LM5066: GATE pin is not working after the output is shorted and come back to normal

Hi Chase,

Can you share below details to debug

1. Test waveform of Vout, Timer, GATE and input current during short circuit test.

2. Filled up design calculator

3. What is the startup load at the output ?

Best Regards, Rakesh

Hi Rakesh,

Here is more information you asked;

1. during short circuit test, Vout, Timer, GATE are 0V, and initial input current is 1.6V

2. here is design calculator;

LM5066 Design_Calculator_REV_B_0317.xlsx

3. startup load current is 1.6A

and here is some values of parts

Rsns = 12Mohm

Rpwr = 150Kohm (calculated value was 30Kohm based on datasheet, but it did not work so they found another value)

Ctimer : 150nF

MOSFET : FQD13N10LTM (Fairchild)

as i said, overcurrent protection works well(insert 52V/2.2A->output stopped) and it come back to normal when overcurrent is over.(2.2A to 1.8A)

and customer wants the input voltage 50~53V, input current 0A~1.8A. also they want short circuit protection and overcurrent protection.

Please check this issue. Thanks.

Best regards,

Chase

Hi Chase,

Is customer using dvdt circuit at the GATE as shown in the schematic ? If yes - set F72 cell in the design calculator to 'YES'

Test waveform of Vout, Timer, GATE and input current during short circuit test is missing, please get it.

Best Regards, Rakesh

Hi Rakesh,

Thank you for your reply.

during short circuit test, these 3 waveforms are just 0V. is waveform picture necessary in this situation?

and here is my modified design calculator, changed F72 to 'YES'.

LM5066 Design_Calculator_REV_B_0317-2.xlsx

if there anything wrong, please let me know.

Best regards,

Chase

Hi Chase,

Waveform is still needed to understand the timer voltage, current profile during the fault.

Hi Rakesh,

please check the waveforms below ;

CH1 yellow : GATE

CH2 red : Vout

CH3 blue : Ctimer

CH4 green : Iout

as you know, this IC is completely dead after each short test. this test is a huge burden for my customer.

please check this issue. Thanks.

Best regards,

Chase

Hi Chase,

Please suggest above changes to the customer and let us know if there are any follow-up questions.

Best Regards, Rakesh

Hi Rakesh,

Thank you for your reply.

I already guided your suggestion right after your reply.

I will tell you if there are any updates from my customer.

Best regards,

Chase

Ok Chase

Hi Rakesh,

It took a long time to get the parts for test.

the result is, it is all the same even I changed FET and diode, waveform is same too.

could you tell me other points to check?

also I want to tell that when LM5066 is broken because of the short output circuit, PCB routing in front of SENSE pin (#3) burns out.

I think it is related on this matter.

please check this issue. Thanks.

Best regards,

Chase

Hi Chase,

You mean LM5066 failed even when you used PSMN4R8-100BSE for Q15 and TVS diode 5.0SMDJ54A at the input  ?

Please share waveforms (similar to Figure 46 and Figure 47 in www.ti.com/.../lm5066.pdf) during short output test

Best Regards, 

Rakesh

Hi Rakesh,

Thank you for your reply.

fortunately they solved the problem themselves. it was because of the L3 inductor.

after removing L3, hot-short protection is working well.

and still I have another question.

they use pin7 as enable(shutdown control)

they tested it many times about it, sometimes it is working even EN is not high.

in this situation they have to toggle EN pin in GUI. then it work properly. until then it is always working even they change the status of EN pin.

is it a problem of schematic? or the matter of I2C communication or other SW part?

please give me some advice about this matter. Thanks.

Best regards,

Chase

Hi Chase,

EN pin voltage has to be HIGH to turn-ON the external FET.

Have they probed pin-7 voltage and GATE voltage to confirm ?

Best Regards, 

Rakesh

Hi Rakesh,

Yes, PIN7 is low, and GATE pin is high.

and I have one more question.

If i want to use pin7 as enable, should I refer the schematic in datasheet 8.4.4? (with 3 resostors)

actually we used 4 resistors to set UVLO and OVLO. is it okay to control the shutdown?

Best regards,

Chase

Hi Chase,

Yes, PIN7 is low, and GATE pin is high.

-> Is it the same case for all the boards ? When you replace with new IC and new MOSFET on the same board  - is it fine ?

If i want to use pin7 as enable, should I refer the schematic in datasheet 8.4.4? (with 3 resostors)

actually we used 4 resistors to set UVLO and OVLO. is it okay to control the shutdown?

->The control to shutdown the device with UVLO/EN = LOW is independent of single resistor ladder or two separate resistor ladders.

Best Regards, 

Rakesh

Hi Rakesh,

Is it the same case for all the boards ?

-> actually it depends on the time, even in the same board. sometimes it works correct, sometimes it does not work correct.

When you replace with new IC and new MOSFET on the same board  - is it fine ?

-> they did not try it, just I can imagine that it depends on time.

can you tell me the points to check more for this matter?

Best regards,

Chase

Hi Chase,

It's very difficult to comment if the behavior is not repeatable and depends on time. Can we place oscilloscope in trigger mode to capture (GATE, input current, timer voltage, EN voltage) at that instant.

Best Regards, 

Rakesh