• Crappy CDIL datasheet

    From Piotr Wyderski@21:1/5 to All on Sun Mar 27 09:59:47 2022
    Here is an interesting part for my application, especially because its
    very low C_in:

    https://www.tme.eu/Document/901eddfa360c5ef73460d5ceeadb1a22/CDD20N03.pdf

    But I have no clue how to parse this datasheet. On one hand, they say
    the maximum V_GS is 12V, which is OK and suggest a logic-level device.
    On the other, most of the specs are at V_GS=10V, which is scary if 12V
    is the abs. max. Figure 9 at page 4, the R_DS(V_GS) seems to come from
    another part, as they claim the fraction of a milliohm range. At the
    first page they claim R_DS_ON < 35mOhm@10V. It looks like a random
    collection of pages.

    Could someone more experienced with this type of "documentation" tell me
    what R_DS_ON can I expect at V_GS=5V?

    Best regards, Piotr

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  • From Anthony William Sloman@21:1/5 to Piotr Wyderski on Sun Mar 27 03:57:13 2022
    On Sunday, March 27, 2022 at 7:00:07 PM UTC+11, Piotr Wyderski wrote:
    Here is an interesting part for my application, especially because its
    very low C_in:

    https://www.tme.eu/Document/901eddfa360c5ef73460d5ceeadb1a22/CDD20N03.pdf

    But I have no clue how to parse this datasheet. On one hand, they say
    the maximum V_GS is 12V, which is OK and suggest a logic-level device.
    On the other, most of the specs are at V_GS=10V, which is scary if 12V
    is the abs. max.

    12V Gate-to-source is the the voltage they guarantee that the part will survive. As John Larkin points out from time to time, testing where the gate breaks down would destroy the part, so they don't do it, and you can probably get away with applying
    more volts to most parts.

    Figure 9 at page 4, the R_DS(V_GS) seems to come from
    another part, as they claim the fraction of a milliohm range. At the
    first page they claim R_DS_ON < 35mOhm@10V. It looks like a random collection of pages.

    The number on the vertical axis are probably actually in ohm, but some clown apparently decided to label them as milliohms.

    Could someone more experienced with this type of "documentation" tell me what R_DS_ON can I expect at V_GS=5V?

    At low current, perhaps 0.08 ohm. It seems to get up to 0.24 ohm at 9A, but note Fig 5, where the drain current hits a limit of about 7A at VGS=4V.

    It is spelled out in Figure 6, plotted as a function of drain current for both 4.5V gate-to-source and 10V .

    --
    Bill Sloman, Sydney

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to bombald@protonmail.com on Sun Mar 27 08:14:13 2022
    On Sun, 27 Mar 2022 09:59:47 +0200, Piotr Wyderski
    <bombald@protonmail.com> wrote:

    Here is an interesting part for my application, especially because its
    very low C_in:

    https://www.tme.eu/Document/901eddfa360c5ef73460d5ceeadb1a22/CDD20N03.pdf

    But I have no clue how to parse this datasheet. On one hand, they say
    the maximum V_GS is 12V, which is OK and suggest a logic-level device.

    Actually, it doesn't. It's a fairly high threshold part.

    On the other, most of the specs are at V_GS=10V, which is scary if 12V
    is the abs. max.

    10v is not scary, and parts are not supposed to fail at abs max. To
    get real performance, parts sometimes need to be run at abs max, or
    beyond. Abs max specs are often ultra conservative; I test parts to
    failure and back off some.

    Mosfet gates typically fail around 60 volts or so. There could be
    long-term degradation a bit below that.

    Buy a few and test them!

    Figure 9 at page 4, the R_DS(V_GS) seems to come from
    another part, as they claim the fraction of a milliohm range. At the
    first page they claim R_DS_ON < 35mOhm@10V. It looks like a random
    collection of pages.

    The initial slopes of fig 5 indicate typical Ron.
    Fig 9 looks about right if the units are ohms, not mohms.


    Could someone more experienced with this type of "documentation" tell me
    what R_DS_ON can I expect at V_GS=5V?

    Best regards, Piotr

    The state of data sheets in the semi business is a disgrace. They must
    assign the dullest, least numerate interns to composing data sheets,
    and seem to never correct even gross errors.

    Someone could do a fun web site pointing out bad data sheets, and
    buggy parts.

    RF part data sheets are invariably bad.





