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TPS43060: TPS43060 issue

Sunny Qin
Expert 4890 points
Part Number: TPS43060

Hi team,

My customer use TPS43060 to design a special circuit: -24V to -15V convertor, current is 2.5A, but testing result shows one issue:

When input voltage higher than -21V, like -20V or -19V or even higher, then output current can only meet 1A, or output is not stable, and MOS driver signal will missing sometimes, if input voltage is -24V or lower than -24V, then everything works good.

SCH is below:

After checked with customer we found the root course, it is because of resistor between HDRV/LDVR and MOS:

When customer use 5.1ohm resistor, issue SW wave happens as below, and if input is -18V, it can only support 0.5A load at -15V output:

But if change the resistor to 10 ohm, everything become better, when input is -18V, it can only support 2.5A load at -15V output, and SW wave is quite good:

Now customer need to know why this resistor must be 10ohm rather than 5.1ohm, and if they change the resistor to 1ohm or 0ohm, issue become even worse. But our reference design shows the resistor is 0ohm, could you help to share some comments?

Thanks very much.

Regards, Sunny

  • 0
    TI__Expert 7450 points

    Hi Sunny,

    Before I get into the details, could you confirm the switching frequency with me?

    Based on the RT=249kOhm, the switching frequency should be ~230kHz.

    The two switching waveforms you showed here seem to have different switching frequency, the upper one is about 120kHz and the lower one is about 230kHz?

    The horizontal scale is not very clear in the pictures.

    Thanks,

    Yinsong

  • 0 in reply to Yinsong Cai1
    TI__Expert 4890 points

    Hi Yinsong,

    Mang thanks for your comments, the SW frequency should be ~230kHz indeed.

    we are wondering why resistor on MOS driver need to be larger than 5ohm, in my opinion, smaller resistor will be better for MOS driving.

    Thanks.

    Regards, Sunny