TPS54335A: variable Uout

Hi,

Can you upload the full application circuit for better understanding? you may send email to us if there concern on IP.

my email add.: andy.chen@ti.com

yup...

i made the pictures with KiCAD and GIMP:

-arne

Hi
Your application is below, right?
Vin 24V
Vout 12V
LED Load 2A -max
Fsw=114KHz

How do you calculate the compensation network on COMP pin? the calculation procedure on data sheet is for voltage output, not for current source output.

You may try first to change C329 from 18pF to 1nF--4.7nF to see if any improvement.

Can you test PH node waveform when circuit unstable?

Hi!

Yes, u r right... but Vout is between 5V and 14V (for 4 blue LEDs in series; red/green/blue can use up to 1A; and white up to 2.4A...)...

I tried 2nF as C329 instead of 18pF, but it did not help... I think my feedback circuit causes the problem...

I changed the range of DAC3 now: it is between 1.2V and 2.4V... i think the opamp U312 does not like it, when its positive input is too close to 0V... in addition i had to decrease the amplification factor of U312 (R333 is 1.43kR now)...

now it works better

• up to 10V with a purely ohmic 10R load and
• up to 8V (3 red LEDs at 1A), BUT:
• that 12V white LED still flickers...

could a large R319 (in the COMP-pin circuit) help?

or is it more like my feedback circuit is not so good for higher Vout?

For the values  of R319, C330, C329 i used the C program in the appendix... I chose a value that was somewhere in the middle... *giggle*

-arne

appendix:

#include <math.h>
#include <stdio.h>
#include <stdlib.h>

int main(int argc, char ** argv) {
	if (argc!=3) return 1;
	double vmax = atof(argv[1]);
	double vstep = vmax/5;
	double imax = atof(argv[2]);
	double istep = imax/5;
	double co = 121e-6;
	double f = 114e3;
	double fc = f/10;
	double re = 5e-3;
	for (double v=vstep; v<=vmax; v+=vstep) {
		double r4 = 2*M_PI*fc*v*co / ((1300e-6)*8*.8);
		printf("v:%4.1fV r4:%4.1fkR",v,r4*1e-3);
		for (double i=istep; i<=imax; i+=istep) {
			double rl = v/i;
			double c4 = rl*co / r4;
			double c6 = re*co / r4;
			printf(" | %3.0fnF %3.0fpF",c4*1e9,c6*1e12);
		}
		printf("\n");
	}
	return 0;
}