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# overshoot of LTC3440?

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#### muoinhohn

##### Full Member level 2
Hi all
I use LTC3440 with boost topology to convert from 3.7V to 5V.
I made a circuit like in LTC 3440 datasheet (page 16). But when i simulate it with SwitcherCAD, I get one overshoot 9V at the start-up moment with a settle time is 0.4ms.
With overshoot 9V, it is important. How do i make to reduce this ?

#### v_c

Sounds like you might want to adjust the soft start capacitor and resistor. I believe that is te Rss and Css capacitors tied to the $\bar{SHDN}/SS$ pin. You might want to slightly raise the Rss and/or Css values to see if this will limit the peak for you.

Best regards,
v_c

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### muoinhohn

Points: 2

#### muoinhohn

##### Full Member level 2
Hi
It's ok. Now the overshoot is 5.15V. It is acceptable.
muoinho

#### v_c

Great! I am glad it worked -- did you just adjust the soft start resistor and capacitor? Sometimes you have to ramp up the dc voltages for the IC to kick in. There is an option in LTspice to ramp the sources. By the way, since you are using LTspice I should mention a few things.

1. There is a very nice LTspice Yahoo! group that you should consider joining (if you have not done so already). The people there are very nice and the original developer of the software read the group as well (Mike Engelhardt) -- he is extremely knowledgable. I have not visited the user's group in a while but in the past they have been very helpful.

This file contains lots of material including a presentation on LTspice made my Mike. It also includes a directory called "jigs" which has a test circuit for nearly all of the ICs that Linear Technology makes. In most cases, the circuit that is setup in these "jigs" or test setups is the example circuit that is mentioned in the datasheet. So you may find this extemely useful to get a circuit simulation started.

Best regards,
v_c

#### muoinhohn

##### Full Member level 2
Hi
Yes, I joined LTSpice group and found much helps about LTSpice.
Best regards
Muoinho

#### ferrite

##### Member level 1
yes, that user group is very good. but i donot know about the handout thing. i just downloaded, very nice. thank you for the nice piece of info

v_c said:
Great! I am glad it worked -- did you just adjust the soft start resistor and capacitor? Sometimes you have to ramp up the dc voltages for the IC to kick in. There is an option in LTspice to ramp the sources. By the way, since you are using LTspice I should mention a few things.

1. There is a very nice LTspice Yahoo! group that you should consider joining (if you have not done so already). The people there are very nice and the original developer of the software read the group as well (Mike Engelhardt) -- he is extremely knowledgable. I have not visited the user's group in a while but in the past they have been very helpful.

This file contains lots of material including a presentation on LTspice made my Mike. It also includes a directory called "jigs" which has a test circuit for nearly all of the ICs that Linear Technology makes. In most cases, the circuit that is setup in these "jigs" or test setups is the example circuit that is mentioned in the datasheet. So you may find this extemely useful to get a circuit simulation started.

Best regards,
v_c

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