JAJSLY1G July 2013 – June 2021 TPS54561
PRODUCTION DATA
The following formulas show how to estimate the TPS54561 power dissipation under continuous conduction mode (CCM) operation. These equations should not be used if the device is operating in discontinuous conduction mode (DCM).
The power dissipation of the IC includes conduction loss (PCOND), switching loss (PSW), gate drive loss (PGD) and supply current (PQ). Example calculations are shown with the 12-V typical input voltage of the design example.
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).
fsw is the switching frequency (Hz).
trise is the SW pin voltage rise time and can be estimated by trise = VIN x 0.16 ns/V + 3 ns
QG is the total gate charge of the internal MOSFET
IQ is the operating nonswitching supply current
Therefore,
For given TA,
For given TJMAX = 150°C
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 from junction to ambient for a given
PCB layout (°C/W).
TJMAX is maximum
junction temperature (°C).
TAMAX 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.