LM5051: Surge protection question when configuring the LM5051 product circuit

PARK SANGHYUN

Part Number: LM5051
Other Parts Discussed in Thread: LM5064

The circuit was configured as above using the LM5051.

The power we need is -48V, 30A.

I want to design so that no interruption occurs during the 4kV surge test, but I want to know if the design of the front of the LM5051 is done properly.

Is there anything to reinforce? It is very difficult because it is the first power design.

After the above circuit, hotswap is configured using LM5064.

over 5 years ago

0 Karikalan Selvaraj over 5 years ago

TI__Genius 16305 points

Hello Park,

For protection during 4kV surge (2ohm impedance), schematic has MOV-14D820k which is expected to absorb the transient surge energy. The rating is 820V and 3500A peak surge current. Current rating is good to absorb 4kV surge (with 2ohm impedance, peak surge current is 2000A). But with surge applied, the voltage at 2000A surge current is going to be very high >1000V. This may damage the components which are not rated for such high voltage such as TVS which is 65V 2.5J energy TVS. We would like to know if these considerations are made in choosing the components. Basically we need to limit the surge voltage to within acceptable voltage level for LM5051, MOSFET, passive components in the power path.

Next, we also need to look hot-swap design to look at its over current protection during surge. Could you please share this portion of schematic as well?

Regards,

Kari.

0 PARK SANGHYUN over 5 years ago in reply to Karikalan Selvaraj

Intellectual 290 points

Thanks for the answer. Additionally, upload a hot swap schematic.
'Basically we need to limit the surge voltage to within acceptable voltage level for LM5051, MOSFET, passive components in the power path.'
How can I limit the surge voltage to within acceptable voltage?

0 Karikalan Selvaraj over 5 years ago in reply to PARK SANGHYUN

TI__Genius 16305 points

Hello Park,

Surge energy needs to be absorbed by MOVs at the input.

We recommend to select the MOVs based on 4KV surge pulse rating. At 4kV, 2ohm surge impedance, 2000A current could flow. Need to choose an MOV that clamps with 2000A with clamping voltage acceptable to LM5051. It can be more than on MOVs in parallel.

Let us know if you would be able to look up the MOVs selection:

There are a lot of application note and design notes around this topic in the web.

Couple of them i have shared here for reference:

https://m.littelfuse.com/~/media/electronics_technical/application_notes/varistors/littelfuse_selecting_a_littelfuse_varistor_application_note.pdf

https://www.electronicdesign.com/power-management/article/21800530/select-the-right-varistors-for-overvoltage-circuit-protection

Let us know if you were able to find correct MOV choice for 4KV surge protection which limits voltage on LM5051 to less than its maximum ratings.

Regards,

Kari.

0 Karikalan Selvaraj over 5 years ago in reply to Karikalan Selvaraj

TI__Genius 16305 points

LM5064 current limit or circuit breaker is set to 30A and this is good setting for turn off during surge.

Again, based on the references provided above, if the input voltage needs to be limited using MOV and TVS to less than 100V operating maximum of LM5051 and LM5064 rating.

Regards,

Kari.

0 PARK SANGHYUN over 5 years ago in reply to Karikalan Selvaraj

Intellectual 290 points

Thank you for your meticulous review and response.

Varistor was changed as shown in the attached circuit below, and an additional gas tube was used.
To summarize, I will use 48V 25~30A, and I want to keep the power ON without turning off the power when 4kV surge.
I think I can do the test with this implementation.

Thank you again.