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TPS628502-Q1: TPS628502-Q1

Karim CHAKHCH
Prodigy 20 points
Part Number: TPS628502-Q1

Tool/software:

Dear TI support, 

We are using TPS628502QDRLRQ1 as Buck from 3V3-1V2 with current output load  up to 2A

Here below the detailed schematic 

We observe 3 unexpected behaviors according to the configuration mode chosen 

1- SSC seems to be enabled 

2- frequency higher (2.7MHz vs 2.25MHz / 1.8MHz) 

3- High overshoot and undershoot voltage

Could you please check the schematic and setting value and provide us with the good configuration and corrective values for the following objectives : 

- Eliminate Undershoot and overshoot in the switching frequency (inductor)?

- Understand the value frequency ? why it is different from the expected configuration 2.25MHz /1.8MHz

- Disable the SSC

Thank you for you quick feedback 

Best regards, 

Karim 

  • 0
    TI__Mastermind 20820 points

    Hello Karim,

    If you are using 68k resistor with TPS628502Q then the SSC should be disabled automatically and frequency will be around 2.67MHz.. Please refer to this section of datasheet. Freq depends upon what value of resistor you connect to COMP/FSET pin. If you are looking for 2.25MHz choose the resistor accordingly. It will be around 80kohm. This is described in detail page 12,page 13 of datasheet. (https://www.ti.com/lit/ds/symlink/tps628502-q1.pdf)

    Coming to your second point, 

    This can be measurement issue? What kind of probe you are using? It is recommended to use low inductance probe something like below: Also you can refer to this app note (https://www.ti.com/lit/an/slva494a/slva494a.pdf)

    Thanks,

    Farheen

  • 0 in reply to Farheen
    Prodigy 20 points

    Hello, Thank you  for your feedback 

    We follow your test method but we didn't see any improvements on the results 

    please find here the probe used for this test :Oscilloscope Probe: Tektronix TPP0200 Voltage Probe

    Could you please check again and see if any other improvements is possible ? example : probe change, simulation ?

    Thanks 

  • 0 in reply to Karim CHAKHCH
    TI__Mastermind 20820 points

    Hello Karim,

    you have to turn off the high bandwidth also. What is the bandwidth of measuring channel?

    Please check the timing of this peak: if this is less than 10ns then in terms of abs max it should be fine.

    Thanks,

    Farheen