ST1S40IPUR datasheet(17/30 Pages) STMICROELECTRONICS

17 / 30 page

ST1S40

Application information

Doc ID 17928 Rev 4

17/30

6.4

Thermal dissipation

The thermal design is important in order to prevent thermal shutdown of the device if

junction temperature goes above 150 °C. The three different sources of losses within the

device are:

conduction losses due to the ON resistance of high side switch (RHS) and low side

switch (RLS); these are equal to:

Equation 22

where D is the duty cycle of the application. Note that the duty cycle is theoretically given by

the ratio between VOUT and VIN, but is actually slightly higher to compensate the losses of

the regulator.

switching losses due to high side Power MOSFET turn ON and OFF; these can be

calculated as:

Equation 23

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 7. 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 24

Table 8.

Output capacitors

Manufacturer

Series

Cap value (

μF)

Rated voltage (V)

ESR (m

Ω)

MURATA

GRM32

22 to 100

6.3 to 25

< 5

GRM31

10 to 47

6.3 to 25

< 5

PANASONIC

ECJ

10 to 22

6.3

< 5

EEFCD

10 to 68

6.3

15 to 55

SANYO

TPA/B/C

100 to 470

4 to 16

40 to 80

TDK

C3225

22 to 100

6.3

< 5

COND

OUT

–

()

⋅⋅

OUT

RISE

FALL

()

------------------------------------------- Fsw

⋅⋅

⋅

OUT

⋅⋅

⋅

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