Datasheet

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Low-EMI Switch
THERMAL INFORMATION
P
D(MAX)

T
J(MAX)
 T
A
R
JA

150°C  85°C
38.1 kW
 1700 mW
TPS61090
TPS61091, TPS61092
SLVS484A – JUNE 2003 – REVISED APRIL 2004
The device integrates a circuit that removes the ringing that typically appears on the SW node when the
converter enters discontinuous current mode. In this case, the current through the inductor ramps to zero and the
rectifying PMOS switch is turned off to prevent a reverse current flowing from the output capacitors back to the
battery. Due to the remaining energy that is stored in parasitic components of the semiconductor and the
inductor, a ringing on the SW pin is induced. The integrated antiringing switch clamps this voltage to VBAT and
therefore dampens ringing.
Implementation of integrated circuits in low-profile and fine-pitch surface-mount packages typically requires
special attention to power dissipation. Many system-dependent issues such as thermal coupling, airflow, added
heat sinks and convection surfaces, and the presence of other heat-generating components affect the
power-dissipation limits of a given component.
Three basic approaches for enhancing thermal performance are listed below.
• Improving the power dissipation capability of the PCB design
• Improving the thermal coupling of the component to the PCB
• Introducing airflow in the system
The maximum junction temperature (T
J
) of the TPS6109x devices is 150°C. The thermal resistance of the 16-pin
QFN PowerPAD package (RSA) isR
ΘJA
= 38.1 °C/W, if the PowerPAD is soldered and the board layout is
optimized. Specified regulator operation is assured to a maximum ambient temperature T
A
of 85°C. Therefore,
the maximum power dissipation is about 1700 mW. More power can be dissipated if the maximum ambient
temperature of the application is lower.
If designing for a lower junction temperature of 125°C, which is recommended, maximum heat dissipation is
lower. Using the above equation (8) results in 1050 mW power dissipation.
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