iMX8MQ SOC_0V9 and DRAM_1V0 higher current

[NathanSmith]

I have an iMX8MQ board, based on the EVK, that has been in production.  After about 400 units we started seeing a higher number of iMX8’s drawing more current on the DRAM_1V0 and SOC_0V9 rails.  The board fab lot did change but we see no differences in the artwork.  I used the serial boot mode used for DRAM training to ensure I’m using the same configuration for the measurements and the same target DRAM configuration file.  The extra current typically amounts to about 60mA to 80mA (or more) on SOC_0V9 and 20mA on DRAM_1V0.  The ARM_0V9 is also slightly higher on these iMX8s.  The issue is that this causes higher thermal load that exceed the thermal management solution causing a shutdown at 95C.  We did find a lot of poor layout with the DRAM interface that we rectified, but I can’t help but wonder how this could also affect the SOC_0V9. 

Our power supply board is separate, so I used the same power supply board for the comparisons.  Voltages are all compliant in both configurations of a ‘good’ and a ‘bad’ board.

‘Good board’ using the DDR calibration tool

DRAM_1V0  On -24mA, Download config-168mA , After Calibrate 344mA

SOC_0V9 On-488mA, Download config-496mA, After calibrate 496mA

‘Bad board’ (results vary)

DRAM_1V0  On -44mA, Download config-184mA , After Calibrate 372mA (extra 20 mA)

SOC_0V9 On-544mA, Download config-572mA, After calibrate 576mA

I did find that the PCIe, USB2 and HDMI peripherals are powered although the interfaces are not used.  I don’t think the serial boot loader is trying to do anything with those peripherals.

I was expecting this to be a good ‘baseline mode’ for the iMX8 but I can’t really figure out what is causing this beyond the DRAM layout issues.  I’ve been through the Hardware Developers guide multiple times and can’t seem to find anything we have missed.

When the serial boot loader mode is active or application / mission mode is active, what can cause differences in the SOC_0V9 current consumption when the board / software is the same?  I would like some advice from someone knowledgeable before spinning a board.

[NathanSmith]

Will there be an updated version of AN12118 that will include maximum currents for these test cases? 

Is there some guidance beyond that given for the iMX8QMax on how much higher the Q currents will be for each iMX8M power net? 

It is very hard to design a thermal management solution for a small mobile package when I don't know how high these currents will get. 

Is there an app note on the part markings?  We see the die code and date code but we don't know what SBBG and SBAR are representing.

[igorpadykov]

max. currents also are described in Table 10. Maximum supply currents 

i.MX 8M Dual / 8M QuadLite / 8M Quad Applications Processors Data Sheet for Consumer Products

Info about part marking and future app note updates can be obtained through local marketing office.

Best regards
igor

[NathanSmith]

Thanks for the documents.  It looks like the iMX8QMax document is brand new.  This is rather frightening as we are already into production with this device and our thermal management solution is no longer able to handle the variation we are seeing from the parts.  I'm not used to devices demonstrating such a wide range of current consumption under even the most modest test cases.  We must have been lucky for the units so far. 

Is there any date code / lot information that can help sort out devices that may exhibit the poor power efficiencies for the iMX8MQ parts?

[igorpadykov]

>Is there any date code / lot information that can help sort out devices

>that may exhibit the poor power efficiencies for the iMX8MQ parts?

sorry such date code / lot information is not available.

Best regards
igor

[igorpadykov]

Hi Nathan

such differencies can be due to factory die process variation as described for

example in histograms provided in sect.B.2. Die process variation AN5215

i.MX 6 Temperature Sensor Module - Application Note

and currents data described in AN13249

i.MX 8QuadMax Current Drain with Low- and High-Power Use Cases

i.MX8MQ can have similar differences in current consumption.

Best regards
igor