cat4109 ON Semiconductor, cat4109 Datasheet - Page 8

• Manufacturer Part Number: cat4109
• Description: 3-channel Constant-current Rgb Led Driver With Individual Pwm Dimming
• Manufacturer: ON Semiconductor

CAT4109
APPLICATION INFORMATION
POWER DISSIPATION
The power dissipation (P
calculated as follows:
where V
the associated LED current. Combinations of high
V
the
applications where V
inserted in series with the LED string to lower P
Thermal dissipation of the junction heat consists
primarily of two paths in series. The first path is the
junction to the case (θ
defined by the package style, and the second path is
the case to ambient (θ
dependent on board layout. The overall junction to
ambient (θ
For a given package style and board layout, the
operating junction temperature T
power dissipation P
resulting in the following equation:
When mounted on a double-sided printed circuit
board with two square inches of copper allocated for
“heat spreading”, the resulting θ
For example, at 60°C ambient temperature, the
maximum power dissipation is calculated as follow:
Doc. No. MD-5042, Rev. A
LED
voltage or high ambient temperature can cause
CAT4109
P
Dmax
LEDN
P
JA
D
) thermal resistance is equal to:
=
is the voltage at the LED pin, and I
=
T
T (
(
J
V
Jmax
= T
to
DD
θ
= T
θ
D
AMB
×
JA
-
JA
, and the ambient temperature,
enter
LEDN
I
T
DD
CA
AMB
JC
= θ
AMB
+ P
) thermal resistance which is
) thermal resistance, which is
) (
D
+
+ P
JC
is high, a resistor can be
)
) of the CAT4109 can be
D
Σ
=
+ θ
(θ
thermal
D
V
(
150
JC
LEDN
θ
JA
CA
JA
J
+ θ
74
is about 74°C/W.
is a function of the
-
×
60
CA
I
LEDN
)
)
shutdown.
=
1
)
2 .
W
D
LEDN
.
In
is
8
RECOMMENDED LAYOUT
Bypass capacitor C1 should be placed as close to the
IC as possible. RSET resistors should be directly
connected to the GND pin of the device. For better
thermal dissipation, multiple via can be used to
connect the GND pad to a large ground plane. It is
also recommended to use large pads and traces on
the PCB wherever possible to spread out the heat.
The LEDs for this layout are driven from a separate
supply (VLED+), but they can also be driven from the
same supply connected to VDD.
Figure 3. Recommended Layout
Characteristics subject to change without notice
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