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TSZ02201-0J3J0AJ00110-1-2

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ROHM Co., Ltd. All rights reserved.

11/17

02.MAR.2012 Rev.001

TSZ22111･15･001

0J3J0AJ00110

Datasheet

Switching Regulator Efficiency

Efficiency ŋ may be expressed by the equation shown below:

Dissipation factors:

1) ON resistance dissipation of inductor and FET：PD(I

2) Gate charge/discharge dissipation：PD(Gate)

3) Switching dissipation：PD(SW)

4) ESR dissipation of capacitor：PD(ESR)

5) Operating current dissipation of IC：PD(IC)

1)PD(I

current.)

2)PD(Gate)=Cgs×f×V

(Cgs[F]：Gate capacitance of FET, f[H]：Switching frequency, V[V]：Gate driving voltage of FET)

Consideration on Permissible Dissipation and Heat Generation

As this IC functions with high efficiency without significant heat generation in most applications, no special consideration is

needed on permissible dissipation or heat generation.

In case of extreme conditions, however, including lower input

voltage, higher output voltage, heavier load, and/or higher temperature, the permissible dissipation and/or heat generation

must be carefully considered.

For dissipation, only conduction losses due to DC resistance of inductor and ON resistance of FET are considered.

Because the conduction losses are considered to play the leading role among other dissipation mentioned above including

gate charge/discharge dissipation and switching dissipation.

Fig.27 Thermal derating curve

(VCSP50L2)

=0.135+0.11

=0.245[Ω]

P=0.3

With the

consideration on the dissipation as above, thermal design must be carried out with sufficient margin allowed.

η=

Vin×Iin

×100[%]=

Pin

×100[%]=

α

×100[%]

Vin

3)PD(SW)=

Ambient temperature:Ta [℃]

0

25

50

75

100

125

150

0

1.0

0.66W

VCSP50L2(2.50×1.10mm□)

ROHM standard 1 layer board

Board size：50mm×58mm

θj-a=189.4℃/W

0.8

0.6

0.4

0.2