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{
    "url": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/email/KVRZJCBBZW4NXI2TLVFVER3F44O5DYNV/",
    "mailinglist": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/",
    "message_id": "[email protected]",
    "message_id_hash": "KVRZJCBBZW4NXI2TLVFVER3F44O5DYNV",
    "thread": "https://mailman.amsat.org/hyperkitty/api/list/[email protected]/thread/KVRZJCBBZW4NXI2TLVFVER3F44O5DYNV/",
    "sender": {
        "address": "jbrandenburg (a) amsat.org",
        "mailman_id": "fba29bb05aa944e3b759fb437017d01e",
        "emails": "https://mailman.amsat.org/hyperkitty/api/sender/fba29bb05aa944e3b759fb437017d01e/emails/"
    },
    "sender_name": "Jonathan Brandenburg",
    "subject": "[pacsat-dev] Re: Latchup Protection and Watchdog Parts",
    "date": "2023-01-24T22:37:25Z",
    "parent": null,
    "children": [],
    "votes": {
        "likes": 0,
        "dislikes": 0,
        "status": "neutral"
    },
    "content": "On 1/19/23 17:40, Rich Gopstein via pacsat-dev wrote:\n> Burns might remember the details (or Zach certainly would), but one of \n> those parts was undersized for the RT-IHU and would cut out when we \n> were transmitting with the ax5043.  I think we had to back down the \n> xmit power in order for the device not to reset.\n>\n>\nIt didn't take a whole lot of research for me to figure this one out. \nThe FPF2001 used on the Fox boards has a fixed current limit of 50mA. I \ncan see that could be sufficient for the Fox IHU since it uses a low \npower processor and doesn't have transceivers or the power amplifier. \nThe direct replacement part for the FPF2001 is the TI TPS22942 and it \nappears to be pin compatible with a fixed limit of 100mA. Would a 100mA \nbe a problem on Fox? I wouldn't think it would cause failure in the 10ms \nit takes to blank the current but I make that statement without any real \nbasis. Perhaps the 40mA limit of the TI TPS22942 would be sufficient.\n\nAnyway, back to PACSAT...\n\nWith the higher current capacity of the MAX4995, adjustable between 0 \nand 600 mA, it could be the better choice than the fixed TI TPS22942. \nI'm not aware of flight experience with either so I tend to look to the \nMAX4995 with the adjustable and higher current limits. With this \ndecision and looking at the approach employed on the RT-IHU I could see \nthe following:\n\n1 - The TMS570 and associated circuitry get their own MAX4995. As a \nfirst order pass contained in Bob Stricklin's spreadsheet the current \nrequirement is 458.3mA, within the MAX4995's capabilities. If we want to \nfurther \"derate\" we could put the TMS570 on one MAX4995 and have a \nsecond MAX4995 for the peripherals.\n\n2 - All five AX5043's require 100mA. Would we want to have 2 of the \nAX5043's on one MAX4995 and the remaining AX5043's on the other MAX4995 \nin case one MAX4995 fails prematurely? The value of this would depend on \nall the AX5043's being equivalent in function (i.e., all could be used \nfor command and/or telemetry). This only takes care of this particular \nfailure mode and still leaves a lot of other failure modes in which an \nearly MAX4995 death would leave the system INOP so there may be limited \nvalue in using two MAX4995's for the AX5043's.\n\n3 - Finally, the amplifier/pre-amp is an additional 415mA. Again, if we \nwant to \"derate\" we could put the power amp on it's own MAX4995.\n\n\nIt looks like we need a minimum of 3 MAX4995's and a possible max of 6 \nMAX4995's. (With further analysis, we might need one more to split the \n1.2V and 3.3V power lines to the TMS570.) The MAX4995 are small chips so \ndon't require a lot of real estate. We can discuss the risk vs reward of \nusing more MAX4995's at some point.\n\nI welcome comments\n\nJonathan\n\n\n-- \nJonathan Brandenburg\nRadio Amateur Satellite Corporation\n1-214-213-1066\n\n",
    "attachments": []
}