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Crappy CDIL datasheet

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

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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

Reply to
Piotr Wyderski
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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.

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

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 .

Reply to
Anthony William Sloman

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

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

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

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.

Reply to
jlarkin

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

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.

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.

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.

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

Reply to
Piotr Wyderski

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

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.

Better buy something else.

Reply to
jlarkin

Take a look at TPIC6595.

Reply to
jlarkin

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.

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.

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.

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

Best regards, Piotr

Reply to
Piotr Wyderski

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

Reply to
Piotr Wyderski

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

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

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

Reply to
jlarkin
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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.

Reply to
Anthony William Sloman

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