The following formulas show how to estimate the
device power dissipation under continuous-conduction mode (CCM) operations. These
formulas must not be used if the device is working in the discontinuous-conduction
mode (DCM) or pulse-skipping Eco-mode.
The device power dissipation includes:
- Conduction loss:
Pcon =
IOUT2 × RDS(on) × VOUT /
VIN
where
- IOUT is the
output current (A).
- RDS(on) is the
on-resistance of the high-side MOSFET (Ω).
- VOUT is the
output voltage (V).
- VIN is the
input voltage (V).
- Switching loss:
Psw = 0.5 × 10-9 ×
VIN2 × IOUT ×
ƒSW
where
- ƒSW is the
switching frequency (Hz).
- Gate charge loss:
Pgc = 22.8 × 10-9
× ƒSW
- Quiescent current loss
Pq = 0.11 × 10-3 ×
VIN
Therefore:
Ptot = Pcon + Psw + Pgc + Pq
where
- Ptot is the total device power dissipation
(W).
For given TA :
TJ = TA + Rth × Ptot
where
- TJ is the junction temperature
(°C).
- TA is the ambient temperature
(°C).
- Rth is the thermal resistance of the package
(°C/W).
For given TJMAX = 150°C:
TAMAX = TJMAX – Rth × Ptot
where
- TJMAX is maximum junction temperature
(°C).
- TAMAX is maximum ambient temperature
(°C).