LM5122: Tranzistor protection

JIri Jicinsky

Prodigy 30 points

Part Number: LM5122

We use a 400W audio amplifier in one of our applications to increase the input voltage and drive the power.

The output power must be limited to approx. 400W. Limitation is done using resistors R280 + R290.

When I use Current sense common mode range, the sources turn off approx. 5s, then tries to turn on again. It's alright.

During the second turn-on sequence, a breakdown of one of the transistors T341, T342, T391, T392 occurs.

If I connect only one source, for example: I300 - everything is ok. the source turns off and on without a problem when overloaded. Transistors T341, T342 are not damaged.

How to prevent top transistors from being destroyed in a dual supply circuit?

5428.DAPA 351 c f.pdf

over 1 year ago

0 Haroon Wardak over 1 year ago

TI__Genius 10385 points

Hi There,

Thank you for using E2E forums, regarding your query could you please provide me the design specs for your schematic? Vin(min, typ, max), Vout, Iout and Fsw.

Thank you

BR,

Haroon

0 JIri Jicinsky over 1 year ago in reply to Haroon Wardak

Prodigy 30 points

Hi Haroon,

Vin 20V-35V

Vout - 58V

Iout - 7A

Fsw - 272kHz

Thank you

George

0 Haroon Wardak over 1 year ago in reply to JIri Jicinsky

TI__Genius 10385 points

Hi George,

Are you using these two LM5122's in Parallel? I do not understand from your description, I will take a look at the schematic, but due to my Bandwidth being narrow I can only get back to you on this middle of next week.

Hope this helps.

BR,

Haroon

0 JIri Jicinsky over 1 year ago in reply to Haroon Wardak

Prodigy 30 points

Hi Haroon,
Yes, we using two LM5122 parellel.

The problem occurs when connected in parallel.

1.single - 1xLM5122
when we use a single LM5122. Is the function of the LM5122 + other components in order. When the source is overloaded, it turns off and then tries to turn on. It's alright. All components are OK. The transistors are OK.

Device protection R291 - overcurrent is OK.
Overcurrent mode - Device off (5second), device on (approx. 0.5second), device off (5second), device on (approx. 0.5s); device off (5seconds); device on (approx. 0.5second)........
Transistor T341 + T342 - are OK

2. parallel - 2xLM5122
Device protection - overcurrent is OK.
Overcurrent R281 +R291 - Device off (5second), device on (approx. 0.5second), device off (5second), device on (approx. 0.5s);
On the second power-on attempt(in overcurrent mode). One of the transistors T341, T342, T391, T392 will be destroyed.

Please look at schematic.

Thank you

George

0 Haroon Wardak over 1 year ago in reply to JIri Jicinsky

TI__Genius 10385 points

Hi George,

Thank you for your reply, but after having a brief look at your schematic it seems that you are not using the interleaved dual phase boost configuration as instructed in the datasheet:

This may be the reason why you are facing issues. You can try to have a look at our LM5122 dual phase boost EVM as a reference.

Hope this helps.

BR,

Haroon

0 JIri Jicinsky over 1 year ago in reply to Haroon Wardak

Prodigy 30 points

Hi Harron,

red - wire as in picture 31.

purple - wire signals according to the LM5122EVH-2PH kit

I send progress to sig. SW1, SW2

DAPA 351 c f2.pdf

Best Regards

George

0 Haroon Wardak over 1 year ago in reply to JIri Jicinsky

TI__Genius 10385 points

Hi George,

I am sorry I am a bit confused by what you have said above. My point was why in your schematic do I see on the Secondary or Slave device the COMP, SS, SYNC_RT and FB not as it is in the datasheet and LM5122-2PH EVM users guide. Hope this was clearer.

BR,

Haroon

0 JIri Jicinsky over 1 year ago in reply to Haroon Wardak

Prodigy 30 points

Hi Haroon,
signals: COMP, SS, SYNC_RT, FB, UVLO - for circuit I300. Where do you think they are connected??

Best Regards

George

0 Haroon Wardak over 1 year ago in reply to JIri Jicinsky

TI__Genius 10385 points

Hi George,

In your schematic COMP, RES, SYNC_RT, SS, UVLO and FB pins of the Slave device are not routed correctly.

The COMP, RES, SYNC_RT, SS, UVLO of Slave device should be tied to the COMP, RES, SYNC_RT, SS, UVLO of the Master device and FB of Slave device should be pulled up to VCC. That is why I shared the LM5122 2PH EVM user's guide so you could see how the connections are done.

Hope this helps.

BR,

Haroon

0 JIri Jicinsky over 1 year ago in reply to Haroon Wardak

Prodigy 30 points

Hi Haroon,

I am sending you the schematic so that you can see the real connection between Master and Slave.
Brown labels are automatically linked to the same name. 
Components marked with .NC - mean not connection.

DAPA 351 c f3.pdf

BR
George

0 Haroon Wardak over 1 year ago in reply to JIri Jicinsky

TI__Genius 10385 points

Hi George,

I see, but for SS of the Slave you still have C353 without NC and SYNC_RT of Slave R354 without NC, remove those you do not need them. Also, for RES C362 no NC, so remove that as well. Also C274 should also be NC I think. Please cross check your schematic with the EVM's schematic

Hope this helps.

BR,

Haroon

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LM5122: Tranzistor protection