L5963 datasheet(37/49 Pages) STMICROELECTRONICS

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L5963

Thermal design

The PCB design should take into account also thermal aspects.

The maximum power manageable by the IC depends on how the board is designed and on

the package junction to ambient thermal resistance.

The temperature inside the IC (junction temperature) should not exceed 150 °C or one or

more thermal shut-down protections intervene.

The total power dissipation is approximately given by the sum of the power dissipation of the

two dc-dc regulators and the linear regulator:

Pd = Pdpwm1 + Pdpwm2 + Pdldo

Where:

PdissDC/DC = IloadDC/DC x VoutDC/DC x (1-)/;

 is the efficiency, as shown in Figure 7 and 8.

PdissLDO = IloadLDO x (VINLDO-VOUTLDO)

The junction temperature is estimated in this way:

Tj = Ta + Pd x Rthj-a

Where:

Ta is the maximum ambient temperature;

Rthj-amb is the junction to ambient thermal resistance, as defined in Table 5 and Table 6.

The slug has to be connected to the ground plane, whenever possible.

According to below formula and considering TSD_TH thermal shutdown minimum threshold

at 150 °C, maximum suggested power dissipation, for a slug-down configuration, can be

easily retrieved:

PDISS_suggested = (TSHD - Tamb) / Rthj-a

Table 9. Maximum suggested power for L5963 in PSSO36 slug-down package

Symbol

Tamb 105 °C

Tamb 80 °C

Rth j-a-2s

0.85 W

1.32 W

Rth j-a-2s2p

1.66 W

2.6 W

Rth j-a-2s2pvias

2.05 W

3.2 W

Table 10. Maximum suggested power for L5963 in QFN48 package

Symbol

Tamb 105 °C

Tamb 80 °C

Rth j-a-2s

0.68 W

1.06 W

Rth j-a-2s2p

1.41 W

1.19 W

Rth j-a-2s2pvias

1.73 W

2.7 W

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