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LM73605: 73605 output rising time

Part Number: LM73605

Hi Team,

My customer use LM73605(first stage)+PMIC(second stage). And PMIC have rising time requirement, which is less than 1.5ms.

How could we adjust LM73605 output rising time to meet PMIC input rising time request?

Customer try to adjust CSS with open cap, but the output rising time is 2.74ms > 1.5ms.

How to configure 73605 output rising time to make it less than 1.5ms? thanks!

  • Hello Amelie,

    If you need a soft start time (Tss) to be less than the internal ramp, please follow the guide lines in the Datasheet.  That is, to use the enable pin and also the tracking function to set Tss to the desired time.  See excerpt from the datasheet (page 18) and follow the recommendations therein.

    hope this helps?


  • Hi David,

    Thanks for your reply. 

    Here are two question about the external ramp.

    What is the voltage in SS/TRK need to set? 1.5V to 3.3V?

    How to choose the value of RTRT and RTRB to make the Tracking With Shorter Start-up Time Than the Internal Ramp?

  • Hi Amelie, 

    I believe the RTRT and RTRB SS/TRK pin need to be set such as when the EXT RAMP is finished, the voltage on the pin is greater than 1.5V.

    Based on the datasheet, in order to make the startup time shorter than internal ramp, the EN pin have to come up first while keeping the SS pin 0V.  After internal ramp (dotted line) is finished ~7ms after EN is up then the EXT RAMP signal can be applied. 

    You may try this method and see if that helps.