10.3 Power Dissipation Estimate
The following formulas show how to estimate the IC power dissipation under continuous conduction mode (CCM) operation. The power dissipation of the IC (Ptot) includes conduction loss (Pcon), dead time loss (Pd), switching loss (Psw), gate drive loss (Pgd), and supply current loss (Pq).
Equation 42. Pcon = Io
2 × R
DS_on_Temp
where
- IO is the output current (A).
- RDS_on_Temp is the ON-resistance of the high-side MOSFET with given temperature (Ω).
Equation 43. Pd = ƒ
sw × Io × 0.7 × 40 × 10
–9
where
- IO is the output current (A).
- ƒsw is the switching frequency (Hz).
Equation 44. Psw = 1/2 × V
in × Io × ƒ
sw× 13 × 10
–9
where
- IO is the output current (A).
- Vin is the input voltage (V).
- ƒsw is the switching frequency (Hz).
Equation 45. Pgd = 2 × V
in × ƒ
sw× 10 × 10
–9
where
- Vin is the input voltage (V).
- ƒsw is the switching frequency (Hz).
Equation 46. Pq = V
in × 515 × 10
–6
where
- Vin is the input voltage (V).
So
Equation 47. Ptot = Pcon + Pd + Psw + Pgd + Pq
where
- Ptot is the total device power dissipation (W).
For given TA:
Equation 48. T
J = T
A + Rth × Ptot
where
- TA is the ambient temperature (°C).
- TJ is the junction temperature (°C).
- Rth is the thermal resistance of the package (°C/W).
For given TJmax = 150°C:
Equation 49. T
Amax = T
Jmax – Rth × Ptot
where
- Ptot is the total device power dissipation (W).
- Rth is the thermal resistance of the package (°C/W).
- TJmax is maximum junction temperature (°C).
- TAmax is maximum ambient temperature (°C).
There are additional power losses in the regulator circuit due to the inductor AC and DC losses and trace resistance that impact the overall efficiency of the regulator.