LS1027A custom board

[mkraj]

Hi

We have designed a new custom NXP LS1027A based board almost similar to LS1028A RDB.

While testing the new board , When we powered on, board is powering for some time and it is not working after Some time. Few impedences are becoming low(Before powering on all impedences are fine).

We have tested 4 cards and found below observations.

1. 2 cards initially powered on and stopped working after some time. We found few impedences are low after powering on.

2. Remaining 2 cards are drawing more currnet initially  and not powering on. Some of the impedences are became low. (We found processor is over heating )

Our board initial impedence are  as below

1V2	400
VTT_0V6	1.34k
MVREF	268k
5V0	59k
1V0	35.8
TA_BB_VDD	2.56k
12V0	129k *
1V35	4k
CPLD_1V8	391
2V5	360
EVDD	3.8k
1V8	376
3V3	270
VDD Core	20.2

Could you please suggest what could be the issue? Is there any chance of assembly problem?

With Regards

Krishnam Raju M

[June_Lu · Accepted solution]

For the general rule, you could check you power requirement of  power rail 3.3V. if the output current is larger than the theoretical requirement. And if your protection circuit is designed correctly, but damaged, there would be something wrong.

For the CPLD support, please kindly contact the vendor and the CPLD firmware designer.

Thanks

[mkraj]

Dear June_Lu
Thank you.

[June_Lu]

Incorrect voltage(VDD) maybe related to the design and assembly issue.

Please check if the design follow the AN12028_QorIQ LS1028A Design Checklist and LS1027A/LS1017A Data Sheet, especially the pins related to the issue power rail.

Assembly issue also should be exclusive.

Thanks

[mkraj]

Dear Lu 

Thank you for your reply.

1. In some cards , we found one more issue i.e 3.3V impedence is becoming low to 1.3 Ohm. Initially it was fine and around 500 Ohm. When we powered on it was drawing more current and our e-fuse getting damaged.After that when measured 3.3V impedence is very low(around 1.3 ohm). This voltage is going to CPLD , few processor pins and some ICs.

Is this 1.3 Ohm impedence because any IC might have damaged?

2. In some cards after programming CPLD(Before programming powers are stable), It is drawing more power and eFuse is getting damaged?

Thnak you

with regards

krishnam raju m

[mkraj]

Hi

Thank you for your reply.

We found one more issue, ie. core voltage VDD is dropping to .8V, when we are powering on the board.

What could be the issue.

With Regards

Krishnam Raju M

[June_Lu]

Impendences should be measured when power off.

If the board could not work, you could check the power rails and all signals which are related to the boot.

Assembly problem could not be exclusive.

For the issue boards, please check all power rails follow the SPEC, sequence, voltage, current, AN12028_QorIQ LS1028A Design Checklist, chapter 4 and Data Sheet, 3.1.

If the power rails are correct, please check related signals follow LS1028A Reference Manual 4.8.5 Power-On Reset Sequence Detailed Description.

For the overheating board, please confirm the heatsink design meet the requirement in the datasheet, chapter 5.

Thanks