TS4997 datasheet(25/34 Pages) STMICROELECTRONICS

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TS4997

Application information

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Tamb is calculated as follows:

Equation 7

Therefore, the maximum allowable value for Tamb is:

Tamb = 150 - 85 x 2 x 1.266=42.4°C

If a 4-layer PCB with vias is used, RTHJAQFN16 = 45°C/W and the maximum allowable

value for Tamb in this case is:

Tamb = 150 - 45 x 2 x 1.266 = 93°C

4.8

Footprint recommendation

Footprint soldering pad dimensions are given in Figure 72 on page 31. As discussed in the

previous section, the maximum allowable value for ambient temperature is dependent on

the thermal resistance junction to ambient RTHJA. Decreasing the RTHJA value causes better

power dissipation.

Based on best thermal performance, it is recommended to use 4-layer PCBs with vias to

effectively remove heat from the device. It is also recommended to use vias for 2-layer PCBs

to connect the package exposed pad to heatsink cooper areas placed on another layer.

For proper thermal conductivity, the vias must be plated through and solder-filled. Typical

thermal vias have the following dimensions: 1.2mm pitch, 0.3mm diameter.

Figure 65.

QFN16 footprint recommendation

4.9

Decoupling of the circuit

Two capacitors are needed to correctly bypass the TS4997: a power supply bypass

capacitor CS and a bias voltage bypass capacitor Cb.

amb

150

° CR

TJHA

TotalP

dissmax

–

TS4997 데이터시트(PDF) 25 Page - STMicroelectronics