Heatsink


The thermal characteristics of any IC are determined by four parameters. Maximum allowable IC chip junction temperature TJ and thermal resistance Rθ are specified by the IC manufacturer. Ambient temperature TA and the power dissipation PD are determined by the:





For a MOSFET

PDISS - power dissipated by a MOSFET
IO - load current
RDSON - Dran to Source ON resistance of a MOSFET
DC - duty cycle. DC is 1 for continuous conduction.


PDISS = 1.6 I2O RDSON DC





Junction-to-ambient = Junction-to-case + case-to-ambient
Junction-to-board thermal resistance or Junction-to-ambient thermal resistance:




Result:




Thermal resistance Rθ is the basic thermal characteristic for ICs. It is usually expressed in terms of OC/W and represents the rise in junction temperature with a unit of power applied in still air. Total IC power to be dissipated depends on input current, output current, voltage drop, and duty cycle.
Required thermal resistivity of a heatsink (maximum):


Rθsa = ( TJ - Ta ) / PDISS - ( RθJC + RθCS )

Heatsink Surface Area

50 / √ A = Rθsa

AMIN = ( 50 / Rθsa )2

Enter:





Result: