PCA9624 All information provided in this document is subject to legal disclaimers. © NXP Semiconductors N.V. 2016. All rights reserved.
Product data sheet Rev. 4.1 — 18 January 2016 21 of 40
NXP Semiconductors
PCA9624
8-bit Fm+ I
2
C-bus 100 mA 40 V LED driver
10.1 Junction temperature calculation
A device junction temperature can be calculated when the ambient temperature or the
case temperature is known.
When the ambient temperature is known, the junction temperature is calculated using
Equation 4
and the ambient temperature, junction to ambient thermal resistance and
power dissipation.
(4)
where:
T
j
= junction temperature
T
amb
= ambient temperature
R
th(j-a)
= junction to ambient thermal resistance
P
tot
= (device) total power dissipation
When the case temperature is known, the junction temperature is calculated using
Equation 5
and the case temperature, junction to case thermal resistance and power
dissipation.
(5)
where:
T
j
= junction temperature
T
case
= case temperature
R
th(j-c)
= junction to case thermal resistance
P
tot
= (device) total power dissipation
Here are two examples regarding how to calculate the junction temperature using junction
to case and junction to ambient thermal resistance. In the first example (Section 10.1.1
),
given the operating condition and the junction to ambient thermal resistance, the junction
temperature of PCA9624PW, in the TSSOP24 package, is calculated for a system
operating condition in 50 C
1
ambient temperature. In the second example
(Section 10.1.2
), based on a specific customer application requirement where only the
case temperature is known, applying the junction to case thermal resistance equation, the
junction temperature of the PCA9624PW, in the TSSOP24 package, is calculated.
1. 50 C is a typical temperature inside an enclosed system. The designers should feel free, as needed, to perform their own
calculation using the examples.
T
j
T
amb
R
th j-a
P
tot
+=
T
j
T
case
R
th j-c
P
tot
+=
