Datasheet

ADP5065 Data Sheet
Rev. D | Page 36 of 40
JUNCTION TEMPERATURE
In cases where the ambient temperature, T
A
, is known, the
thermal resistance parameter, θ
JA
, can be used to estimate the
junction temperature rise. T
J
is calculated from T
A
and P
D
using
the formula
T
J
= T
A
+ (P
D
× θ
JA
) (9)
The typical θ
JA
value for the 20-bump WLCSP is 46.8°C/W (see
Table 5). A very important factor to consider is that θ
JA
is based
on a 4-layer, 4 in × 3 in, 2.5 oz copper board as per JEDEC
standard, and real applications may use different sizes and
layers. It is important to maximize the copper to remove the heat
from the device. Copper exposed to air dissipates heat better
than copper used in the inner layers.
When designing an application for a particular ambient
temperature range, calculate the expected ADP5065 power
dissipation (P
D
). From this power calculation, the junction
temperature, T
J
, can be estimated using Equation 9.
Maximum junction temperature (T
J
) can also be calculated
from the board temperature (T
B
) and power dissipation (P
D
)
using the formula
T
J
= T
A
+ (P
D
× θ
JB
) (10)
where θ
JB
is the junction-to-board thermal resistance.
The typical value for the 20-bump WLCSP is 9.2°C/W (see
Table 5). θ
JB
is based on a 4-layer, 4 in × 3 in, 2.5 oz copper
board, as per the JEDEC standard.
For a WLCSP device, where possible, remove heat from every
current carrying bump (PGNDx, VINx, SWx, ISO_Sx, and
ISO_Bx). For example, thermal vias to the board power planes
can be placed close to these pins, where available.
The reliable operation of the charger can be achieved only if the
estimated die junction temperature of the ADP5065 (Equation 9)
is less than 125°C. Reliability and mean time between failures
(MTBF) are highly affected by increasing the junction temper-
ature. Additional information about product reliability is
available in the ADI Reliability Handbook at the following URL:
www.analog.com/reliability_handbook.