TPS61169: Spurious oscillation during TINA simulation

Hi Fred,

Could you provide inductor current waveform along with SW voltage waveform? It would be better if you zoom in these waveform so that we can see values clearly.

BTW, VOUT is 8.3V? Total output current is 135mA*8?

BR,

Robin

Hi,

Yes, 8.3V is VOUT, the voltage across the LEDs, but total current is about 135 mA. Each of the eight strings of three LEDs in series draws about 17 mA. Peak inductor current is 800 mA!:

Hi Fred,

It's abnormal and I need some time to check this. I will reply to you later. Besides, could you provide your simulation schematic?

BR,

Robin

Hi,

Here's the schematic:

OK!

Can I assume then, that an inductor value greater than the 10uH in the data sheet isn't problematic?

Hi Fred,

You need to calculate the average inductor current and ripple with 10uH to figure out that whether the circuit operates in CCM mode.

BR,

Robin

I stripped my simulation down to the absolute minimum, replaced all the passives except the diode with ideal components. I increased the output voltage to 17V, but the inductor current always goes to zero. What combination of input voltage, output voltage and current results in a steady duty cycle and non-zero inductor current from this part?

Hi Fred,

Average inductor current IL=VOUT*IOUT/VIN

Inductor current ripple Ir=VIN*Duty*Tsw/L

When IL>0.5*Ir, the device operates in CCM mode.

BR,

Robin

Hi Robin,

For my simulation, IL = 8.3V * 0.15A / 5V = 249mA.

Assuming Tsw is switching period, and inductance is most needed at 50% duty cycle, Ir = 5V * 50% * (1/1.2e6s) / 10e-6H = 208mA

So by a wide margin: IL > 0.5 * Ir. I should see CCM mode, but instead get this irregular duty cycle:

BTW, the SS parameter in the spice model appears to control soft start behaviour (SS=0 enables it). What's the DUTY parameter supposed to do?

Did you get my .TSC file?

Hi Fred,

I just got the file, but it cannot be opened. What's your software version?

BR,

Robin

Hi Robin,

I'm running TINA Version 12.1.30.114 BV-DS  (x64)

Tell me what version you're running and I'll send you a schematic in a compatible format.

Fred

Hi Fred,

Many thanks for your understanding! 

BR,

Robin

Hi Robin,

You're welcome.

What version of TINA are you running?

Fred

Hi Fred,

It seems you cannot view the picture uploaded yesterday.

"v9.3.200.277 SF-TI" version.