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:

a)

Equation 22

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

the regulator.

b)

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

calculated as:

Equation 23

equivalent switching time is 20 ns.

c)

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

P

COND

R

HS

I

OUT

2

DR

LS

I

OUT

2

1D

–

()

⋅⋅

+

⋅⋅

=

P

SW

V

IN

I

OUT

T

RISE

T

FALL

+

()

2

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

⋅⋅

⋅

V

IN

I

OUT

T

SW

F

SW

⋅⋅

⋅

==

P

Q

V

IN

I

Q

⋅

=