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I simply don't know what I'm doing wrong... I'm trying to use LMR62421 boost converter (schematic) and I'm trying to boost Li-Po battery voltage levels to 9V. I just copied the schematic from example from datasheet and created the PCB, and getting short circuit problems when I connect my PSU. When PSU is not connected and I go through circuit with my DMM I cannot find a short...

Schematic PCB PCB Front side PCB back side

I've highlighted rather ugly looking connection in red circle just to clarify this ugly soldering job...

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    \$\begingroup\$ Do you have 10 uH and A of saturation current in that green thing? Also, what diode is that? \$\endgroup\$ – winny Jun 5 '17 at 21:53
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    \$\begingroup\$ Are you sure that's an inductor and not a 10R resistor? \$\endgroup\$ – Trevor_G Jun 5 '17 at 22:00
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    \$\begingroup\$ Even if it is an inductor, what's the current rating on it? \$\endgroup\$ – winny Jun 5 '17 at 22:04
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    \$\begingroup\$ INductor probably shorts then things fry quickly \$\endgroup\$ – Trevor_G Jun 5 '17 at 22:25
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    \$\begingroup\$ pound to a penny it's the inductor won't handle the current. Once in saturation, it looks like a short circuit. Look at photos of SMPS converters, you never see that style of inductor used, I wonder if there's a reason? \$\endgroup\$ – Neil_UK Jun 6 '17 at 5:03
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First off, you probably want a schottky diode rather than a standard diode. Sounds silly, but that can make a massive difference I have found. Secondly, with all these types of boost converters, PCB payout is absolutely key. You probably want your input and output capacitors much closer to the chip. You can also try sticking a load on it, as some of these require a minimum load to startup (on the first page of the datasheet it shows that the efficiency is poor under light loads).

The next thing to do is figure out how much current you are expected to pull from that thing and ensure your components can take it. If it is estimated to be a large current (this thing says it can do up to 2.1A) then you might want to make sure you have enough ground. You just have a small track, and most of these chips need a nice amount of ground plane to dissipate heat in order to work correctly.

How did you come up with 10uH as your inductor value by the way? Another thing about the inductor, the datasheet mentions that ferrite based inductors are preferred, due to perating frequency. Did you ensure to go along with that? And your capacitors, with these types of chips, you want capacitors with low ESR (equivalent series resistance).

I think this issue may be simply down to the PCB design aswell as component selection. It has happened to me before. Hope this helps.

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