one of my customers had a question as below, I need your help. Thanks a lot.
"I made a board to drive the 5W Halogen lamp. In the feedback resistor, I added one Trimmer to adjust the Vout in 4V~5.2V. The 5W Halogen lamp nominal is 5V/0.9A. Adjust the Vout will get the different current and brightness. In the no load condition, the Vout is normal. And I also use the High power LED to test the Vout. The current loading is from 200mA to 1.3A. The Vout is still good. But when I change to test the 5W lamp, the Vout can't be generated. It seems the TPS63020 is in some protection condition. I think this kind of Halogen lamp start up current may cause this problem. In the previous board version, I used the TPS63000 to make the similar design. But the function is correct. I would like to know if there is any solution can fix this problem. The circuit Vin is 5V/4A, Vout max current 1.8A. "
8547.balanced ls b.pdf
What is the cold resistance of the bulb? Please review the bulb datasheet. Also, please provide analog scope shots showing VIN, L1, L2, VOUT and IOUT of the TPS63020.
It is possible that the bulb looks like a very low resistance load to the converter and the 400mA softstart current is not enough to raise the output voltage past the required 1.2V for the current limit to increase. As a possible remedy, you could use a load switch to connect the bulb after the output has reached it's nominal voltage; though, the viability of this solution depends on the bulb's characteristics.
The customer replied as below:
"The attached files are the waveforms I captured this morning. Ch1: Vin, Ch2: L1, Ch3: L3, Ch4: Vout I don't have the current probe to capture the Iout.
About the Halogen lamp data, I only can find the related information about the inrush current from the bulb datasheet. There is no specific cold resistance or inrush current in the datasheet. I will check with bulb supplier about my current problem, too.
Could you draw the circuit to show how to use the load switch in this case? Thanks.
I don't see the attached files that you mention. I expect you to verify that the waveforms/schematic/layout match those of the TPS63020EVM-487. The load-switch would need to be connected between VOUT and the load.
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