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TPS7A91: Transient preference

Hailiang Zhang
Genius 11080 points
Part Number: TPS7A91
Other Parts Discussed in Thread: TPS7A92

Tool/software:

Hi Expert,

The customer reported that the TPS7A91 output voltage dropped 30mV when there was a transient current (rising from 40mA to 712mA in 4us). The customer wanted to know

  • If the transient performance of the TPS7A92 is expected to be better? Can the voltage drop be reduced by switching to the TPS7A92?
  • What is the maximum output capacitance allowed for the TPS7A91?

Regards,
Hailiang

  • 0
    TI__Genius 13680 points

    Hi Hailiang,

    30 mV drop is within the expected limits for this device. The load-step transient response is the output voltage response by the LDO to a step change in load current. The depth of charge depletion immediately after the load step is directly proportional to the amount of output capacitance. However, although larger output capacitances decrease any voltage dip or peak occurring during a load step, the control-loop bandwidth is also decreased, thereby slowing the response time.

    I would start with increasing output capacitance and reducing the current slew rate if possible.

    Hailiang Zhang said:
    If the transient performance of the TPS7A92 is expected to be better? Can the voltage drop be reduced by switching to the TPS7A92?

    Yes, TPS7A92 will have slightly better transient response for similar conditions. I would not rely on switching to TPS7A92 for significant improvement in the load transient. 

    Hailiang Zhang said:
    What is the maximum output capacitance allowed for the TPS7A91?

    There is no stated maximum. However, the benefits of adding more output capacitance diminish beyond a certain point which can be determined only in lab

    Regards

    Ishaan