LM5069: LM5069 is very easy be damage when 4kV surege test

Betty Guo

Part Number: LM5069

Hi,

customer to the 4kV surge test on the LM5069, found thath the LM5069 and MOSFET will be very easy demage. they add the TVS on the out pin, the clamp voltage is 75V. in the datasheet, the maximum voltage of VIN is 80V. the TVS part number is SMDJ85CA。

below is the schematic: add TVS on the between OUT pin and GND.

could you give some suggestions, thank you

over 5 years ago

0 Rakesh over 5 years ago

TI__Guru** 105531 points

Hi Betty,

What is the source impedance of 4KV surge test?

Best regards,

Rakesh

0 Betty Guo over 5 years ago in reply to Rakesh

TI__Expert 7300 points

Hi Rakesh

the impedance is 15ohm

0 Betty Guo over 5 years ago in reply to Rakesh

TI__Expert 7300 points

Hi Rakesh,

Add more information. The damage pin is PIN1 and PIN2 of LM5069.

Then connection of surge source is below red arrow :

0 Rakesh over 5 years ago in reply to Betty Guo

TI__Guru** 105531 points

Hi Betty,

To support surge test, LM5069 should be configured with back-to-back MOSFET and diode in the device ground path as shown in http://www.ti.com/lit/an/snva683/snva683.pdf

Then, input TVS needs to be sized to absorb the surge current (4kV/15Ohm = 266A) while keeping the TVS clamp voltage with in 100V (abs max voltage of LM5069). Using Two 30V TVS diodes (such as MPLAD15KP30CA) in series would be able to handle large current.

BR, Rakesh

0 Betty Guo over 5 years ago in reply to Rakesh

TI__Expert 7300 points

Hi Rakesh,

some quesitons:

1. customer add surge source on the output of the LM5069, it is the different with the snva683. Can they use the same circuit of figure 5 shown in the snva683?

2. they found that in the snca683, there have two ground in the LM5069, how to connect these two ground?　In customer application, only one ground.

thank you

0 Betty Guo over 5 years ago in reply to Rakesh

TI__Expert 7300 points

Hi Rakesh,

one more question is the total impedence of surge rouce is 40ohm, not 15ohm

0 Rakesh over 5 years ago in reply to Betty Guo

TI__Guru** 105531 points

Hi Betty,

1. customer add surge source on the output of the LM5069, it is the different with the snva683. Can they use the same circuit of figure 5 shown in the snva683?

Though we never tested, it should work even for surge on the output side. In that case, add TVS diodes at the output side

2. they found that in the snca683, there have two ground in the LM5069, how to connect these two ground?　In customer application, only one ground.

The device ground is a virtual reference for all the components around LM5069. This node is connected to the system ground through the diode D1 (refer Figure-5 in snva683). Please refer EVM user guide for layout reference http://www.ti.com/lit/ug/slvuaa1/slvuaa1.pdf

3. the total impedence of surge rouce is 40ohm, not 15ohm

In that case, use two 5.0SMDJ30A TVS diodes in series

BR, Rakesh

0 James Zhan over 5 years ago in reply to Rakesh

TI__Expert 4365 points

Hi Rakesh,

This is James Zhan, I'll support this customer from now on since Betty is moving to another team.

1. Since snva683 is for the input side, could you please share a schematic for the output side surge? They don't have the back to back FET here.

2. Without changing the PCB right now, do you have any suggestions for customer to run the test of this two ground thing?

Rakesh said:
The device ground is a virtual reference for all the components around LM5069. This node is connected to the system ground through the diode D1 (refer Figure-5 in snva683). Please refer EVM user guide for layout reference http://www.ti.com/lit/ug/slvuaa1/slvuaa1.pdf

Let me know if you have more advice, thanks!

0 Rakesh over 5 years ago in reply to James Zhan

TI__Guru** 105531 points

Hi James,

Below minimum modifications are needed to protect the LM5069 during surge event.

Diode D1 in the device return path as shown in Figure-1 in snva683
Bidirectional TVS at the output to clamp transient voltages with in 100V (abs max votlage of LM5069)

BR, Rakesh

0 Rakesh over 5 years ago in reply to Rakesh

TI__Guru** 105531 points

Hi James,

Closing here as we are discussing customer requirements over email.

BR, Rakesh

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LM5069: LM5069 is very easy be damage when 4kV surege test