Hi,
please give us YOUR schematic.
Klaus
Hi,
But I don´t like the MOSFET selection.
Klaus
Hi,
in your schematic of post#3 there is a GND connection missing. PGND to AGND.
Klaus
Hi,
for sure you need to connect ALL GNDs.
Klaus
Hi,
The datasheet is your friend:
********
8.2.2.10 Output Voltage Divider
RFB1 and RFB2 set the output voltage level, the ratio of these resistors is calculated from:
R_FB2/R_FB1 = (V_OUT / 1.215V) - 1 (24)
RFB1 is typically 1.21 kΩ for a divider current of 1 mA. The divider current can be reduced to 100 μA with
RFB1=12.1 kΩ. For the 5V output design example used here, RFB1 = 1.21 kΩ and RFB2 = 3.74 kΩ.
********
Klaus
Hi,
R_FB1 and R_FB2 set the output voltage.
All other changes are for proper operation of the regulator.
(Imagine R_FB1 and R_FB2 act like a steering wheel of a car. But to keep track you additionally need to adjust your car speed to the road surface.)
-->
* A percentual change in R_FBx results in an percentual change in V_OUT
But:
* A percentual change in L will not change output voltage
* A percentual change in Rt will not change output voltage
* A percentual change in CRamp will not change output voltage
Klaus
Hi,
I'm guessing
* PCB layout problem (we can't review, because you didn't give this picture)
* part selection. Especially all Ls, Cs and Ds. A single value (like 22uH) is not enough. We need the datasheets to be able to review them.
Klaus
Hi,
No GND plane?... those thin wires for low impedance connections?...No wonder i doesn´t work.
Didn´t you read the datasheet? ... and the layout guidelines?
Klaus
When you look at the layout example of the datasheet you see that there are actually no "wires" but completely filled areas.I read the datasheet and followed it
Added:And please post your PCB layout BEFORE you produce the PCB.
We will help you to get good results.
Also still missing: a detailed description of your parts. As said 22uH is not enough information to validate an inductance.
Klaus
Hi,
When you look at the layout example of the datasheet you see that there are actually no "wires" but completely filled areas.
And only some mm short.
You really need to keep on the guidelines. Design a new PCB.
Klaus
Hi,
the GND plane improves signal quality, but it also helps to distribute the heat.
--> single sided GND plane is sufficient. Via count improves low impedance and improves thermal conductivity.
Klaus
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