    --

    I yam what I yam - Popeye

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  • From Piotr Wyderski@21:1/5 to jlarkin@highlandsniptechnology.com on Sun Mar 27 18:14:51 2022
    jlarkin@highlandsniptechnology.com wrote:

    Actually, it doesn't. It's a fairly high threshold part.

    This is true, but then who in their right mind specifies 12V max and
    expects it to be driven at 10?

    10v is not scary, and parts are not supposed to fail at abs max.

    If the design is supposed to stay within the abs max, it leaves you only
    2V of margin for ringing. Regular FETs specify +/-20V for 10V operation.

    To get real performance, parts sometimes need to be run at abs max, or beyond. Abs max specs are often ultra conservative; I test parts to
    failure and back off some.

    Indeed, but in the first place the part must be inherently capable of
    some "real performance". This is a boring 30V FET. Its two advantages
    are low Ciss and super-low price. I need many and the 8mA available from
    a 74HCT595's output would still allow substantially sub-microsecond
    switching speeds, tremendously simplifying the module.

    Buy a few and test them!

    Not sure if it is the right approach. The next reel might have different
    specs. Nah, I think I will pay 2x its price to get a part with reliable
    specs. The AOD454, for instance.

    The initial slopes of fig 5 indicate typical Ron.
    Fig 9 looks about right if the units are ohms, not mohms.

    This was my initial assumption, but then the chart says sort of 80mOhms
    at 10V, while the first page says "RDS(ON) <35mΩ @ VGS=10V". This is 2x off.

    Best regards, Piotr

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to bombald@protonmail.com on Sun Mar 27 10:15:27 2022
    On Sun, 27 Mar 2022 18:14:51 +0200, Piotr Wyderski
    <bombald@protonmail.com> wrote:

    jlarkin@highlandsniptechnology.com wrote:

    Actually, it doesn't. It's a fairly high threshold part.

    This is true, but then who in their right mind specifies 12V max and
    expects it to be driven at 10?

    What's wrong with that? Seems perfectly sensible to me. 10 is less
    than 12.


    10v is not scary, and parts are not supposed to fail at abs max.

    If the design is supposed to stay within the abs max, it leaves you only
    2V of margin for ringing. Regular FETs specify +/-20V for 10V operation.

    To get real performance, parts sometimes need to be run at abs max, or
    beyond. Abs max specs are often ultra conservative; I test parts to
    failure and back off some.

    Indeed, but in the first place the part must be inherently capable of
    some "real performance". This is a boring 30V FET. Its two advantages
    are low Ciss and super-low price. I need many and the 8mA available from
    a 74HCT595's output would still allow substantially sub-microsecond
    switching speeds, tremendously simplifying the module.

    An HCT595 is rated 7 volts abs max. Nowhere near 12.

    And it will source a lot more than 8 mA, even if you only use one
    section.


    Buy a few and test them!

    Not sure if it is the right approach. The next reel might have different >specs. Nah, I think I will pay 2x its price to get a part with reliable >specs. The AOD454, for instance.

    The initial slopes of fig 5 indicate typical Ron.
    Fig 9 looks about right if the units are ohms, not mohms.

    This was my initial assumption, but then the chart says sort of 80mOhms
    at 10V, while the first page says "RDS(ON) <35m? @ VGS=10V". This is 2x off.

    Best regards, Piotr

    Better buy something else.



    --

    I yam what I yam - Popeye

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to bombald@protonmail.com on Sun Mar 27 10:29:49 2022
    On Sun, 27 Mar 2022 09:59:47 +0200, Piotr Wyderski
    <bombald@protonmail.com> wrote:

    Here is an interesting part for my application, especially because its
    very low C_in:

    https://www.tme.eu/Document/901eddfa360c5ef73460d5ceeadb1a22/CDD20N03.pdf

    But I have no clue how to parse this datasheet. On one hand, they say
    the maximum V_GS is 12V, which is OK and suggest a logic-level device.
    On the other, most of the specs are at V_GS=10V, which is scary if 12V
    is the abs. max. Figure 9 at page 4, the R_DS(V_GS) seems to come from >another part, as they claim the fraction of a milliohm range. At the
    first page they claim R_DS_ON < 35mOhm@10V. It looks like a random
    collection of pages.

    Could someone more experienced with this type of "documentation" tell me
    what R_DS_ON can I expect at V_GS=5V?

    Best regards, Piotr

    Take a look at TPIC6595.



    --

    I yam what I yam - Popeye

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  • From Piotr Wyderski@21:1/5 to jlarkin@highlandsniptechnology.com on Sun Mar 27 20:35:31 2022
    jlarkin@highlandsniptechnology.com wrote:

    Take a look at TPIC6595.

