L5963 datasheet(35/45 Pages) STMICROELECTRONICS

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L5963

Thermal design

The system design and maximum power that can be managed should take into account the

IC thermal resistance junction to ambient which depends on the PCB design.

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

more of the thermal shut-down protections will intervene.

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

two dc-dc regulators and the linear regulators:

Pd = Pdpwm1 + Pdpwm2 + Pdldo

Where:

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

 is the efficiency, as shown in Figure 6 and 7.

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 4: Thermal data

(slug-down configuration).

L5963 comes in two different package options, slug-up and slug-down, to meet power

management requirements and give flexibility in different board configurations (see

Section 9: Package information). 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 8. Maximum suggested power

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

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