LM5022: Thermal issue of short circuit condition

Wenhsiang Lin

Part Number: LM5022
Other Parts Discussed in Thread: LM51551-Q1, LM5060, BQ500100

Hi Team:

There is the thermal issue of LM5022 from RD feedback that during SCP and OCP condition cause fail and schematic as attached.

Vin:9~36Vdc , Vout:5V , Iout:4A ; 20W and OCP setup 110% =22W , when SCP test , secondary side current over 10A cause MOSFET damage and primary side LM5022(cycle by cycle current limit) and MOSFET damage also.

please help below question , thanks a lot.

1.Could we speed up LM5022 thermal shutdown function?(primary side)

2.Could you recommend external schematic of OCP ,SCP function for reference ?(secondary side)

3.How could we improve ? component level(MOSFET Qg?) ? FB ? switching frequency ?

tidrlp3.pdf

over 6 years ago

0 Richard Fu22 over 6 years ago

TI__Mastermind 31315 points

Hi Wenhsiang,

Thanks for using the LM5022. I cannot view your schematic- can you please reattach?

Thanks,

Richard

0 Wenhsiang Lin over 6 years ago in reply to Richard Fu22

Intellectual 520 points

Hi Richard Fu:

Upload , please check , thanks.

Regards / Mark

5086.tidrlp3.pdf

0 Richard Fu22 over 6 years ago in reply to Wenhsiang Lin

TI__Mastermind 31315 points

Hi Mark,

The LM5022 does not have hiccup mode, which one of our newest parts, the LM51551-Q1 has. Hiccup mode is a feature that will protect the converter in prolonged current limit conditions. You can see this in the datasheet here: http://www.ti.com/lit/ds/symlink/lm5155-q1.pdf

If you would like to use the LM5022, I've answered your questions below:

1) Could we speed up LM5022 thermal shutdown function?(primary side)

Ans: No, the thermal shutdown function is internal to the chip, and so it cannot be changed in the way you are asking.

2) Could you recommend external schematic of OCP ,SCP function for reference?(secondary side)

Ans: You can use an another IC, such as one of our eFuses with overcurrent protection. For example, I've listed the LM5060 with an external FET. I've also attached an application note that provides an external circuitry that you may find helpful: http://www.ti.com/lit/ug/tidubu0/tidubu0.pdf

3) How could we improve ? component level(MOSFET Qg?) ? FB ? switching frequency ?

Ans: Usually in the SCP/OCP cases, changing system parameters like the feedback resistors will not change performance here.

However you can do something with the switching frequency. A lower switching frequency will lower the average value of the primary side current so it could lower thermal losses. You could also size FETs and other components bigger such that they can meet the thermal requirements.

Thanks,

Richard

0 Wenhsiang Lin over 6 years ago in reply to Richard Fu22

Intellectual 520 points

Hi Richard Fu:

Due to price concern , RD will not to select LM5060 , please help below question , thanks a lot.

1.How is LM5022+ bq500100 ? need your help to recommend

2.RD also survey OP for OCP function , which P/N is more better for this case ? reference design ?

Regards / Mark

0 Richard Fu22 over 6 years ago in reply to Wenhsiang Lin

TI__Mastermind 31315 points

Hi Mark,

There are no current designs involving the LM5022 and BQ500100. If you're using it to power the BQ500100, as long as the LM5022 dc/dc converter circuit is designed properly for the electrical and thermal characteristics with added protection circuitry,I think it should be powered fine.

If your second questions is referring to over current protection, it would be best to look at the different kind of parts and reference designs TI offers here for OCP:http://www.ti.com/power-management/power-switches/products.html and http://www.ti.com/power-management/power-switches/reference-designs.html#search?famid=100

Thanks,

Richard

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LM5022: Thermal issue of short circuit condition