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 36. P
con = I
O2 × R
DS(on) (temperature dependent)
where
- IO is the output current (A)
- RDS(on) is the on-resistance of the high-side MOSFET with given temperature (Ω)
Equation 37. Pd = ƒ
sw × I
O × 0.7 × (20 nS + 20 nS)
where
- IO is the output current (A)
- ƒsw is the switching frequency (Hz)
Equation 38. P
sw = 0.5 × V
IN × I
O × ƒ
sw× 7 × 10
–9
where
- IO is the output current (A)
- VIN is the input voltage (V)
- ƒsw is the switching frequency (Hz)
Equation 39. P
gd = 2 × V
IN × ƒ
sw× 6 × 10
–9
where
- VIN is the input voltage (V)
- ƒsw is the switching frequency (Hz)
Equation 40. P
q = V
IN × 500 × 10
–6
where
- VIN is the input voltage (V)
So
Equation 41. P
tot = P
con + P
d + P
sw + P
gd + P
q
where
- Ptot is the total device power dissipation (W)
For given TA,
Equation 42. T
J = T
A + R
th × P
tot
where
- Ptot is the total device power dissipation (W)
- TA is the ambient temperature (°C)
- TJ is the junction temperature (°C)
- Rth is the thermal resistance of the package (°C/W)
For given TJ max = 150°C
Equation 43. T
A max = T
J max – R
th × P
tot
where
- Ptot is the total device power dissipation (W)
- Rth is the thermal resistance of the package (°C/W)
- TJ max is maximum junction temperature (°C)
- TA max 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.