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Part Number: BOOSTXL-BATPAKMKII
I'd like to understand why, on the BATPAKMKII, the voltage input for the two regulators (U3 3V3, U4 5V) is directly connected to the battery pack, i.e. BAT pins on the BQ24250 charger.
I'd expect the voltage input of those regulators to be connected to the SYS pins of the charger, enabling the system to be supplied by the USB VBUS whenever VBUS available, effectively having the battery pack as a backup power supply.
What's the reasoning for this? Is my understanding of the SYS pins of the battery charger correct?
Thanks in advance.
in case you didn't do so yet I'd encourage you to have a look at the Fuel Tank KMII Battery BoosterPack Plug-In Module User's Guide as it describes the Hardware of the BoosterPack you're working with. The User's Guide both describes the signals and the functionality of the different power devices on the PCB.
Please come back to us in case there are still pending questions after looking at the document.
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In reply to Britta Ruelander:
Thank you for the reply.
I found this on the User Guide:
"The input to the TPS63001 is the PAK+_OUT signal directly from the battery. Because of the direct battery connection, configuration of the fuel gauge and Li-Ion charger are irrelevant to this voltage output."
So I understand the decision to connect voltage input of the regulator to the battery, instead of connecting it to the SYS out from the charger, is just so if you mess up with the charger in any way, the voltage output will not be affected.
However, the more typical application would be to connect TPS63001 voltage input to the SYS output of the battery charger, correct?
In reply to Pedro Mietto83:
For more information on buck-boost devices have a look at www.ti.com/buckboost
In reply to Brigitte:
I will add this from page 7 of this document.Fuel Tank MKII Battery BoosterPack™ Plug-in Module (BOOSTXL‑BATPAKMKII) www.ti.com/.../slau618a.pdf The bq24250 Li-Ion battery charger provides its own regulated DC-DC output on the SYS pin. In many applications this output is used to provide system power. On the Fuel Tank MKII BoosterPack plug-in module, this output is placed onto a test point for access (TP4), but not explicitly used to power the connected LaunchPad development kit. This demonstrates the flexibility of the design.
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