DP83848C: DP83848C

Hi Xiang,

I am not understanding the question. You said the boards works normally. Is there any problem or you just are looking for a schematic review?

Thanks,

David

dear David,

1. Customer complaints
The customer complained that the LAN could not be connected in March, 23. Defective products complaints about 40PCS. The production date is from May to September 2021. The defective IC mark is 09C1EVT.

1.1) Defective IC is heated at 350°C, and then the LAN defect disappears at -20°C~70°C. Why is that?
1.2) The production of 3000PCS of equipment has been completed, can it be sold?

2. Line optimization
During the analysis, the above three points are different from the recommended routes.
Change it to the new line, please help confirm whether it is correct?

Thanks,

Xiang

Hi Xiang,

So 40 out of 3000 boards are non-functional, is my understanding correct? Has the problem been narrowed down to the PHY itself? If so, how? Does an A-B-A swap of the IC fix the issue?

Defective IC is heated at 350°C, and then the LAN defect disappears at -20°C~70°C.

Why is the device being heated to 350C? This is extremely hot and far outside the absolute maximum rating of the part. This would explain why the parts are non functional. 

I will have a look at the schematic and get back to you next week.

Thanks,

David

dear David,

During repair, use hot air at 350°C to take the IC.

A-B-A switches IC, and the defect disappears.

Thanks,

Xiang

Hi Xiang,

Is it possible the absolute max ratings are being violated during soldering? This could explain the failure if the die temperature is reaching more than 121.5C or the lead temperature is more than 260C for more than 10 seconds.

Thanks,

David

dear David,

1. In RMII mode, MCU connects to RX-DV, but not CRS-DV.

The data manual uses CRS-DV. Is there any problem using RX_DV here? What's the difference with CRS_DV?

2. Install 4.7KΩ 1% resistance with RBIAS. What's the problem?
(The data manual requires 4.87KΩ1%)

3. PFBOUT, PFBIN1 and PFBIN2 are connected to DC3.3V power supply. What's the problem?
(Data manual requirements, not connected to the power supply).

Thanks,

Xiang

Hi Xiang,

1. The RMII specification requires CRS-DV. It is a muxing of the signals Carrier Sense/Receive Data Valid.

2. Datasheet requires 4.87kΩ +- 1%. Functionality cannot be guaranteed outside the datasheet requirements. 

3. This is the requirement for power feedback connection. The second schematic which you have shared is correct. The first is incorrect.

Thanks,

David

dear David

I'm very sorry, I need you to confirm again.

TXD_2,TXD_3 Add a pull-down resistor of 2.2KΩ, is it necessary?

What should I do with idle IO?

Thanks,

Xiang

Hi Xiang,

It is fine to terminate unused input pins, yes. Unused output pins should be left floating.

Thanks,

David