8.2.2.13 Power Dissipation Estimate

The following formulas show how to estimate the TPS54560B power dissipation under CCM operation. Do not use these equations if the device is operating in DCM.

The power dissipation of the IC includes conduction loss (P_COND), switching loss (P_SW), gate-drive loss (P_GD), and supply current (P_Q). Example calculations are shown with the 12-V typical input voltage of the design example.

Equation 52.

spacer

Equation 53.

spacer

Equation 54.

spacer

Equation 55.

where

• I_OUT is the output current (A).
• R_DS(on) is the on-resistance of the high-side MOSFET (Ω)
• V_OUT is the output voltage (V).
• V_IN is the input voltage (V).
• fsw is the switching frequency (Hz)
• trise is the SW pin voltage rise time and can be estimated by trise = V_IN x 0.16 ns/V + 3 ns
• Q_G is the total gate charge of the internal MOSFET
• I_Q is the operating nonswitching supply current

Therefore,

Equation 56.

For given T_A,

Equation 57.

For given T_JMAX = 150°C

Equation 58.

where

• Ptot is the total device power dissipation (W)
• T_A is the ambient temperature (°C).
• T_J is the junction temperature (°C).
• R_TH is the thermal resistance of the package (°C/W)
• T_JMAX is maximum junction temperature (°C)
• T_AMAX is maximum ambient temperature (°C).

There will be additional power losses in the regulator circuit due to the inductor ac and dc losses, the catch diode and PCB trace resistance impacting the overall efficiency of the regulator.