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Original question:

SN74AXC8T245: Synchronously drive a 50MHz clock with a data line

BQ76952EVM: High current motor application

Danilo A.
Mastermind 24715 points
Part Number: BQ76952EVM
Other Parts Discussed in Thread: BQ76952

Hi Team,

Can you please help us with this inquiry from our customer?

What is maximum Ampere output of EVM board?

I plan to accurately measure current on various boards without limiting the output current. Because my system(motor) needs like 100 Ampere. so I planned to use the below structure.

This card will measure the current passing through the main board, and will protect the system through a fuse if the current exceeds a certain level. The switch on the board will allow for disconnecting the output of the main board. the shunt resistor is going to be on current board and it will connect directly to my main board over pins (headers).

Do you think this structure can work to measure all the current that i use ? i hope that i made my question clearly.

Regards,

Danilo

  • 0
    TI__Mastermind 27830 points

    Hello Danilo,

    Although the BQ76952 IC has no maximum rating for the current flow, the EVM board has a recommended maximum of 6-A. The board was not designed with higher DC currents in mind.

    I am a bit uneasy about the block diagram they shared. The charger should be connecting to the PACK+/- connection, not directly to the cells. Can you confirm how they were thinking of connecting it? Do they have protection FETs?

    I have no issues with anything else. But if they want to test for 100-A they would have to do so with their board. The BQ76952 can support it, they just have to design their board to account for 100-A of current flowing through it.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    TI__Mastermind 24715 points

    Hi Luis,

    Thank you for your comments. Please see the response of our customer below.

    What kind of fets and shunt resistor that i can use to make my output able to give me 120 A and measure it ?

    Regards,

    Danilo

  • 0 in reply to Danilo A.
    TI__Mastermind 27830 points

    Hello Danilo,

    A 1-mOhm sense/shunt resistor is able to measure currents of up-to 200-A (The Coulomb Counter ADC has a recommended range of -200mV to 200mV). At 120-A, you will need a 1-mOhm resistor that can handle 120-mV*120-A = 14.4-W of current. The largest shunt resistor value they could use would be ~1.67-mOhm (~1.67mOhm*120A = ~200-mV)

    You can also use smaller sense resistors too if needed, for example a 0.5-mOhm shunt resistor would be able to read up-to 400-A of current, at 120-A it would require a power rating of 60-mV*120-A = 7.2-W. However, the downside is that the device becomes worse current measurement at very low currents. The current resolution of the ADC is typically 7.6-uV divided by the shunt resistance. At 1-mOhm this is ~7.6-mA of current resolution, at 0.5-mA this resolution doubles and becomes 15.2-mA. There are also other error factors that may affect current accuracy, which are listed in Section 7.15 Coulomb Counter of the datasheet.

    We often see customers parallel multiple shunt resistors in order to handle the higher the higher currents. They will have to decide what best fits their requirements.

    Regarding the MOSFETs, this is also dependent on what current they need, how much heat they expect the FETs to generate and other factors. Typically we use N-Channel power MOSFETs. We have an application note that may aid them in deciding what kind of FETs they will need: Multiple FETs with the BQ76952, BQ76942 Battery Monitors.

    Hope this helped, let us know if there are any other questions!

    Best Regards,

    Luis Hernandez Salomon