Hi there,
I'm using TPS561208 in my circuit. Vin=5V and I want to get 3.3V at output pin. I designed the schematic as same as Webench circuit. But I'm getting 3.6V constantly.
Webench circuit:
My circuit:
I dont understand what is the problem. I tried to use the same products selected in Webench and the same schematic as Webench.
Hi Edwin,
I measured with osciilloscope like you want. B (the blue one) is input, C (the black one) is output, A (the red one) is SW pin.
And you can see webench analysis as below.
Startup:
Load Transient:
Input Transient
Steady State:
Hi Edwin,
There is only TPS561208 on the board. There is no case of any other IC affecting the TPS561208.
You can see the VFB voltage on the oscilloscope as follows.
Hi Edwin,
I tried it using 2 pcs PCBs but it doesnt correctly. Then in case there is a problem with the PCB,I soldered it to the perforated pertinax. I still haven't been able to get an accurate result.
The time/div value in the previous image was larger, I saw that when I zoomed in. You can see my zoomed output signal as below.
I couldnt measure in one picture, because 1 probe is broken on oscilloscope but I measured same time/div all of these.
Red = Vin
Blue =Vout
Green = Feedback
And the last one is SW
Hi Holly,
Sorry for my delay. Green's name is D. In picture, it seems like black.
Hi Holly,
I did not connect a load outside. I'm aiming to only see 3.3V. I'll add it to my circuit after I see it. At first it was feeding my microcontroller, but when the 3.3V line was not correct, I removed all the remaining components to test the DC/DC converter.
Yellow is SW, Blue is Vout.
I hope this pictures help you for solve the problem. When I measured Vout with multimeter, I read 3.6-3.7V.
Hi，
below is the waveform from datasheet. when Vfb is higher than voltage reference, SW become low, then inductor discharging.
according your test, your Vfb is always higher than the voltage reference. but your SW waveform have the off time. so, i confused.
maybe you have improper test.
