TPS65286_15 Datasheet, PDF (34/46 Pages) Texas Instruments – TPS65286 Dual Power Distribution Switches With 4.5-V to 28-V Input Voltage, 6-A Output Current Synchronous Buck Regulator

TPS65286
SLVSCG1 – MARCH 2014
www.ti.com
10 Power Supply Recommendations
The total power dissipation inside TPS65286 should not to exceed the maximum allowable junction temperature
of 125°C. The maximum allowable power dissipation is a function of the thermal resistance of the package (θ_JA)
and ambient temperature. The analysis below gives an approximation in calculating junction temperature based
on the power dissipation in the package. However, it is important to note that thermal analysis is strongly
dependent on additional system level factors. Such factors include air flow, board layout, copper thickness and
surface area, and proximity to other devices dissipating power. Good thermal design practice must include all
system level factors in addition to individual component analysis.
To calculate the temperature inside the device under continuous load, use the following procedure.
1. Define the total continuous current through buck converter (including the load current through power
switches). Make sure the continuous current does not exceed maximum load current requirement.
2. From the graphs below, determine the expected losses (Y axis) in watts for buck converter inside the device.
The loss P_{D_BUCK} depends on the input supply and the selected switching frequency.
3. Determine the load current I_OUT1 and I_OUT2 through the power switches. Read R_DS(on)1/2 of power switch from
the typical characteristics graph.
4. The power loss through power switches can be calculated by P_{D_PW} = R_DS1(on) × I_OUT1 + R_DS2(on) × I_OUT2.
5. The Dissipating Rating Table provides the thermal resistance θ_JA for specific packages and board layouts.
6. To calculate the maximum temperature inside the IC, use the following formula.
T_J = (P_{D_BUCK} + P_{D_PW} ) × θ_JA + T_A
where
• T_A = Ambient temperature (°C)
• θ_JA = Thermal resistance (°C/W)
• P_{D_BUCK} = Total power dissipation in buck converter (W)
• P_{D_PW} = Total power dissipation in power switches (W)
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