TI中文支持网Part Number:BQ25570
I originally planned to connect a 3.7V 280mAh lithium battery to VBAT, while a load (operating voltage 3.7V, average current <100mA, peak can reach about 800mA) is connected in parallel to the lithium battery, with a load switch in between controlled by VBAT_OK to turn ON/OFF. When not charged to VBAT_OK_HYST, the switch is in the OFF state. I see that the BQ255 series recommends connecting the load to VSTOR, but I noticed that the Iout of BQ25570 is only 100mA peak, does this mean that the FET between VBAT and Vout only supports a current of 100mA? I assume that the FETs between VSTOR and VBAT are of the same series, so if I connect my load to VSTOR and also add a load switch in between, when charging to VSTOR_CHGEN and the FET is turned on, will the FET get damaged when the lithium battery powers VSTOR through the FET?
Vivian Gao：
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Vivian Gao：
To clarify, the 110mA Iout limit is specific to current being pulled from the Buck converter. I don't believe there is an overcurrent limit for the BAT-VSTOR FET so you should be able to pull additional current through there. One concern to keep an eye on is the thermal dissipation of the device. Given the max FET RDSON of 1.5Ohms, a 800mA load will cause about 1.8Watts of power dissipated which can cause a significant thermal increase over extended periods. The upper limit for junction temperature on this device is 125C (105C recommended max).
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ZUM ZHANG：
As you mentioned, I later realized that the biggest issues are the voltage drop and heat generation. The 1.5Ω internal resistance is indeed a significant problem, so I decided to connect the load to the VBAT battery terminal. Additionally, I have another question to ask you: When the VIN_DC of the BQ25570 cannot obtain energy from the solar panel at night, does the system enter a state where it cannot operate? If at this time my battery voltage is consumed by the load, causing VBAT = VSTOR < VBAT_OK, then does the vbat_ok GPIO fail to function normally and cannot go from 1 to 0? Is it necessary for VIN_DC to have input for the battery management logic to be valid? Our backend load continues to operate at night, causing the battery voltage to drop to a range where it cannot function normally (<2.5V), leading to an inability to go to sleep or wake up, so we need to confirm the operating state of the BQ25570 when there is no input on VIN_DC.
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Vivian Gao：
As shown in Section 7.3.2, "For the VBAT_UV feature to function properly, the system load should be connected to the VSTOR pin while the storage element should be connected to the VBAT pin. " If the load is directly connected to the battery, the device will not protect from an undervoltage scenario because the device is being bypassed. VBAT_OK samples the VSTOR voltage level, and indirectly the VBAT voltage.
If the battery is below VSTOR_CHGEN upon startup, the device will enter cold start until the VSTOR>VSTOR_CHGEN.
