Timeline for Why did the lmr51430XFDDCR get fried?
Current License: CC BY-SA 4.0
21 events
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| Sep 24 at 21:34 | comment | added | Robert | @TimWilliams Thank you very much for the help! It took me a while to understand the answer, but after going over it a few time, I think this has to be the problem in my circuit, especially since I use a ferrite bead at the input which also has an inductance. | |
| Sep 24 at 19:45 | comment | added | Robert | @InBedded16 Thank you again for all the help! | |
| Sep 24 at 19:42 | history | edited | Robert | CC BY-SA 4.0 |
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| Sep 24 at 19:23 | history | edited | Robert | CC BY-SA 4.0 |
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| Sep 24 at 18:54 | comment | added | InBedded16 | @Robert there probably isn't one, I was using the generic datasheet for that company's capacitors that comes up when you search the C24 part number. 25V should be sufficient but no harm in stepping up to 35V or 50V either. I would also strongly advise you to try to get those O-Scope captures before you redesign the PCB, without knowing which node(s) are behaving incorrectly you can't know if you're solving the actual issue or chasing a red herring. | |
| Sep 24 at 18:39 | comment | added | Robert | @InBedded16 thank you for the help! I will make another PCB with only the DC/DC converter and it's external circuit and I will use only components with much higher voltage ratings to see what I get. Also could you please send me a link to the exact datasheet for the C24? | |
| Sep 24 at 18:01 | comment | added | Hans mitm Flammenwerfer | @Robert I meant replacing 1µF with 2µ2F. If you don't want to remove the 1µF cap, you could solder another one ontop. | |
| Sep 24 at 16:21 | comment | added | Tim Williams | Consider this answer and the linked questions: electronics.stackexchange.com/questions/713381/… | |
| Sep 24 at 15:32 | comment | added | InBedded16 | @Robert interesting. Well you may want to pump those capacitors up to 25V ratings. Just because a capacitor is rated for 16V does not mean it is effective up to that voltage, the datasheet for C24 is a good example. Check page 14, it shows you that by 75% of the rated voltage the C_delta is 70%. So your input/output capacitors may not be doing much. I think your next step should be to gather oscilloscope readings for as many pins/nodes as you can measure and post/analyze them. | |
| Sep 24 at 15:24 | comment | added | Robert | @InBedded16 I've edited the initial post and I've added a list with all the parts. I have checked every component and each one is rated for at least 16V. I didn't follow the datasheet because I used the WEBENCH power designer from TI that made the schematic for me. | |
| Sep 24 at 15:19 | history | edited | Robert | CC BY-SA 4.0 |
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| Sep 24 at 15:10 | comment | added | InBedded16 | Also is there a reason you didn't follow the suggested values for 5V output as found on page 16 of the datasheet? ie R_fbt=100k and R_fbb=13.7k, and C_out = 2x 22uF caps? Your R_fbt is technically out of the recommended range, although I strongly doubt that is the root of the problem. | |
| Sep 24 at 15:07 | comment | added | InBedded16 | You haven't provided specs for your passives. Can you do that, or alternatively double check yourself that your capacitors are rated for the voltage they're being subjected to? | |
| Sep 24 at 14:47 | comment | added | Robert | @HansmitmFlammenwerfer do you mean to add a 2uF2 in parallel with C26 or to replace C26 with a 2uF2 cap? | |
| Sep 24 at 14:43 | comment | added | Robert | @InBedded16 I don't know if it's possible because I calculated a max current draw of 2.6A with 3 SG90 servos (750mA each) + MCU(stm32f405rgt6 + BMI088 + BMP280 and + external flash memory. Initially when I connected the battery the servos weren't even connected to the PCB. | |
| Sep 24 at 14:37 | comment | added | Hans mitm Flammenwerfer | Could you add 2µ2F on C26 and try again? | |
| Sep 24 at 14:33 | comment | added | InBedded16 | Is it possible the PCB has an inrush current that could cause the IC to fail on startup? | |
| Sep 24 at 14:27 | comment | added | Robert | @winny I've edited my question. The saturation current on the inductor is 6.6A. | |
| Sep 24 at 14:26 | history | edited | Robert | CC BY-SA 4.0 |
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| Sep 24 at 13:58 | comment | added | Robert | @winny The PCB is made up of 4 layers. The upper layer is signal, after GND, 3.3V and the forth layer on the other side is also signal. | |
| Sep 24 at 13:51 | history | asked | Robert | CC BY-SA 4.0 |