ZHCSJU9E January 2007 – June 2019 TPS40077
PRODUCTION DATA.
The power dissipation in the TPS40077 is largely dependent on the MOSFET driver currents and the input voltage. The driver current is proportional to the total gate charge, Qg, of the external MOSFETs. Driver power (neglecting external gate resistance) can be calculated with Equation 5.
where
The total power dissipation in the TPS40077, assuming the same MOSFET is selected for both the high-side and synchronous rectifier, is described in Equation 6 or Equation 7.
or
where
The maximum power capability of the TPS40077 PowerPAD package is dependent on the layout as well as air flow. The thermal impedance from junction to air, assuming 2-oz. copper trace and thermal pad with solder and no air flow, is 37°C/W. See the application report titled PowerPAD Thermally Enhanced Package (SLMA002) for detailed information on PowerPAD package mounting and usage.
The maximum allowable package power dissipation is related to ambient temperature by Equation 8. For θJA, see Table 1.
THERMAL IMPEDANCE,
JUNCTION-TO-AMBIENT(1) |
TA = 25°C POWER RATING | TA = 85°C POWER RATING | |
---|---|---|---|
Natural convection | 37°C/W | 2.7 W | 1.08 W |
150 LFM airflow | 30°C/W | 3.33 W | 1.33 W |
250 LFM airflow | 28°C/W | 3.57 W | 1.42 W |
500 LFM airflow | 26°C/W | 3.84 W | 1.52 W |
Substituting Equation 8 into Equation 7 and solving for fSW yields the maximum operating frequency for the TPS40077. The result is described in Equation 9.