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Hello,
I am trying to figure out if there is a way to test this evaluation module with a 10-cell lithium ion pack without having to use JP2 and a different feedback resistor but I can not figure out if it is at all possible. I also can not find any guide on how to configure the IC for 10-cell lithium ion battery pack in general, apart from the reference electrical design.
I need to be able to demonstrate I can deliver 8A to our pack through this design and complete a charge cycle before we can go into designing a complete solution around this IC. Could you please help me with how to approach this?
Hi, by deault, we fix the battery voltage to be a certain value. Hence we have a fixed resistor value and JP1 configured. If you would like to modify it, you can eithet use JP2 or change the resistor on the EVM. That is standard procedure done by all customers and even us internally. Please see our design calculator which will enable you to design exactly as per your specifications. https://www.ti.com/tool/download/BQ25756-DESIGN-CALC/
Please also see our schemaic and layout checklist. https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1277772/faq-bq25756-schematic-and-layout-checklist
Furthermore, please see our EVM user guide https://www.ti.com/lit/ug/sluuct7b/sluuct7b.pdf?ts=1710269414574&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FBQ25756EVM
Lastly, some reference designs that might be helpful to you. https://www.ti.com/tool/PMP41062
https://www.ti.com/tool/TIDA-010240
Hopefully it helps.
This is not that helpful of an answer as I'm already aware I have to do all that work just to evaluate if it's worth using this product. You should be able to give simple guidelines for setting the EVM up for some popular battery configurations. I'm surprised that you suggest me to operate on the board instead of having a way to either do this through software or have some additional jumpers for a few cell config options.
To be honest the support for this IC is pretty bad compared to your battery protection ICs.
Furthermore, the design calculator you have doesn't have clear enough documentation. I want to set things up for a 10 cell LithiumIon battery pack. The nominal voltage is 36V but the voltage can go between 25V and 42V for regular charge and down to 20V for trickle charge. Can you tell me how I'm supposed to input this into this spreadsheet.
Also your EVM guide states this board can be used for up to 13 Lithium Ion cells in series but doesn't bother to explain how you could test anything other than the default 7S, apart from a non-clear note about JP2. Even what you wrote above is wrong. Just placing a jumper on JP2 is not enough. One has to install their own feedback resistor (onto the test points? where???) that captures somehow the correct voltage but your schematics reports 29.4V. Considering 4.2*7=29.4, I'm going to guess for 10 cells we need to choose the resistor to set this at 42, which is the maximum voltage for the 10 cell configuration.
The way to calculate the resistor divider values for 10s battery is using our design calculator or a simple voltage divider formula. A 10s battery has a battery voltage of 4.2*10 = 42V aka input. Recommended target feedback voltage aka output is 1.536V. GND is 0V. Using this, we can very easily calculate the resistor values of a simple voltage divider network. This can also be done using the design calculator in Step 6. You can customize both top and bottom resistor values if you please. You will need a 9.53KOhm bottom resistor.
The nominal voltage goes into the “Input Voltage – Nom, Vac(nom)” cell. However, the min and max input voltage are what defines the FETs and inductors that he needs for the most part.
To physically change resistors, there are 2 ways, first, you can remove JP1 and install a new resistor to JP2. You can do this by soldering a resistor to JP2 or solder a resistor onto female header and use that. Second, you can remove R64 and install the new resistor onto that spot.
Depending on your input voltage, you’ll want to change the ILIM_HIZ resistor or set EN_ILIM_HIZ_PIN=0 as well.