TPS54160: TPS54160

HI

Can you show the schematic and what is the catch diode? can you help check whether you have over voltage happened? and can you show us the SW waveform in full load condition?

Thanks

hi, thanks for your replay

so as i said , input voltage is fixed 55v (you can see it rise value ,marked as blue in the scope image) no over voltage has been spotted.

another important question is : could you also tell me, if input voltage is 55v , why i see switching frequency on the catch diode (marked as yellow in the scope image) is 8v below - i measure 47v. 

thanks again my friend.

itzik

yeah i understand my friend, but because of covid-19 , i can't reach to the lab to test it, as soon as i could , i will do the test for you.

i need your help with trying to see if there is a problem n schematic and most inmportant, try to explain the 8v difference between vin on the voltage on the catch diode.

thanks

itzik

HI

1. it may caused due to low resolution of scope, you may need use high bandwidth with short time .

2. is the blue voltage is PIN2 VIN voltage or voltage at main?

Thanks

blue is vmain , it is the voltage presented in pin2. i check rise time. the voltage supplied is 55v.

yellow is voltage on catch diode. it is the voltage presented on pin10. i check switching voltage. the voltage i measure is 47v.

why there is a difference ? as i check for internal components on the IC , i think that catch diode need to have same voltage as vin , or am i wrong ?

hi

the picture i have attached is an old picture, i don't have new one , because i can't reach to the lab to test it and show you. but i measured it before as you said , with higher resolution, and same ground. and got the voltages i mentioned in the previous comment. the question is, if i supply 55v in pin 2, what voltage i need to get in pin 10 ? 

thanks

HI

you should get a around a 55V voltage, should not have 7V voltage gap between PIN2 and PIN10.

Thanks

hi

maybe it is related to the BOOT-PH parameter ? do you think you can realize from design schematic or from TI theory , why it could happen ?

thanks

HI

Boot-PH voltage will let you have +5V~+8Vthan Vin voltage , not -5V~-8V. but if boot-ph voltage low, it may cause high side can't turn on. normally, output and SW  will be unstable.

I still think we need a clear waveform of VIN PIN and SW PIN to figure out the issue.

Thanks

hi

please write me exactly what you need from me, which waveforms, which bandwidth on which legs and i will get it for you tomorrow

thanks

HI

pls test the waveform at VIN PIN and PH PIN with light load and heavy load. keep 5-10 switching cycles in one screen.

Thanks

LIGHT LOAD

HEAVY LOAD

HI

The votlage looks right compare VIN and SW PIN,

The SW looks have some jitter, can you help remove the cap at RT PIN see any improve? normally we don't put capacitor at RT.

and pls test whether have input votlage spike which may make the devie and diode damage. and in the same time, pls help check the temperature raise of IC and diode.

Thanks

i have checked again

probably , sent you wrong test setup

i am attaching the right picture now.

check the voltage difference (yellow is VIN, blue is PH voltage)

thanks

HI

pls check the scope setup, you can try full bandwidth or you can check at EVM first.

If VIN PIN and SW has 7V voltage gap, when the duty on, the mosfet have 7*0.2A=1.4W power loss when high side is on if load current is 0.2A. can you help check the efficiency or thermal of chip, if thermal or efficiency meet the datasheet, it may cause by scope.

Thanks

hi

i have checked efficiency and it is according to datasheet. also i checked with several scopes , several probes and several boards. got same results. i am attaching the PH against VIN scope image with more accurate test setup in full bandwidth , with some measurements . maybe you could help me realize why i get lower voltage (48v) on PH then VIN (55v) ???

HI

what is the load condition? if you low down the input votlage to 48V or 24V , is SW still have 7V voltage difference or it only happened in high voltage?

and if you add the input votlage after the common choke, any change?

Thanks

hi

it was a scope issue.

now, could you help me to see if the design is ok ?

thanks

Hi

the schematic is OK.

pls follow the layout guild line in datasheet.

Cause diode current is low, the most possible way cause diode damage is over voltage. so one potential cause is when you applied 55V too quick to system, the input L and C will have some resonant cause the input higher than max voltage.

Thanks

hi

i have checked the system for 2 weeks with extreme temperature range , with high input voltage , change loads to get input voltage transients etc. but the most high input voltage overshoot I got was about 200mv higher. all the experiments I did and I couldn't create overvoltage on the diode, so i thought maybe something is hidden in design that cause the diode to fail.

any other ideas ?

thanks

Hi

if you know when the circuit damage (start up, transient or shutdown) we maybe can find a way to identify the issue.

In these two weeks, do you find any diode damage in your debug?

Thanks

this is the problem, i didn't find any reason in which the voltage will be higher than the input voltage in any scenario