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I'm going though datasheets of some dual N-channel MOSFETs for li-ion battery protection, like 8205A or ECH8695R, for some thermal and power dissipation calculations.

There are Rds(on) values, like 13.3 mΩ @ 2.5 V (in ECH8695R) or 0.040 Ω @ Vgs=2.5V (in 8205A).
Is this value just for one MOSFET in the package or for both of them (when they are wired in series as they should be)?
It would be huge difference whether it is just for one MOSFET or for whole package, but I do not see any mention of that in the datasheets.

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3 Answers 3

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You can safely assume that the listed values are per transistor, there simply happen to be two transistors in one package but that should be seen as something unrelated.

If the numbers were for two MOSFETs in parallel that would be explicitly stated as the connections of the MOSFETs are separate so they can be used independently.

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  • \$\begingroup\$ Those MOSFETs are supposed to be wired in series, not parallel. They are for battery protection, pretty standard arrangement. \$\endgroup\$
    – Chupacabras
    Commented Jun 4, 2019 at 9:52
  • \$\begingroup\$ Why should I safely assume that the listed values are per transistor? For power dissipation maybe. But it influences overcurrent protection as well, because it is based on Rdson values. \$\endgroup\$
    – Chupacabras
    Commented Jun 4, 2019 at 9:55
  • \$\begingroup\$ They are for battery protection That might be how you use them. Only in the datasheet of the ECH8695R is it clear that this is designed for battery protection. But still, the parameters are for individual MOSFETs. \$\endgroup\$
    – Bimpelrekkie
    Commented Jun 4, 2019 at 9:56
  • \$\begingroup\$ Why should I safely assume that the listed values are per transistor? Because it is "common practice", if a manufacturer deviates from that they would explicitly state that. However measuring and specifying a (more complex) 2 MOSFET circuit is more complex than specifying and measuring a single MOSFET device. Another reason: Rdson is lower for one device than 2 devices in series. Manufacturers want a low Rdson on the datasheet because that looks better. \$\endgroup\$
    – Bimpelrekkie
    Commented Jun 4, 2019 at 9:59
  • \$\begingroup\$ It's confusing. ECH8695R specifies max. allowed power dissipation 1.5W (for whole package). And allows max. 11A drain current. That would mean resistance of 12.4 mΩ which is pretty close to those stated Rdson values. It would mean that Rdson is for whole package for both MOSFETs in series. Did I make some mistake in my calculation? \$\endgroup\$
    – Chupacabras
    Commented Jun 4, 2019 at 10:03
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All the static and dynamic parameters are given per unit since this type of chips contain identical units.

For the chips that you are asking about, the Rds value is given for each MOSFET. Because they are not connected in parallel and not have to be even if they are in common-drain configuration.

EDIT: The junction temperature is a limiting factor here. Since max junction temperature is 150°C, max allowed temp rise, for 24°C amb, is 126°C. Given Rth from junction to amb is 89°C/W, max allowed power dissipation is 1.41W. If only one MOSFET is driven and the drain current is 11A then Rds will be ~11.7mR which is pretty close to the datasheet values.

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  • \$\begingroup\$ It's confusing. ECH8695R specifies max. allowed power dissipation 1.5W (for whole package). And allows max. 11A drain current. That would mean resistance of 12.4 mΩ which is pretty close to those stated Rdson values. It would mean that Rdson is for whole package for both MOSFETs in series. Did I make some mistake in my calculation? \$\endgroup\$
    – Chupacabras
    Commented Jun 4, 2019 at 10:05
  • \$\begingroup\$ This actually approves that the values are given for a single MOSFET but the package (IOW, the junction trmperature) is a limiting factor. Think about this: If you drive one MOSFET only and the drain current is 11A then the junction temperature will reach the max allowed value, 150°C. Because the Rth from junction to amb is 89°C/W hence max allowed temp rise is (for 24°C amb) is 126/89 = ~1.41W thus Rds = 1410/121 = 11.7mR - pretty close to the datasheet values. \$\endgroup\$
    – Rohat Kılıç
    Commented Jun 4, 2019 at 10:41
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I have contacted ON Semiconductor support about ECH8695R.
Their response is:

The ECH8695R has specified RDSon 13.3mOhm @ 2.5 V. This measurement symbol is RDSon so it is for single MOSFET in that package

So I assume this applies for other devices as well.

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