TPS92515: THERMAL PROFILE EFFICIENCY

Hello Gene,

Do you mean the efficiency of the buck converter drops by more than 5% or just the current to the TPS92515 IC? If it is the IC only I can see the bias current going up more than 5%. If it is the efficiency of the entire buck converter that is something else to check.

Best Regards,

Hi Irwin,

Thanks for getting back to me. See Temperature profile below:

TEMPERATURE (°C)	Vout (V)	Iout(mA)	POWER (W)
25	33.4	307	10.25
35	33.4	308	10.28
40	33.2	308	10.22
50	33.8	310	10.47
60	33.7	302	10.17
70	33.7	293	9.87
80	33.6	286	9.60

Note: Test was made at maximum dimming voltage.

We designed the board to be constant current at 310 mA. 

Referring to the table, at 80 °C, buck converter efficiency drops more than 5%.

Side note: we are using 1% resistors with 100 PPM.

Hello Gene,

Okay, the data you posted doesn't have to do with efficiency it has to do with current regulation set-point.  If the efficiency dropped the output power would stay constant and the input power would go up (which it will most likely do if the output power stayed constant).  Your issue appears to be current regulation versus temperature.

I am confused about the data above.  LEDs forward voltage tends to drop with temperature, Vout is going up in your data.  What is your load?

Can you look at the inductor current ripple when it is 25C and 80C.  Also, if possible, can you look at the peak current sense when it is at 25C and 80C?  What does your layout look like related to routing of the current sense resistor?  Do you have values for Viadj, Rcs/Rsense, Vin, Roff, Coff, inductor value (part number or datasheet) and any other relevant information to calculated your design.

Note, this is a current regulation issue, not efficiency.

Best Regards,

Hello Gene,

I haven’t heard back from you, I’m assuming you were able to resolve your issue.
If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

Best Regards,

Hi Irwin,

Thank you for your inputs. Sorry if I haven't gone back to you. I'm currently on a business trip and haven't tried the test yet. I'll get back to you as soon as I work on bench.

Note: The LED is not affected in the thermal profiling since it sits outside the oven. We will conduct a separate test evaluate it so that we can minimize the variables.

Regards,

Gene

Hello Gene,

Let me know when you have a chance to look at this.

Best Regards,