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TPS715: Could you please tell me how to remove 0.6V overshoot of TPS71530 which happend at powered up?

Part Number: TPS715

 Hello guys,

 One of my customers is evaluating TPS71530 on their own board for their new products.

 In the evaluation, they found that about 0.6V overshoot was happend at powered up.

 Their TPS71530 input is connected to 5V linear regulator output.

 When the 5V regulator is powered up after long period of power off, the regulator output voltage starts rising from 0V and TPS71530 overshoot is not happened.

 But, when the 5V regulator is powered up after short period of power off, the regulator output voltage starts rising from about 1.6V

because 5V output voltage is not discharged completely.

And the 0.6V overshoot of TPS71530 is happened then.

Also the TPS71530 input voltage rising time from 1.6V to 4V (passing point) is about 80us in that case.

 The customer wants to know why the overshoot is happend and how to remove the overshoot.

 Could you please give me your reply or comment?

 Your reply would be much appreciated.

 Best regards,


  • Hi Kazuya,

    What seems to be occurring in this application is that when the 5V supply is turned off for a short period of time, TPS715 is likely being put into dropout because Vin is not going to 0V. When an LDO is in dropout the gate of the pass devices is driven by the error amp as hard as possible which makes the pass device as low a resistance as possible. Then when the input voltage rises back up, since the pass device is at it's minimum resistance the output voltage will follow the input voltage until the output voltage exceeds the intended output voltage by the accuracy (for TPS715 that is 4%) at which point the error amplifier must sense this error (which takes time due to the bandwidth/response time of the LDO) and then switch the gate of the pass device from fully on to fully off which also takes some finite amount of time. This is what causes the overshoot to occur. To eliminate this the input voltage should be further reduced to turn off the LDO so it starts up cleanly and isn't recovering from a dropout condition (this may requiring more off time or adding a small, always on load to discharge the rail). If this isn't an option, increasing the output capacitor could help reduce the overshoot.