Is soft start necessary for a charge-pump?

[PaloAlto]

I have designed a voltage-doubler + LDO to raise the voltage level from 3.3V to 6V and supply the chip. I have not taken care at all about soft start. Should I be worry about it. I haven't seen any large voltage peaks in simulation. Can anyone explain me if this is something I need for my design and why?

Thanks

 

[safwatonline]

i am not sure but the name indicates that the output grows gradually which maintains all the (Vgd , Vgs, Vdb, Vsb) within the allowed limits.

what i am trying to say may not seeing large spikes is not the right thing to look for, instead monitor all the important relative node voltages.

 

[frankvh]

It largely depends on whatever is supplying current to your doubler, and what your current draw is expected to be. It's really a current discussion, not a voltage one. Softstart is useful in many switchers for limiting the initial inrush current. This has a few positive effects. It reduces (or eliminates) the chance of the upstream supply going into a shutdown or crowbar state due to excessive current draw. It can (depending upon how it's done) reduce overcurrent problems in the switcher. It can reduce EMI. If your upstream supply is another switcher, softstart can also be used to delay the turnon of your switcher, preventing it from trying to start up at the same time as the upstream switcher is also trying to get started (which can result in both switchers shutting down).

But really, it's all moot if your doubler is only drawing 10 mA and you've got a 1 amp linear upstream. Then probably none of that really matters.


Frank.
https://www.frankvh.com