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BQ24170

golan kormian
Intellectual 880 points
Other Parts Discussed in Thread: BQ24170, TPS22965

hi,

i intend to use the BQ24170  for application that need about 10-8W or higher, the thing is that i intend to use FET like IRLHS6242PbF at the input * 2, and CSD25401Q3 for the battery output.

if across the application i will have current of 4A through the input FET and 4-5A from battery during discharge, can i use the SMT FET or do i need larger one (like D-PACK) with heat sink.

can i relay on the thermal pad at the PCB for heat dissipation?

  • 0
    TI__Mastermind 31120 points

    A general rule is to pick and FET IC with twice the current rating that the average current for the application.  This is mainly due to how they spec the FETs....Its max current rating is typically at 25C and for higher temperature operation  the FET has to be derated.

    I typically use the rule of thumb at least 2 sq inches of directly tied copper per watt of power dissipation.  The FETs should operate in the fully on region so there should not be too much power dissipation (0.5W for 4A through 30mOhm RDSon).

  • 0 in reply to Charles Mauney
    Intellectual 880 points

    hi,

    thanks for the replay.

    so for the output of the BQ24170, if I will need during battry back up the whole 4A i used the CSD25401Q3 (same at the EVM) is it OK?

    during battery discharge is there any current discharge limitation from the battery (from the BQ24170)?

    Other question regarding FET, if need to switch lines where there will be current of average 2-3A. the pick current can be as high as 5A. i need to switch the line for backboost switcher from 3.8V (LI-PO battery 9A)  to 24V, and the switch is intend to charge large capacitor 0.1F at the input of the backboost ( for compensation).

    i intend to switch the lines with tps22965 since  the control on the IC is one logic line from MCU , simple solution.  do u think its wise selection or i need different FET for the line switching? attach the schematics

    4011.backup supply 24V PAGE1.pdf

  • 0 in reply to golan kormian
    TI__Mastermind 31120 points

    The EVM part was chosen to work for all ranges of the part and the BAT FET is rated for 14A which is over twice the 4A you need (passes rule of thumb).

    Ask the battery manufacturer questions on the battery, but in general long term load should be less than 1C, short turn <100ms <10% duty cycle, 2C; and high current <4C <0.5ms;

    I do not understand your other questions, but in general if you do not exceed the voltage rating of the electric components or 1/2 the average current you should be fine.

    I would suggest having an experienced engineer review the design.