LDO problem in the PCB?

[madhu.b]

Hello,

In my PCB I have the problem with LD0 (MC78LC00). It has maximum rating of input voltage is 12V and its delivering the 3.3V as a output voltage. So, I am giving 12V as a input voltage and I am getting 3.3V of output voltage. After some time the gate driver is born off when I am voltage testing at the gate driver, at this stage the output pin of LDO is shroted to the ground pin of LDO. I dont know what happen..
So that I moved to another PCB and I soldered LDO and microcontroller after that I checked with mulitimeter at LDO pins which are giving 0V instead of 3.3V (means shorted). Then I checked on bread board which is giving exact 3.3V. And then I slodered the LDO with fly wires on PCB which is giving 3.3V as well. And then I slodered the LDO on PCB without any wires then its giving 0V instead of 3.3V (means output pin of LDO is shorted with ground pin of LDO)...

I would say that there is nothing wrong in my PCB design....

Please give solution why its happening...

 

[barry]

Gate driver? What gate driver? I thought you were talking about an LDO?

Just because you're getting zero volts doesn't mean it's shorted. Could it be in thermal shut-down? Did you actually measure the resistance to determine that it's actually a short?

 

[madhu.b]

Hello barry,

Now forget about the gate driver...
When I am checking with multimeter across the ground & Vout pins of LDO its giving beep sound and also showing some resistance between those pins. So, I could say that both pins are shorted... What I am saying is right???
Again I have a question about why those pins are shorted...

 

[barry]

If your reading 'some resistance' then it's not shorted!

The only way those pins can actually be shorted is if the device has failed, or there's actually a short on your board. Are you measuring the resistance with the device installed on the board? If so you, have to consider EVERYTHING that is connected to the device.

 

[madhu.b]

I havn't checked with the device on the PCB. Intially when I am placing the component on the PCB its giving exact 3.3V (This is the one actually the LDO has to deliverd), after some time its delivering the 5.7V or 8V something like that and after some time its delivering like 0V. After seeing these values I removed the chip and I cheked the connections on the PCB with multimeter then its giving beep sond on the Vout & ground pins of LDO. This is the problem actually I am facing....

 

[barry]

Sounds like you are damaging the regulator. What is your current load? Are you SURE you're limiting your input voltage to 12V? It's kind of bad practice to operate a device right at its absolute maximum rating (12V)

 

[sivamani]

Looks like there is a short on the board.Could you please measure the resistance between Power and gnd on the PCB after removing the LDO.

 

[madhu.b]

Current load is like 120mA... I think I was given the more than 12V as an input voltage given to the LDO..
If we are given more than the absolute maximum rating (12V) the regulator is damaged (I know this happens). Do you think that this might affect on the PCB (I mean in the PCB the ground and Vout pins are shorted right) ??

 

[barry]

Why don't you just MEASURE the PCB traces? How are WE supposed to know if your PCB is damaged?? If your LDO got too hot, it could definitely damage the board, but it would be pretty obvious. As I said before, you have to consider everything connected to the LDO. Also, not only did you have too high an input voltage, your load current is too high as well. You've got the wrong device for the job.

 

[madhu.b]

Ok thank you I will replace the component....

 

[sivamani]

Make sure that there is no short on the board before mounting new component..

 

[madhu.b]

I am sure that there is no short on the board...