ST1S31PUR datasheet(19/35 Pages) STMICROELECTRONICS

19 / 35 page

DocID022998 Rev 4

19/35

ST1S31

Application information

In Table 8 some capacitor series are listed.

5.4

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 high-side switch (RHS) and low-side

switch (RLS); these are equal to:

Equation 24

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 it is actually slightly higher to compensate the losses of

the regulator.

switching losses due to high-side power MOSFET turn-on and turn-off; these can

be calculated as:

Equation 25

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 the turn-on and turn-off phases, as shown

in Figure 9. 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 26

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

Table 8. Output capacitors

Manufacturer

Series

Cap value (

µF)

Rated voltage (V)

ESR (m

)

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

PCOND

RHS IOUT

2 DR

LS IOUT

–





PSW

VIN IOUT

TRISE TFALL



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





VIN IOUT TSW FSW





VIN IQ



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