DCP021205：Bench TEST results

Hi Kenji,

Are the output voltage measurements at the output pins? Is the layout following the layout guidelines outlined in the datasheet? Improper probing technique can cause misrepresentation of output voltage regulation and improper PCB layout can cause additional losses seen in load regulation.  

I don't think this was asked in the previous thread, can you provide the schematic and PCB layout? Figure 6-16  is what was actually tested on an EVM and recently added into the datasheet to help customers get a rough understanding of the load regulation for for this device. 

Your bench test results look valid as they are close/within range of the device comparison table in the datasheet.

Regards,

Jimmy 

Hi jimmy-san,

Thank you for your answer.

It was a bench test of the IC, so I measured it with a simple circuit.

For voltage measurement, the pin closest to the IC was measured with a digital multimeter.

Insert Cin(2.2uF), Cout(1.0uF) as shown in Figure 8-1 of the data sheet, apply 12V with a regulated power supply, and apply current to the load side by an electronic load to reduce the voltage near the IC.

The voltage value of 300mA has to enter 4.75V~5.25V, one of the results is 5.35V. I understand this is out of scope.

Is this a measurement error due to the barracks, or is there another factor?

It's a reconfirmation just in case, but do you understand that you are doing 100% inspection with ATE?

Best Regards,

Kenji

Hi Kenji,

How many units do you see with output voltage regulations above the maximum? 

Can you give a waveform scopeshot of VIN, VOUT, and IOUT? Have you also tried using a power resistive load to see if the results are similar? Perhaps you can retest the simple circuit with a 16.6ohm resistor and recheck output voltage regulation.

The eload has some internal capacitance and I wonder if that is interacting with the unregulated module and slightly pulling the output voltage up above the max expected output voltage at 75% loading.

Regards,

Jimmy 

Hi Jimmy-san,

Thank you for your advice.

Unfortunately the waveform is not taken.

Also, because of COVID19, I'm currently teleworking, so I can't immediately see it in the lab.

2pcs were measured and 1pcs was out of the measuring range.

Attach the test results.

I would appreciate any advice.

DCP021205：TEST results.pdf

Best Regards,

Kenji

Hi Kenji-san,

I got back information from the team that the devices do go through full load testing. I quote "they are all 100% tested including Vout +/5% at 300mA and also fully loaded to 400mA for a load reg check".

It's hard to say right now what the issue is since you only have 2 sample size. I would suggest when you get a chance to go into the lab and retest with a power resistor pulling 300mA and recheck the load regulation. As stated previously I've had issues with eloads that slightly pull the output voltage up because of the internal capacitance before.Perhaps when you get a chance to use the lab, you can test a few more samples (if you have any) and get a rough idea of the expected load regulation for these devices. 

Again, Figure 6-16 load regulation at 5V output is an actual EVM test that was recently done on a DCP021205 device. This graph is what a typical DCP021205 output voltage would look like but there will be +/- 5% variation from part to part. In your case the variation for "#1 device" is closer to 7%. Will this cause an issue in your application? 

I think your measurements are valid, though I'd suggest retesting with power resistors to reconfirm as stated previously.

Regards,

Jimmy

Hi Jimmy-san,

We did the bench test again in the lab.

The wiring length has been shortened using a universal board.

Then, the load was measured in three patterns.

16.7Ω resistive load/electronic load (CC mode: 300mA)/electronic load (CR mode; 16.7Ω)

Below are the results.

① 16.7Ω resistance resistance

　　Ref1: 5.603V　Ref2: 4.975V

② Electronic load (CC mode: 300mA)

　　Ref1: 5.649V　Ref2: 4.956V

③ Electronic load (CR mode; 16.7Ω)

　　Ref1: 5.613V　Ref2: 4.973V

As you say, compared to the 16.7Ω resistor, the electronic load has a slightly higher voltage, but this time again it was out of the 5V ± 5% range.

I would like some advice on the results of Ref1

Best Regards,

Kenji

Hi Kenji,

It sounds like simply shortening the wire length brought the output voltage regulation from both devices (Ref1 and Ref2). Assuming that the shortened setup is the same for when you tested Ref1 and Ref2 it's interesting to see that Ref1 device had a larger output voltage shift.

Notice that your original output voltage measurement at 300mA E-load was 5.354V (Ref1) and 4.806V(Ref2). Now the output voltage with the shortened setup with 300mA E-load is 5.649V (Ref1) and 4.956V (Ref2).

Do you have the layout for the "simple circuit and universal board" used to test these two devices? Is Ref1 and Ref2 on the same board with the same layout? 

Again I'd like to mention that based on your description of the schematic "Insert Cin(2.2uF), Cout(1.0uF) as shown in Figure 8-1 of the data sheet, apply 12V with a regulated power supply", it sounds like you are using the typical recommended schematic in the datasheet. 

Do you have any additional samples that you can test to get a broader sample of the output voltage regulation using these parts on your simple circuit board? 

Can you also provide the date code for these devices? I'm thinking of using this information to check with the internal team on data test logs on device lots. 

Regards,

Jimmy