BD3509MUV-E2 データシートの表示（PDF） - ROHM Semiconductor

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BD3509MUV-E2

Nch FET Ultra LDO for PC Chipsets with Power Good

ROHM Semiconductor 

BD3508MUV,BD3509MUV

Technical Note

●Heat Loss

Thermal design should allow operation within the following conditions. Note that the temperatures listed are the allowed

temperature limits, and thermal design should allow sufficient margin from the limits.

1. Ambient temperature Ta can be no higher than 100 ℃.

2. Chip junction temperature (Tj) can be no higher than 150℃.

Chip junction temperature can be determined as follows:

① Calculation based on ambient temperature (Ta)

＜Reference values＞

Tj=Ta+θj-a×W

θj-a: VQFN020V4040 367.6℃/W Bare (unmounted) IC

178.6℃/W 4-layer substrate (bottom layer surface copper foil area 10.29mm2)

103.3℃/W 4-layer substrate (bottom layer surface copper foil area 10.29mm2)

35.1℃/W 4-layer substrate (top layer copper foil area 5505mm2)

Substrate size: 74.2×74.2×1.6mm3 (substrate with thermal via)

It is recommended to layout the VIA for heat radiation in the GND pattern of reverse (of IC) when there is the GND pattern in

the inner layer (in using multiplayer substrate). This package is so small (size: 4.2mm×4.2mm) that it is not available to

layout the VIA in the bottom of IC. Spreading the pattern and being increased the number of VIA like the figure below).

enable to get the superior heat radiation characteristic. (This figure is the image. It is recommended that the VIA size and the

number is designed suitable for the actual situation.).

Most of the heat loss that occurs in the BD3509MUV is generated from the output Nch FET. Power loss is determined by the

total VIN-Vo voltage and output current. Be sure to confirm the system input and output voltage and the output current

conditions in relation to the heat dissipation characteristics of the VIN and Vo in the design. Bearing in mind that heat

dissipation may vary substantially depending on the substrate employed (due to the power package incorporated in the

BD3509MUV) make certain to factor conditions such as substrate size into the thermal design.

Power consumption (W) = Input voltage (VIN)- output voltage (Vo) ×Io (Ave)

Example) VIN=1.5V, Vo=1.25V, Io(Ave) = 4A

Power consumption (W) = 1.5(V)-1.2(V) ×4.0(A)

= 1.0(W)

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2010.04 - Rev.C

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