Data Sheet ADP194
Rev. A | Page 11 of 12
THERMAL CONSIDERATIONS
Power dissipation due to ground current is quite small and
can be ignored. Therefore, the junction temperature equation
simplifies to the following:
In most applications, the ADP194 does not dissipate much heat
due to its low on-channel resistance. However, in applications
with high ambient temperature and high load current, the heat
dissipated in the package can cause the junction temperature of
the die to exceed the maximum junction temperature of 125°C.
T
J
= T
A
+ {[(V
IN
− V
OUT
) × I
LOAD
] × θ
JA
} (3)
In cases where the board temperature is known, use the thermal
characterization parameter, Ψ
JB
, to estimate the junction temper-
ature rise. Maximum junction temperature (T
J
) is calculated
from the board temperature (T
B
) and power dissipation (P
D
)
using the formula
The junction temperature of the die is the sum of the ambient
temperature of the environment and the temperature rise of the
package due to the power dissipation, as shown in Equation 1.
T
J
= T
B
+ (P
D
× Ψ
JB
) (4)
To guarantee reliable operation, the junction temperature of
the ADP194 must not exceed 125°C. To ensure that the junction
temperature stays below this maximum value, the user must be
aware of the parameters that contribute to junction temperature
changes. These parameters include ambient temperature, power
dissipation in the device, and thermal resistances between the
junction and ambient air (θ
JA
). The θ
JA
value is dependent on
the package assembly compounds that are used and the amount
of copper used to solder the package GND pin to the PCB.
Table 5 shows typical θ
JA
values of the 4-ball WLCSP for various
PCB copper sizes. Table 6 shows the typical Ψ
JB
value of the
4-ball WLCSP.
PCB LAYOUT CONSIDERATIONS
The heat dissipation capability of the package can be improved
by increasing the amount of copper attached to the pins of the
ADP194. However, as listed in Table 5, a point of diminishing
returns is eventually reached, beyond which an increase in the
copper size does not yield significant heat dissipation benefits.
It is critical to keep the input and output traces as wide and as
short as possible to minimize the circuit board trace resistance.
Table 5. Typical θ
JA
Values for WLCSP
Copper Size (mm
2
) θ
JA
(°C/W)
0
1
260
50 159
100 157
300 153
500 151
1
Device soldered to minimum size pin traces.
Table 6. Typical Ψ
JB
Values
Package Ψ
JB
Unit
4-Ball WLCSP 58.4 °C/W
8629-025
The junction temperature of the ADP194 is calculated from the
following equation:
Figure 25. ADP194 PCB Layout
T
J
= T
A
+ (P
D
× θ
JA
) (1)
where:
T
A
is the ambient temperature.
P
D
is the power dissipation in the die, given by
P
D
= [(V
IN
− V
OUT
) × I
LOAD
] + (V
IN
× I
GND
) (2)
where:
I
LOAD
is the load current.
I
GND
is the ground current.
V
IN
and V
OUT
are the input and output voltages, respectively.
