AN3994 datasheet(33/53 Pages) STMICROELECTRONICS

33 / 53 page

AN3994

MD II and MD V: which is the lowest loss one?

Doc ID 022380 Rev 1

33/53

Figure 42.

STP16N65M5 vs. STP18NM60N dv/dt at turn-off @ 3 A/6 A, 400 V

6.5

Comments about energy ON comparison

Considerations about energy comparison between the MD V and the MD II depend on the

gate resistor selected by the user.

As for turn-on energy, the bigger sizes of the MD V list considered in this work

(STP42N65M5 and STP35N65M5) perform worse than their equivalent MD II parts in the

entire RG range at the two current levels selected for the tests. This is due to the negative

gate charge impact (the Q12+Q23 portion, as explained in Section 4) together with the

higher threshold and plateau value of these parts if compared to the MD II devices.

Smaller sizes show a slightly different dynamic behavior: MD V parts (STP21N65M5 and

STP16 N65M5) perform worse than their equivalent MD II parts at relative medium/high RG

values (i.e. RG>10 Ω for the STP21N65M5, and RG>22 Ω for the STP16N65M5). This

situation changes if low RG values are used. Under the latter driving condition, the MD V

performs better than the MD II but, it is not advised to adopt very low RG values in most

common situations due to the increased voltage/current slopes of these small devices and

the consequent increased risk of spurious oscillations.

Anyway, if an MD V part (belonging to the list in Table 1) is used in any circuit with a specific

RGon value, and it needs to be replaced with an equivalent MD II part by keeping the same

Eon energy, this can be easily obtained by increasing its RGon value according to the charts

showing the Eon comparison reported in this work. The same way of proceeding can be

adopted if an MD V device must be used instead of an MD II equivalent part.

6.6

Comments about energy OFF comparison

As for turn-off, all MD V devices show better performances than their equivalent MD II parts.

Some exceptions arise for the smaller sizes (STP21N65M5 and STP16N65M5) when

current levels are significantly lower than the nominal current (see Figure 34 and 40).

The slightly worse MD V energy at very low current levels is linked to the behavior of the

MOSFET intrinsic capacitances. Output capacitance is charged up to VCLAMP during

AN3994 Datasheet(PDF) 33 Page - STMicroelectronics