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LMZ34002: Slow Start if STSEL is floating

Part Number: LMZ34002
Other Parts Discussed in Thread: TPS84259

Good morning,

I'm currently trying to find out how to adjust the output ramp with the SS feature on the said part. From what I've read regarding STSEL pin : 

"Slow-start select. Connect this pin to A_VOUT to enable the internal SS capacitor." 

1- From my understanding, correct me if I'm wrong , let's say I don't want to use the Slow Start feature for power up of the output, if I leave STSEL floating, it would mean that the SS feature would be disabled? 

2- If the previous statement is correct, what would be the default delay for the output ramp without Slow Start enabled? 

My issue is that the LMZ34002 is suitable for my needs, however the internal 10msec slow start is too slow for the power sequencing I'm planning in my current design. 

If it cannot be set below 10msec, is there any suitable alternate part that resembles the LMZ34002, besides the TPS84259, which is exactly the same but with different part number ? 

Kind Regards

  • Hello, 

    Please refer to the functional block diagram on page 5 of the datasheet. 

    There is a softstart capacitor inside the module. If you connect STSEL to the return (e.g. A_VOUT) you can utilize this provided capacitor. 

    If you leave STSEL floating, and provide external soft start capacitor on the SS pin, the part will use the external capacitor for the soft start timing instead of the internal one.