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TPS543C20AEVM-054: compensate function

Yiwen Huang
Prodigy 20 points
Part Number: TPS543C20AEVM-054
Other Parts Discussed in Thread: TPS543C20, TPS543C20A

Hi,

May I know R3, C18, C19 placeholder is type3 compensate in the TPS543C20 EVM schematic?  and I want to fine turn transient performance, which placeholder can adjust?

Thanks.

  • 0
    TI__Genius 17905 points

    HI Yiwen,

    For fine tuning transient performance, you can modify R2 (ramp setting) resistor among the options mentioned in Table 3 of the datasheet.. Higher R2 will select a higher internal ramp capacitor which will typically increase the loop bandwidth which will help transient response. Increasing the bandwidth can come with a tradeoff of lower phase margin, so it is important to evaluate stability when doing this (by measuring bode plot and/or checking for ringing in transient response). 

    If your output voltage is higher than the Vref options such that you need a feedback resistor divider, then you can also try adding a feedforward capacitor C22 (in parallel with your R12 top feedback resistor) to increase bandwidth and improve transient response. Check the bode plot and load transient for acceptable performance.

    Regards,
    Kris

  • 0
    TI__Guru 56815 points

     

    Components C18, C19 and R3 are not used by the TPS543C20A and

    They were included in the PCB layout / and schematic to compare the performance of the TPS543C20A's Advanced Current Mode Control with a Voltage Mode Control Loop, which used Type-3 Compensation.  That design used Pin 40 as the output of the voltage mode error amplifier.  The Voltage Mode device was a test-chip and is not available.  Populating C18, C19 or R3 could affect the resistance detection of R2 and is not recommended.

    C22 and R9 is a high-frequency output voltage feed forward circuit which cancels the effects of the R5/R12 feedback divider at high frequencies to improve transient response while maintaining accurate DC regulation. In designs that use a feedback divider to increase the output voltage, the addition of a feedforward capacitor (C22) can boost the phase margin near crossover and increase the loop gain.

    As  mentions, adjustment of the transient response should be done by selecting a Ramp capacitance (Cramp) through the selection of R2, and, if VOUT is not equal to the reference voltage, the feedforward capacitor C22.