LMR16006: and LMR16030 fails very often

Hello,

Overvoltage failures could be a possible reason for the failures however it is hard to say for certain at this point. 

What are your desired operating conditions for both of these devices (input voltage range, desired output voltage and desired output current)?

What is the ambient temperature during operation?

Do you have any oscilloscope photos of the input voltage when the failures occur? I want to see if the input voltage is exceeding the absolute maximum rating of the device (65V).

Also could you share your schematic as well as layout and any photos of the broken devices? 

Regards,

Harrison Overturf 

Hello,

the big Problem on this issue is the fact that the bldc controller is made for RC raceboats. So i cant measure in the real enviroment.

And on the Desk i cant simulate a load of 4kW of Power.

Input Volatage: 2S to 10S Lipo (6.0V to 42.0V) for both DCDC's

The LMR16006 is used for internal 5V (some 3V3 LDO's and 12V Charge Pump all rated to max 5.5V). Current around 300mA-500mA

The LMR16030 is used for external Voltage 5V to 8.5V (controlled with DAC) and max. 3A

Ambient Temperature is max 50°C (measured near the Mosfest) but it should be the same for the whole PCB

On the Desk i have no Spikes at all. The Customer said:

Drivings with 20-30% (<50A) was no Problem. But with 50-60% (100-150A) the BLDC Controller stopped working.

So it could be Spikes comming from the Motor at higher load.

Please Note: i already changed the LMR16006 to the X Type. because i thought that the the min. on time could be to high with the Y Type

Hello,

Thanks for the background information. Are these failures coming from the field (i.e. being used in the RC race boats) or are you noticing these failures on your desk? It sounds like the customer is reporting the failures from the field but wanted to confirm. I ask this because I am wondering if physical vibrations in the end application are leading to the broken cases of the LMR16030.

What valued capacitors are you using on the input? The schematics don't mention the capacitor size but the layout appears to show input capacitors placed close to the converters (which is good). 

The diode in the LMR16030 schematic has a reverse voltage rating of 40V which is too low once you get up to the higher end of the input voltage range (42V with 10S Lipo). I would check to see if this diode is damaged. 

Also you mentioned that the batteries were directly connected to the input. Initially this made me concerned that perhaps there was a voltage spike when the system was turned on, but since you aren't seeing a spike on the bench and because you mentioned the failures are occurring after running for some time I'm starting to think the failures might be linked to the BLDC. Perhaps the BLDC is generating some back EMF that is causing the maximum voltage of the FB or SW pins to be exceeded. Do either of these pins appear damaged? Can you probe and check this on your desk?

Regards,

Harrison Overturf

Hello,
all failures coming from the field. On my desk i can't see any spikes.
The broken case dont seem to come from vibration (my guess). The one with broken broken case had a lot of destroyed parts around the 5V supply (LMR16006).

The Capacitors are 10µF 50V in 1206 Case.

Thank you for the hint with the 40V reverse voltage. I will change that to a 60V one. But this Diode i used together with the LMR16030. and this one just failed once.

On the last test our customer said the following:
"with 30-40% throttle (bldc Power) the was no problem. But with increasing Power to 50-60% the Controller stopped immediately."
on my desk i saw the knowing error: LMR16006 doesn't work (SW Pin doesn't switch) and some parts on the LMR16006 Output are also damaged.

So my actual guess is also spikes coming from the BLDC. Maybe its related to this Motor, maybe a mix of High voltage and Motor.

But how could i save the LMR160xx? Is there any App Note or ref.Design?

On some other commercial BLDC Controller i saw a protection with linear 300V bipolar Transistor and voltage Reference.

Hello,

Take a look at the attached app note. This document describes various methods of reverse battery protection circuits that you could use at the output of your buck to protect against any possible EMF surges. It is difficult to say whether back EMF from the motor is what is causing the failures because we don't have any scope photos of the event occurring, but trying some of the methods outlined in this documents will help to either prove or disprove whether back EMF is indeed the issue here. 

https://www.ti.com/lit/an/slvae57a/slvae57a.pdf

Regards,

Harrison Overturf