Cirrus Logic CS35L00 - Manual (Page 32)

CS35L00
32 DS906PP1
8.4.1 Determining Maximum Ambient Temperature
To determine (to a first order approximation) the maximum ambient temperature in which the CS35L00
will operate, the following equations can be used:
Where:
T
max
= The maximum ambient temperature in which the device can operate.
T
op
= The operating temperature of the device, given a dissipated power “P
max”
and a known thermal
impedance “ θ
JA
”.
T
TE
= The Over-Temperature Error Threshold, given in the “Characteristics & Specifications” section on
page 8 .
θ
JA
= The thermal impedance of the device and PCB. (This value is highly subjective to a number of ap-
plication specific scenarios. The numbers given in Table 2 on page 31 can be used for a first order ap-
proximation, but proper characterization of the application’s specific PCB and supporting mechanicals is
needed to increase the accuracy of the result achieved here.)
P
max
= The maximum power at which the amplifier will be operated continuously. (For conservative esti-
mates, the 10% THD+N rated power given in “Characteristics & Specifications” section on page 8 can be
used. However, this method will predict higher operating temperatures than what may be seen in the ap-
plication, since power content of audio signals is much smaller than that of the sine wave used to establish
the power specifications.)
η = The efficiency of the device at the power P
max
. (A safe, conservative assumption is 85%)
T
op
θ
JA
1
η
–
( ) P ×
max
( ) ×
=
T
max
T
TE
T
op
– =