I have DC/DC converter ADP2108AUJZ-1.5. This chip mast out 1.5V. Bat on PCB I see 1.0V! Load is resistor 1 kOhm or "no load". Chip has marking "LAA" - this marking for 1.5V. I check 3 chips - all outs 1.0V! Why?
What input voltage and current limit are you using? If the input side voltage is low or the current is limited, it might be causing the lowered output depending on the load.
Input voltage is 5V, no current limit (>10W). I took clear PCB and install only ADP2108AUJZ-1.5-R7 with CAPs 4.7uF, 10uF and IND 2.2uH (LQM2MPN2R2NG0). Instead load I install 1kOhm. Voltage on load is 1.0V! I tested 3 chips. May be marking “LAA” on this chips is wrong?
ADP2108AUJZ-3.3-R7 work good.
I am not sure why it would not work so first I want to make sure everything is connected correctly,
Have you tested the 3.3V version with the same circuit (LCs and in the same board location?)
Can you take a scope picture of the SW node?
What voltage do you see on pin 3 and 4?
Are you sure the FB sense line is actually connected to Vout?
With no load resistor what's the output voltage?
Thank You for suggestions!
I will try ADP2108AUJZ-3.3 instead (in place) ADP2108AUJZ-1.5 – it is possible!
I attached fragment of PCB for ADP2108AUJZ-1.5.
I will make scope on pin SW (pin 5) – I remember, that it was how “Figure 27 (“no load”)” from Data Sheet, but I will check.
Pin 4 is 1.0V with 1 kOhm and without load.
Pin 1, 3 is 5.1V.
I will check all pins once more.
I made scope on pin5 (SW) for ADP2108AUJZ-1.5 (marking LAA) - it is in attachment
Out=1V (mast be 1.5V)
It seems like you have a 1V version of the part insteadof the 1.5V version. I do not see anything wrong with your set-up.
A 1Kohm load is only 1mA, and as you can see from your scope plots you are running in power saving mode.
As a last test, increase the load to 5ohm (2.5ohm<R<10ohm) to see if it is still regulating at 1V with full load (it should).
If that is the case order some new samples of the 1.5V version, where did you buy those from?
This chips isn't "Analog Devices"!
Today I have learned that it have bought in China! Chineses warned that it can be a fake. If I knew it earlier, I wouldn't set questions!
But I made scope on pin5 (SW) for load 5 Ohm - it is in attachment. Output - 1V, frequency - 3MHz.
we always recommend you buy from authorized distributors to prevent such issues. Or you can always request samples or small orders on the ADI web site.
I see from your scope plots that there is a lot of ringing (oscillations) on your supply and GND. This is due to either probing technique or layout on the board.
I marked up your layout to show you how to improve the performance of the IC. It is important to keep the capacitors as close to the IC as possible and the GND connection between the IC and input and output caps as short and "wide" as possible.
The red arrows are component movements and vias removal, the yellow section is the proposed new location. I hope this helps.
Big thank You for replay and excuse me for delay!
It is very pleasantly Your attention.
Samples have long time of delivery – 4 weeks. Distributors or not have it or sell bobbins. Farnell not sell ADP2108AUJZ. China deliver for 1..2 weeks... I make devider on pin 4 and get 1.5V...
ADP2108AUJZ: SOT-23, 3MHz, 600mA – it is good! But very bad sell!
My scope is very noisy: it is sufficiently connect SIG and GND contacts on probe and touch GND plan and I get 100mV rms noise. Very big ring, may be, get scope…
Thank You for suggestion about layout.
I seek make a little two cycles: “CAP-in > SW-pin > Ind > CAP-Out” and “GND-pin > SW-pin > Ind > CAP-Out”. It is possible in my case make theirs more little, but I wanted simplify mounting.
I usually place vias under case for thermal sink. You have removed 2 vias – connection to GND mast be only in one point: near CAPs? SOT-23-5 has only one pin to GND (pin №2) and these 2 vias, probably, don’t have meaning for thermal sink...
Retrieving data ...