My LT3045 doesn't work

Hi,
the foremost question is the voltage at the set pin.
Please provide necessary information.

Hi Alexxx,

I checked the board again but some thing has changed. Both the output voltage and the votage at the SET pin now are 0V. 
I also try to the second board, without installing the load circuit. And both the output and SET pin voltages are 0.64V.

The voltage at the SET pin are almost 0V in 2 cases, means the SET current are also 0uA, so are the 2 LT3045 damaged?

I'm puzzled by this issue and would appreciate any insights

Best regards,
Tuan Tran

Hi TuanTran,
There are two possibilities:
- The LT3045 is damaged - most probable now: "I checked the board again but some thing has changed. Both the output voltage and the votage at the SET pin now are 0V"
- Rset has a short or is maybe 1 /1000 value it should be.
Use an Ohmmeter to check Rset. If it is much too small, desolder LT3045 and measure again.
Also try a little load - 1 mA is enough.
It could be also some strange layout problem.

Hi Alexxx,

I have removed all components surrounding the LT3045, including resistor Rset and capacitors for measuring. All measured values are correct.

After this, I'm still observing 0V at both the output and the SET pin.

Given that the components are sourced from reputable suppliers like DigiKey and Mouser, I believe the issue lies elsewhere.
I will try to check the PCB again.

Thanks for your suggestion.
Tuan Tran

Hi Alexxx,

After removing all components around the LT3045 and carefully inspecting the PCB for any issues (none were found), I reassembled both boards with all new components. Both boards initially functioned as expected, although the output voltage was slightly lower than 5.00V, likely due to the 1% tolerance of the 49.9kΩ resistor.

To address this, I replaced the 49.9kΩ resistor on the first board with a 0.1% accuracy resistor. However, after this replacement, both the output voltage and the voltage at the SET pin of the first board unexpectedly dropped to 0.6V.

The second board, which still uses the 1% resistor, continues to function as expected.
I also checked all capacitors and resistors around the LT3045, but nothing unsual found.
Further investigation revealed voltage fluctuations on the output, ranging from approximately 0.6V to 1V, as observed on an oscilloscope.

I'm puzzled by this unexpected behavior and would appreciate any insights.

Best regards,

Tuan Tran