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TPS544B20: overshoot issue during TPS544B20 start up

Oliver Ou
Intellectual 2845 points
Part Number: TPS544B20

Hi,

Customer found TPS544B20 would have a overshoot during start up condition with default setting.

Here is the schematic. could you give some suggestion how to avoid the issue?

Thanks.

  • 0
    TI__Guru 56815 points

     

    The TPS544B20 datasheet describes the small overshoot of the output voltage at the end of soft-start in section 8.3.7 Soft-Start on page 20.

    http://www.ti.com/lit/ds/symlink/tps544b20.pdf#page=20

    During Soft-start, the internal error amplifier forced the COMP voltage to track the internal reference so that the current charging the COMP to AGND capacitor does not introduce an offset voltage.  Because D-CAP2 regulates to the valley if the injected ramp + the feedback voltage, the feedback voltage exceeds the reference by 1/2 of the injected ramp amplitude.  Once the converter completes soft-start, the error amplifier changes to transconductance mode and the overshoot is removed by the integrator.

    Decreasing the soft-start time (TON_RISE) can reduce the overshoot slightly.

    Decreasing the R176 resistor (COMP to AGND) will not decrease the overshoot, but will help smooth the transition from the overshoot into normal regulation.