concerned with the efficiency of the VAC1 input (12V), but we seek insights specifically for VAC2 as it will be driven by a solar panel. Any guidance on improving efficiency or understanding the power loss would be greatly appreciated, especially since the EVM board readings match our hardware results.

Thank you for your time and assistance.

Regards,

Pushpendra Singh