I am using MIC29302UW IC for converting 12V to 3.8V. I am using this IC from last 2 years and have used this LDO in more than 50 devices. But the same IC is not working in my new PCB board. I even made a small PCB, only for testing the working of MIC29302UW,but its not showing the correct output.


Let me explain the issue- I am providing 12V at the input of MIC29302UW and using 100k(R1) and 47.7(R2) resistors to form feedback loop. But instead of getting 3.8V(approx.), its showing 12V at the output pin. The input voltage is not stepping down from 12V to 3.8V.
So, what i can do to rectify this error and make it working? I have bought this LDO IC from DIGI-KEY. So, i am hoping that there is no fault in the IC.



NOTE: I am using the original MIC29302UW from DIGI-KEY.

 

Have you read the minimum load current part of the datasheet ? The resistor values you have used used in the potential divider to the adjust pin are far higher than in the example in the datasheet.

Les.

 

Have you read the minimum load current part of the datasheet ? The resistor values you have used used in the potential divider to the adjust pin are far higher than in the example in the datasheet.

Les.

If that doesn't fix the problem, what is the voltage on the ADJ pin?

 

On the ADJ pin of MIC29302UW, it showing 3.8V.
" The resistor values you have used used in the potential divider to the adjust pin are far higher than in the example in the datasheet. "
I have used the same resistor value in my previous board design and its working fine.

 

Did you add a load to the output which draws at least 10mA at the desired output voltage (3.8V/10mA = 380Ω maximum)?

 

Did you add a load to the output which draws at least 10mA at the desired output voltage (3.8V/10mA = 380Ω maximum)?

i connected a led at the output

 

That answer does not answer the question unless you tell us the value of the resistor in series with the LED and the colour of the LED. (Different coloured LEDs have different forward voltages so we need that information to work out how much current you were drawing from the output.) Also was the 3.8 volt reading with the meter probes directly on pins 3 and 5 of the MIC23902UW.

Les

 

That answer does not answer the question unless you tell us the value of the resistor in series with the LED and the colour of the LED. (Different coloured LEDs have different forward voltages so we need that information to work out how much current you were drawing from the output.) Also was the 3.8 volt reading with the meter probes directly on pins 3 and 5 of the MIC23902UW.

Les

I have used 330 ohm resistor with red led.
"Also was the 3.8 volt reading with the meter probes directly on pins 3 and 5 of the MIC23902UW."
----That's correct, i was getting 3.8V at pin5 and pin3 when tested it with meter

 

If you are not prepared to do the tests as requested then it is difficult to help you. Albert asked you to apply a load of at leas 10 mA. Your LED in series with a 330 ohm resistor did not do this for the designed output of 3.8 volts. If the ouput voltage did not change at all then the problem is probably not the minimum load problem, I suspect you may have a fixed voltage version of the regulator, a faulty regulator or your new board layout is not the same as the schematic. I suggest removing R9 or R10 so that the regulator is trying to regulate close to it's reference voltage. (Which should be about 1.24 volts for the variable output version.) It may be a little different with the 100K resistor still in circuit. Measure the voltage on the output AND pin 5 with respect to pin 3 and report the result.

Les.

 

If you are not prepared to do the tests as requested then it is difficult to help you. Albert asked you to apply a load of at leas 10 mA. Your LED in series with a 330 ohm resistor did not do this for the designed output of 3.8 volts. If the ouput voltage did not change at all then the problem is probably not the minimum load problem, I suspect you may have a fixed voltage version of the regulator, a faulty regulator or your new board layout is not the same as the schematic. I suggest removing R9 or R10 so that the regulator is trying to regulate close to it's reference voltage. (Which should be about 1.24 volts for the variable output version.) It may be a little different with the 100K resistor still in circuit. Measure the voltage on the output AND pin 5 with respect to pin 3 and report the result.

Les.

" Your LED in series with a 330 ohm resistor did not do this for the designed output of 3.8 volts. "
-- My circuit is working now.
The problem was in led. The led was defective. I changed the led and kept all the connection as i have mentioned in my question and now its working.
The issue was due to minimum load condition.
Thanks for your help and support