TPS61196: The output strings randomly turn on

Hi Danilo,

I would suggest customer capture the voltage waveforms of IFB1~IFB4 during start up. For now they set the VLED_SHORT threshold as ~1.85V, so I want to know during start up will some IFBx voltage over this threshold.

BR

Patrick

Hi, Thanks for the fast response. After further investigation we found out the issue was due to the broken cable..... 

I would like to ask you to review the following output voltage ripples, measured right on the output caps. The ripples look a bit strange with a max peak of 3V which is quite a lot. The boost supplies four LED strings each consumes 80mA,with a voltage on the common Anode of 46.5V. I am attaching two cases with 2x10uF output capacitors and a case where a100uF output cap is used. In both cases the switching frequency is 400Khz. 

1. 2x10uF output cap.

2.1x100uF output cap.

Please share  your thoughts! 

Thanks

Hi,

I think 2x10uF might be too small capacitance for your application because of the DC variation.

Could you please capture the waveform of SW, Vout and input PWM together?

BR

Patrick

Hi Patrick,
I got the results but unfortunately not all together. 

1. On this picture, the yellow signal represents the SW, where the blue one is the output AC, with a spikes of close to 2V. The frequency is set to 400Khz, and the output capacitor is 100uF.

2. On this picture both output and the PWM are shown, for the same configuration as pic1. 

3. I added just a 100nF MLCC cap, next to the 100uF and here are the results of the output. The output seems to be smoothened and the ripple is about 200mV or so. 

Hi,

From the waveform you can see that the SW has some voltage ring when switching on/off, the 100nF capacitor will help to reduce this. And you can also add a snubber between SW and GND to reduce this voltage ring as well.

BR

Patrick

I think everything works fine now! 

Would you please give me some more info about the temperature values of the Evaluation board. Like the temperature of the inductor or Diode reached during some experiments or test, just need them for reference values? In my design on white background and full brightness the inductor body reaches 60 Degrees Celsius, at room temperature of 26 degrees.   

Hi,

Could you please share with me your inductor PN and do you have any waveform of inductor current?

BR

Patrick

Hello, 

The part number is: SRI1207-101MSRI1207-101M.pdf

Hi,

OK, so could you please also upload the inductor current waveform?

BR

Patrick