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TPS549B22: can I directly replace the TPS548B22 as a 2nd source

user5968756
Prodigy 190 points
Part Number: TPS549B22
Other Parts Discussed in Thread: TPS548B22

Hi Expert,

I use the TPS548B22 and we face a shortage of that part, Can i directly use the TPS549b22 as a 2nd source? Thanks.

I check the datasheet, i found 2 difference. 

1. pin1,2,3 will be left open, i think it is OK?

2. pin32, FSEL, i attach the existing schematic, will it works for TPS549B22 with its default image. 

Regard,

Alex

  • +1
    TI__Mastermind 48140 points

     

    user5968756 said:
    I use the TPS548B22 and we face a shortage of that part, Can i directly use the TPS549b22 as a 2nd source? Thanks.

    The TPS548B22 and TPS549B22 are generally compatible, but have some minor differences. whether they can be used as a direct drop-in replacement depends on the circuit they are used it.  In particular, the programming of switching frequency and internal compensation ramp programmed off of the FSEL pin, which becomes the ADDR pin on the TPS549B22 and the  (See Below) and Pins 1, 2, and 3 become SMB_ALERT#, PMB_DATA, and PMB_CLK respectively.

    user5968756 said:
    1. pin1,2,3 will be left open, i think it is OK?

    Since the application will not be using the PMBus, it is ok for the pins to be left open.

    user5968756 said:
    2. pin32, FSEL, i attach the existing schematic, will it works for TPS549B22 with its default image. 

    The TPS549B22's default  Switching frequency and Ramp selection is 650kHz with the R x 1 ramp, and this is not programmed by the ADDR pin, so the loop performance of the circuit with the TPS549B22 will decrease due to the larger injected D-CAP3 ramp.  That change will decrease the loop bandwidth and increase the output voltage overshoot and undershoot during a dynamic load change.

    If that increased output voltage overshoot / undershoot is acceptable, you will be able to replace the TPS548B22 in your design with the TPS549B22. 

    To change the default ramp generator time-constant to use the R x 3, the TPS549B22 would need to be programmed via PMBus to change the D3h command value and store that value to NVM memory.

    See https://www.ti.com/lit/ds/symlink/tps549b22.pdf#page=38 for details.