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Differences between PicoZed 7Z030 REVC01 and REVC04

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I have a custom PicoZed carrier board. The PicoZeds that I have been using with it are labeled BD-Z7PZP-7Z030-G REVC01. These have been working. I just received a new batch of PicoZeds labeled BD-Z7PZP-7Z030-G REVC04.

When I plug these new pz boards into my carrier, set them to cascaded JTAG boot mode, and power them up, I get green power good lights on both the pz and my carrier. Then, after a second or so, I see the blue FPGA_DONE light on my carrier light up. At this point, I don't expect the FPGA to have been configured, as it is in JTAG mode. Furthermore, I can not see the device on the JTAG chain.

Are there any differences between the two revisions of the boards that may be causing this? I've already tried changing the position of JT2 to match the PUDC settings of REVC01. This had no effect. 

One more data point to confuse things: When I plug the new picozeds into my Avent FMC Carrier Card Rev C, the boards work as expected.

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    The problem is back. I opened up a couple more of the new picozeds and attempted to use them. Same issue - DONE light comes on when pl hasn't yet been configured and I can't see the device on JTAG.

    I followed a trail of fluctuating power sources and power source enables back to find that PWR_ENABLE was oscillating. Item 3.5 of the picozed errata shows that the newer boards have R52 removed because this was pulling up the enable pin of the TPS54618 to a voltage higher than the maximum. After placing a 10k resister in R52, the picozed REVC04 works like normal. 

    I have two main questions:

    Why do the picozeds without the PWR_ENABLE pull-up cause PWR_ENABLE to oscillate on my custom carrier board and not on the FMC Carrier? Control of PWR_ENABLE on my custom carrier is similar to that on the Avnet PicoZed FMC Carrier C03. The MOSFET is a BSS138LT1G (same as on FMC carrier), but the controlling voltage is +15V, R103 has been changed to 1k, C92 to 0.1uF, and R106 to 20k.


    Is the EN pull-up to 5V really detrimental to the TPS54618? I have been running picozeds with this pullup constantly for months now without any of them failing. Also, the details of the current pull-up within the regulator aren't clear to me. I suppose I want to know more information about the enable comparator in the TPS54618.

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    The problem is back. I opened up a couple more of the new picozeds and attempted to use them. Same issue - DONE light comes on when pl hasn't yet been configured and I can't see the device on JTAG.

    I followed a trail of fluctuating power sources and power source enables back to find that PWR_ENABLE was oscillating. Item 3.5 of the picozed errata shows that the newer boards have R52 removed because this was pulling up the enable pin of the TPS54618 to a voltage higher than the maximum. After placing a 10k resister in R52, the picozed REVC04 works like normal. 

    I have two main questions:

    Why do the picozeds without the PWR_ENABLE pull-up cause PWR_ENABLE to oscillate on my custom carrier board and not on the FMC Carrier? Control of PWR_ENABLE on my custom carrier is similar to that on the Avnet PicoZed FMC Carrier C03. The MOSFET is a BSS138LT1G (same as on FMC carrier), but the controlling voltage is +15V, R103 has been changed to 1k, C92 to 0.1uF, and R106 to 20k.


    Is the EN pull-up to 5V really detrimental to the TPS54618? I have been running picozeds with this pullup constantly for months now without any of them failing. Also, the details of the current pull-up within the regulator aren't clear to me. I suppose I want to know more information about the enable comparator in the TPS54618.

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