ST1S41 datasheet(18/27 Pages) STMICROELECTRONICS

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Application information

ST1S41

18/27

DocID023654 Rev 2

6.4

Thermal dissipation

The thermal design is important to prevent the 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 the high-side switch (RHS) and low-

side switch (RLS); these are equal to:

Equation 23

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 actually it is 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 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 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 25

where IQ is the quiescent current (IQ=2.5 mA maximum).

The junction temperature TJ can be calculated as:

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

Table 8. Output capacitors (continued)

Manufacturer

Series

Cap value (

μF)

Rated voltage (V)

ESR (m

Ω)

COND

OUT

–

()

⋅⋅

OUT

RISE

FALL

()

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

Fsw

⋅⋅

⋅

OUT

⋅⋅

⋅

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