    I absolutely love this part, or, to be specific, its Nexperia's sister
    due to better specs. I am pulsing the -OE at 1MHz rate and drive 8
    flyback transformers directly from the chip. But it is open-drain, there
    is no HV push-pull version as far as I know. The FET drivers would be
    more complex than they need to be. Hence the 595 to close the gap: the
    same digital interface, 7V-capable and push-pull. The 70mA total is a
    bit low, but there are low Qg FETs and then the FET driver turns out to
    be a 560 Ohm gate resistor. Cheap and reliable.

    Best regards, Piotr

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  • From Piotr Wyderski@21:1/5 to jlarkin@highlandsniptechnology.com on Sun Mar 27 20:26:29 2022
    jlarkin@highlandsniptechnology.com wrote:

    What's wrong with that? Seems perfectly sensible to me. 10 is less
    than 12.

    If driven gently -- nothing wrong. Pumping a lot of current abruptly
    will cause overshoots, though. 20% safety margin is far less than the
    typical 100%. I wouldn't consider the part in a 10V system for this
    reason alone. However, this is a 5V system, so the margin is still huge,
    even at 12V. No issue here. But the specs don't make sense at this V_GS,
    so I will better keep away from this part.

    An HCT595 is rated 7 volts abs max. Nowhere near 12.

    The resistance in the 5-7V range is unknown. Even at the rated 10V you
    get contradicting numbers, depending on what chart/page you like more.

    And it will source a lot more than 8 mA, even if you only use one
    section.

    70mA total abs max and I want to use all the channels. That makes it
    8*8=64mA + some margin. Still, a microsecond is good enough.

    Better buy something else.

    Yes, the AOD454 looks decent and the datasheet is not
    self-contradictory. Above all, it is fully specified at 4.5V.

    Best regards, Piotr

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  • From jlarkin@highlandsniptechnology.com@21:1/5 to bombald@protonmail.com on Sun Mar 27 11:36:05 2022
    On Sun, 27 Mar 2022 20:26:29 +0200, Piotr Wyderski
    <bombald@protonmail.com> wrote:

    jlarkin@highlandsniptechnology.com wrote:

    What's wrong with that? Seems perfectly sensible to me. 10 is less
    than 12.

    If driven gently -- nothing wrong. Pumping a lot of current abruptly
    will cause overshoots, though. 20% safety margin is far less than the
    typical 100%. I wouldn't consider the part in a 10V system for this
    reason alone. However, this is a 5V system, so the margin is still huge,
    even at 12V. No issue here. But the specs don't make sense at this V_GS,
    so I will better keep away from this part.

    An HCT595 is rated 7 volts abs max. Nowhere near 12.

    The resistance in the 5-7V range is unknown.

    The HCT output resistance? Measure it. These parts are not specified
    as mosfet gate drivers, so if you want to use them, experiment.

    Even at the rated 10V you
    get contradicting numbers, depending on what chart/page you like more.

    The data sheet curves for the fet are pretty complete. Derate a bit
    maybe for part variations. Again, measure to confirm.


    And it will source a lot more than 8 mA, even if you only use one
    section.

    70mA total abs max and I want to use all the channels. That makes it
    8*8=64mA + some margin. Still, a microsecond is good enough.

    Charging and discharging some mosfet gates won't overheat an HCT part.
    Or cause electromigration.


    Better buy something else.

    Yes, the AOD454 looks decent and the datasheet is not
    self-contradictory. Above all, it is fully specified at 4.5V.

    Best regards, Piotr


    --

    I yam what I yam - Popeye

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  • From Anthony William Sloman@21:1/5 to Piotr Wyderski on Sun Mar 27 21:11:27 2022
    On Monday, March 28, 2022 at 3:15:09 AM UTC+11, Piotr Wyderski wrote:
    jla...@highlandsniptechnology.com wrote:

    <snip>

    Fig 9 looks about right if the units are ohms, not mohms.

    This was my initial assumption, but then the chart says sort of 80mOhms
    at 10V, while the first page says "RDS(ON) <35mΩ @ VGS=10V". This is 2x off.

    Figure 9 is at a drain current of 3A. Figure 6 shows a significant rise in drain resistance with increasing drain current.

    Figures are mostly typical values. The first page number is talking about the worst cast drain resistance. They are different. Three-to-one differences between best case and worst case numbers aren't unusual.

    --
    Bill Sloman, Sydney

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