ST1S32 datasheet(19/29 Pages) STMICROELECTRONICS

19 / 29 page

ST1S32

Application information

Doc ID 023246 Rev 1

19/29

Equation 24

where TRISE and TFALL are the overlap times of the voltage across the high-side power

switch (VDS) and the current flowing into it during turn-on and turn-off phases, as shown in

Figure 8. TSW is the equivalent switching time. For this device the typical value for the

equivalent switching time is 20 ns.

Quiescent current losses, calculated as:

Equation 25

where IQ is the quiescent current (IQ=1.2 mA maximum).

The junction temperature TJ can be calculated as:

Equation 26

where TA is the ambient temperature and PTOT is the sum of the power losses just seen.

RthJA is the equivalent thermal resistance junction-to-ambient of the device; it can be

calculated as the parallel of many paths of heat conduction from the junction to the ambient.

For this device the path through the exposed pad is the one conducting the largest amount

of heat. The RthJA measured on the demonstration board described in Section 5.5 is about

40 °C/W for the VFDFPN package.

OUT

RISE

FALL

()

-------------------------------------------

Fsw

⋅⋅

⋅

OUT

⋅⋅

⋅

Rth

TOT

⋅

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