对于bq25570,我测试自己的电路发现,无论Voc_SAMP接地还是接VSTOR,最后给电池充电的速率都不变。后来我看手册,猜测是CREF上的电压没有保持住,导致MPPT没有正常工作(期间还尝试用ROC1,ROC2的不同搭配,但是基本没什么变化。甚至我直接把CREF拆下来之后,充电速率都和之前差不多,因此我怀疑是MPPT没正常工作)。请为我分析原因,谢谢
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.
对于bq25570,我测试自己的电路发现,无论Voc_SAMP接地还是接VSTOR,最后给电池充电的速率都不变。后来我看手册,猜测是CREF上的电压没有保持住,导致MPPT没有正常工作(期间还尝试用ROC1,ROC2的不同搭配,但是基本没什么变化。甚至我直接把CREF拆下来之后,充电速率都和之前差不多,因此我怀疑是MPPT没正常工作)。请为我分析原因,谢谢
Hi
CREF needs to be very low leakage = high insulation resistance = high voltage rating. Please see the EVM BOM for an example.
The charger is a boost only charger, meaning VIN_DC < VBAT_OV setting. Grounding VSTOR with an input applied at VINDC prevents MPPT and switching from functioning because the chip is powered by VSTOR after VSTOR>1.9V. There is a diode path from VIN_DC to VSTOR.
Also, if you are using resistors in the 10Megohm range, keep in mind that the following from the datasheet:
In order to maximize efficiency at light load, the use of voltage level setting resistors > 1 MΩ is recommended. In addition, the sample and hold circuit output capacitor on VREF_SAMP must hold the voltage for 16s. During board assembly, contaminants such as solder flux and even some board cleaning agents can leave residue that may form parasitic resistors across the physical resistors/capacitors and/or from one end of a resistor/capacitor to ground, especially in humid, fast airflow environments. This can result in the voltage regulation and threshold levels changing significantly from those expected per the installed components. Therefore, it is highly recommended that no ground planes be poured near the voltage setting resistors or the sample and hold capacitor. In addition, the boards must be carefully cleaned, possibly rotated at least once during cleaning, and then rinsed with de-ionized water until the ionic contamination of that water is well above 50 MOhm. If this is not feasible, then it is recommended that the sum of the voltage setting resistors be reduced to at least 5X below the measured ionic contamination.
Regards,
Links
Can you provide some oscope plots of VIN_DC, VSTOR and LBOOST? If your input source has HiZ source, like a solar panel, then VIN_DC should be regulated to MPPT%*VIN_DC. You can't measure the VREF_SAMP cap voltage using a 10Meg scope probe because it loads it too much but you could use DMM voltmeter set to 1Gohm output impedance to measure its avg dc voltage.