AN1882 datasheet(20/30 Pages) STMICROELECTRONICS

20 / 30 page

Thermal considerations

AN1882

20/30

Doc ID 10209 Rev 4

Thermal considerations

Depending on the electrical application conditions (input voltage, switching frequency, and

output current) and ambient temperature, the heat produced by device losses could

increases the junction temperature over its absolute maximum rating. The following relation

can estimate the junction temperature of the device:

Equation 22

where TA is the ambient temperature of the application, RTH_JA is the thermal resistance

junction to ambient of the package and PTOT is the overall power dissipated by the device.

RTH_JA depends a little bit on the application board but it can approximately considered

equal to 180 °C/W. PTOT is given by:

Equation 23

Figure 12.

Thermal performance results: VIN = 3.7 V VOUT = 1.8 V IOUT = 800 mA

Figure 13.

RDS(on) vs. temperature

For a better estimation of the power dissipated it can be useful to consider the MOSFETs

RDS(on) variation with the temperature, shown in the Figure 13.

THJA

TOT

⋅

TOT

MOS

SWIT CHING

GATECHARGE

AN1882 Datasheet(PDF) 20 Page - STMicroelectronics