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TPS7A53: the difference between Tss and Tref

Part Number: TPS7A53

Hi team

We can see the definition of Tss in the datasheet and can see the definition of Tref in the app note as below to calculate the start up time. Is it OK that Tss and Tref are identical?


Noriyuki Takahashi

  • Hi Takahashi-san,

    So yes, both the Tss in the datasheet and the Tref in the app note are representing the rise time of Vref to steady state value. Tss is defined as the voltage on the soft start capacitor, which follows Vref as it rises, and Tref is defined as the voltage on Vref itself. Because these voltages follow each other, both designate the same time period so their calculation should be an identical quantity.

    The naming of Tref in the app document is most likely due to being for all LDO configurations. Some products have SS/NR pins and some do not, naming that time Tss could cause confusion as all startup circuitry is non-programmable by end users in LDO's without a SS/NR pin. Therefore labeling it at Tref more clearly describes it as the time it takes for Vref to ramp to it's operating value, Tss would represent the time for the voltage rise on the internal Vref startup capacitor, which while it is the same value, it requires a bit more understanding of the internals of the LDO in order to know that. Hope this helps