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I'm having trouble with a circuit that converts a low DC voltage (e.g. from a wall adapter) to a +/- 30V regulated supply. The circuit has a boost regulator (LT8330) followed by a dual supply inverting charge pump (LTC3260). Here's the circuit:

enter image description here

And the PCB layout: enter image description here

The spice simulation works as designed, however in reality not so much. The regulator (LT8330) circuit worked on the PCB, however the LTC3260 burnt immediately after connecting the supply. From the simulation there's some pretty large current spike at the Vin of the charge pump during start up which may be the problem. It's not clear to me from the datasheet how much this component can handle though.

Any help would be appreciated. Thanks.

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    \$\begingroup\$ One thing which you have learned from this is that you should use a current limited (set to max 50 mA or so) lab supply to power the circuit and check if it works properly. Now if anything is wrong a large current can flow (for example through L1 and D1) and destroy your IC. \$\endgroup\$
    – Bimpelrekkie
    Jan 12, 2017 at 15:03
  • \$\begingroup\$ As @FakeMoustache said, it's a good idea to use lab supplies for testing. A wall wart often uses poorly regulated transformers (30% or worse, even) and without much of a load can greatly exceed their spec'd output voltage. You need to know what you are working with and design for that. \$\endgroup\$
    – jonk
    Jan 12, 2017 at 17:17
  • \$\begingroup\$ In this case, it would be mostly for current limiting since the LT8330 is the one that sets the voltage for the LTC3260 and it worked. But still a lab supply would have been better. Thanks. \$\endgroup\$
    – gwolf
    Jan 12, 2017 at 20:07

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the LTC3260 burnt immediately after connecting the supply

R1 and R2 on the LT8330 set the output voltage by applying feedback to put nominally 1.6 volts on the FBX pin. Looking at the DS, it states that FBX may be as high as 1.632 volts. This means current through R2 could be as high as 37.95 uA. This current also flows through R1 producing a voltage across R1 of 31.31 volts.

In other words, the total voltage you may have at the output of the LT8330 regulator is 31.31 volts + 1.632 volts = 32.9 volts.

For the LTC3260, the operating maximum is 32 volts so you could easily be exceeding this. Absolute Maximum rating is 36 volts and so you are close to this limit and any transient behavior in the LT8330 (i.e. overshoot, ripple etc.) will tip the balance. Not to mention component tolerance - maybe you have 1% resistors for R1 and R2 that could be adding a further 2% to the problem?

In my opinion, you are driving the LTC3260 too close to the maximum limits.

Try setting the LT8330 to output a more reasonable voltage like 24 volts.

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  • \$\begingroup\$ Yeah, I have the bad habit of just looking at absolute max, but that's probably too close in this case. I can work as low as 25V output, so will try that (out of component though!) \$\endgroup\$
    – gwolf
    Jan 12, 2017 at 15:20
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    \$\begingroup\$ If this is because the wall wart output is 24 volts then why bother with the LT8330? \$\endgroup\$
    – Andy aka
    Jan 12, 2017 at 15:33
  • \$\begingroup\$ @gwolf if you haven't got any further questions or concerns about this answer, can you consider formally accepting it please? BTW, how did you go with your lower voltage circuit? \$\endgroup\$
    – Andy aka
    Jul 13, 2017 at 7:19
  • \$\begingroup\$ Lower voltage and checking with a proper lab supply (current limiting) did the trick. Thanks for the help! \$\endgroup\$
    – gwolf
    Jul 14, 2017 at 18:47

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