DS90UB953-Q1: Abnormal operation at low temperature - 40 ℃

Hi Hamzeh,

The customer feedback:

The DES used now is 960, synchronous mode. There is no problem at normal temperature. When it is low temperature, the linklock is disconnected and cannot be started. 

Is the temperature protection mechanism of this register ( ALARM_SENSE_EN (Address 0x1D)，T_UNDER R/W 0x0 Enable Temp Sensor under the low limit alarm) causing this problem, but we don't know how to configure these related registers to solve our current problem.

Hello Amy,

are you enabling the Temp sensor alarm? If yes, which registers are you writing?

If no, then how do you know this register is causing the problem?

Can you send a register dump from SER and from DES in a good mode and in error mode?

I don't know whether this temperature protection mechanism will lead to the disconnection of Ser and des links. At the same time, I won't configure the temperature alarm mechanism. At present, the relevant registers in this part are configured by default.

So what I want to know is whether the temperature alarm mechanism of 953 will disconnect Ser and des link? How should the temperature alarm mechanism be configured correctly? If I want to turn off this temperature alarm mechanism, how should I configure the register?

Hello Amy,

the integrated in the SER is just Temp sensor, not a Temp protection mechanism. If this is correctly programmed for a certain Temp limit, it will just rise a flag once that limit is hit. The SER or DES will not do anything else. They also will not disconnect the link or lose LOCK.

Is it possible that the low-temperature disconnection problem is related to the change of the ripple of the 953 power supply in the low-temperature environment? Because we can't measure the ripple of the power supply in the low-temperature environment, we can only evaluate it with the normal temperature data. The ripple requirement of the 953 data sheet for the power supply is 25mV p-p. must this ripple requirement be met? If the power ripple is too large, will the link of SerDes be disconnected?

Hello Amy,

you need to make sure that all specs of the Device are met all all temperatures, not only room temp.

I have asked you in my first reply if you can send a register dump from SER and from DES in a good mode and in error mode?

Hi Hamzeh,

The customer feedback:

1. This is the register value at - 30 ℃. At this time, the link is still linked, but if it cools down again, the link will be disconnected immediately.

2. This is the register value of 25 ℃ at normal temperature.

3. The link has been disconnected at - 40 ℃, and the register value of 953 cannot be dumped.

I read some TI materials and mentioned that power supply noise, impedance continuity of FPDLINK  line and frequency offset may affect the link stability of FPDLINK. The power supply ripple is about 20mV under normal temperature, which is already very low. Due to the limitation of the environment, we can't measure it at low temperature. Moreover, generally, the performance of this power chip will be reduced at high temperature, and the possibility that the performance will be reduced at low temperature is not mentioned.

The routing of FPDLINK on PCB is the inner layer, with an impedance of 50 Ω. The upper and lower layers are complete strata, which should be no problem.

Regards，

Amy

Another problem with this customer：

FDP link has an AEQ that can compensate for the change of FDP link line insertion loss. How should we configure these related registers.

Hello Amy,

Can you please provide the dumps in text form, so that I can search and copy?

Is it not possible to dump the 953 locally?

Also,what do you have in the climate champer, the SER only or both devices?

Hello Hamzeh,

The customer feedback:

This part of the register file will be re exported in text format and uploaded.

Our product definition is that the I2C of 953 is only pulled up, and the configuration of 953 can only be configured through 960 after 960 lock.

There is only ser-953 in the climate chamber. Des-960 is placed outside at room temperature.

At present, we have also done some experiments, using TI's 960 corresponding tools to test the Link margin of SER at different temperatures. The Link margin at room temperature and high temperature is very good, which is basically the best performance. When it is below - 10 ℃, the Link margin will slowly deteriorate, EQ / SP will fail, and there are more and more red branches. Wait until - 40  ℃ and the lock is completely disconnected.

Regards，

Amy

Hello Amy,

it is clear that if the signal quality is bad then MAP results will be worst until all red.

Please provide as I said, the dumps in text form, so that I can search and copy.

Hi Hamzeh,

I'm very sorry, this customer has raised a lot of questions:

We have tested and found that using Non-Synchronous mode is more stable at low temperature, so we have several questions about Non-Synchronous:

1、Whether Synchronous mode and Non-Synchronous do have different requirements for peripheral circuits, especially the requirements of S11 and S12. Is Synchronous mode more stringent.

2、Which of the two modes of Non-Synchronous external clock and Non-Synchronous internal Clock is more stable? It is better to keep the transmission stable after the change of external factors (such as S11 and S12). What is the reason?

In addition to the difference of voltage dividing resistance on the Mode pin, whether the two Non-Synchronous modes need to change the settings of registers related to 953 and 960？

3、What is the difference between 25M and 50M in the selection of crystal oscillator for Non-Synchronous external clock? Are the configurations different on 953 and 960?

4、Can Non-Synchronous only run 2G? Must the AC capacitor here strictly choose 100nF + 47nF? Is the choice of AC capacitance determined by mode or rate?

5、If we choose the Non-Synchronous mode, but we choose the combination of 33nF + 15nF for AC capacitance, is it OK? What are the risks?

6、If our current hardware mode and software configuration work in synchronous mode, but the external clock IC input by CLKIN pin of 953 is SMD, will this affect the operation of synchronous mode

7、 If the Mode pin of 953 is configured as Non-Synchronous external clock mode, but the configuration of 960 is Synchronous mode, can it work normally and what are the risks？

Hi Hamzeh,

Thank you very much for your reply. Another question from the customer, please help reply.

Now it works in the Non-Synchronous   external clock（50M)  mode. When testing the link margin, it is found that the Linked here is 100MHz by default. What does the Linked frequency represent? Why does the input of 50MHz become 100MHz? At this time, when testing the link margin, the two lines will fail and the lock will be disconnected. After Digital Reset, the linked is normal.

If CLKIN_DIV=2, the Linked clock here will become 50MHz, and the test link margin can be tested normally. What is the reason for this

Hi Hamzeh,

The problem we're having is that if use the 953 default FPD3_PLCK=100M, the test of the linked with TI tools is stable, but once click Linkmargin to test the Link , it disconnects. Margin couldn't test either, and the linked was OK after clicking Digital Reset again. However, with FPD3_PLCK=100M, our product works and the graphics are all fine.

Linkmargin could be tested if FPD3_PLCK=50M and margin was good, but the FPD3_PLCK=50M did not meet our image transmission bandwidth requirements.

So I want to know if the FPD3_PCLK=100M is something that needs to be set up to test Linkmargin properly, after all, at this time our product is working properly, and we can't just test Linkmargin.

Our operating mode is Non-Synchronous External Clock and the external crystal is 50M.

Hello Amy,

please do not relay on just doing the MAP Tool test to verify your link. This Tool result is an instant snap shot from a single system. If you want to test your system and qualify it you should use the VNA and measure the Return Loss and Insertion Loss over the complete used frequency range on different systems and make sure this fulfills our Channel specifications!