HI,

I have used the following 12V to 5V regulator. The part number is A6986F5V (STMicroelectronics). Problem is in 5 boards I designed and assembled I am getting different voltage outputs from the regulator ranging from 5.1V to 5.92V. But in my application, the maximum voltage I can accept is 5.2V. Please let me know what could be the reason for the extra voltage generated. Could it be soldering issue or any other problem with design.

 

You measure produced no load? Connect the output 5V resistor. Example 470 ohms.

 

You measure produced no load? Connect the output 5V resistor. Example 470 ohms.

HI,
But in some boards I am getting exact 5V with same setup. In my board this 5V is fed to 2 controllers. So they will be the load.

 

Are you sure your IC is not a fake, or reject?

 

What resistors have you got on pin 9 to set the output?

Get yourself a proper regulator like a Lm2596...

 

Get yourself a proper regulator like a Lm2596...

I was going to mention that but figure the OP had some special need for that chip. It seems like a way overly complicated chip. Those ones from TI are so easy to use.

 

HI,
But in some boards I am getting exact 5V with same setup. In my board this 5V is fed to 2 controllers. So they will be the load.

Why don't you add a load an measure it? What is the harm? It should be tested that way ayway.

 

What resistors have you got on pin 9 to set the output?

My thoughts exactly... Don't see how you could get more than 0.85V because you're feeding back the output voltage.

 

Are you measuring the output with a digital voltmeter, or something else? It could be that the output is just very noisy, and you are picking up the peak voltage of the noise. I would use a ceramic capacitor, not aluminum electrolytic, for C18, as it appears that your switching frequency is 500 kHz. If you cannot change C18, at least put some kind of ceramic capacitor with as short leads as possible between the FB pin and the SGND pin. 0.1 uF is better than nothing, but if you can do 10 or 22 uF, so much the better. Also, if L5 is a purchased part, is it suitable for this application?

 

What resistors have you got on pin 9 to set the output? ...

He's using the part with the 5V suffix, so I assume the voltage is automatically set internally?

 

Well its not working

 

I have seen the book, which the author described a similar case. He used a foreign regulator in its tester. In the study, he found work at the output of the stabilizer generation. He addressed to the author of the stabilizer and learned that a stabilizer designed for the current of at least 200mA. So I suggested to connect a resistor. In one my tester LM317 stabilizer is made at low output voltages 1.3V instead gave voltage 1.5V. When you hook up the load voltage becomes 1.3V.

 

Well its not working

That much is certain.

 

HI all,
Thanks for your reply. My end application is going to be automotive which requires several protection such as load dump, over voltage protection, load and line regulation, soft start etc. And the most important thing is my Regulator must be AEC qualified which is the reason I chose the following part A6986F5V. I feel it is only the IC problem as I faced that issue of output voltage going to 5.96V in only one of my boards. The rest of the boards are giving proper 5.0V,.5.1V.

 

Are you measuring the output with a digital voltmeter, or something else? It could be that the output is just very noisy, and you are picking up the peak voltage of the noise. I would use a ceramic capacitor, not aluminum electrolytic, for C18, as it appears that your switching frequency is 500 kHz. If you cannot change C18, at least put some kind of ceramic capacitor with as short leads as possible between the FB pin and the SGND pin. 0.1 uF is better than nothing, but if you can do 10 or 22 uF, so much the better. Also, if L5 is a purchased part, is it suitable for this application?

HI Roderick,

Yes currently C18 is a tantalum cap. I will try changing it to ceramic 10uF and check if it helps. And the inductor I have chosen is AEC qualified. So I hope that doesn't create a problem.

 

Why don't you add a load an measure it? What is the harm? It should be tested that way ayway.

Yes I will try putting a 470ohm resistor and check. Thanks.

 

What resistors have you got on pin 9 to set the output?

Get yourself a proper regulator like a Lm2596...

HI,
Pin9 is actually the feedback pin. THis is a fixed voltage regulator so I am not setting any resistors as per the reference design in daasheet.

 

Please find the datasheet attached.

 

Hi all,

Great news.!!!! Solved the problem. Was just a soldering issue. My bad. I guess the thermal pad of the regulator (SGND) was not properly soldered to the pad. I resoldered it with an IrDA machine and it fixed the problem. I am getting a clean output voltage of 5.02V. Seems like the issue was the floating GND was acting as a fault trigger to shoot up the voltage to 5.89V. thank you all for your suggestions.

 

Good that you solved the problem.