RT9378 RICHTEK [Richtek Technology Corporation], RT9378 Datasheet - Page 8

• Manufacturer Part Number: RT9378
• Description: 4 CHs 100mA x1/x1.5/x2 Charge Pump White LED Driver
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9378
Thermal Considerations
For continuous operation, do not exceed absolute
maximum operation junction temperature. The maximum
power dissipation depends on the thermal resistance of
IC package, PCB layout, the rate of surroundings airflow
and temperature difference between junction to ambient.
The maximum power dissipation can be calculated by
following formula :
P
Where T
temperature, T
the junction to ambient thermal resistance.
For recommended operating conditions specification of
RT9378, The maximum junction temperature is 125°C.
The junction to ambient thermal resistance θ
dependent. For WQFN-12L 2x2 packages, the thermal
resistance θ
single layer thermal test board. The maximum power
dissipation at T
formula :
P
WQFN-12L 2x2 packages
The maximum power dissipation depends on operating
ambient temperature for fixed T
resistance θ
derating curves allows the designer to see the effect of
rising ambient temperature on the maximum power
allowed.
www.richtek.com
8
D(MAX)
D(MAX)
Figure 2. Derating Curves for RT9378 Packages
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
= ( T
= (125°C − 25°C) / (165°C/W) = 0.606W for
0
J(MAX)
J(MAX)
JA
JA
10 20 30 40 50 60 70 80 90 100 110 120
. For RT9378 packages, the Figure 2 of
A
is 165°C/W on the standard JEDEC 51-3
A
is the ambient temperature and the θ
is the maximum operation junction
= 25°C can be calculated by following
− T
Ambient Temperature (°C)
A
) / θ
JA
J(MAX)
Single Layer PCB
and thermal
JA
is layout
JA
is
Layout Considerations
The RT9378 is a high-frequency switched-capacitor
converter. Careful PCB layout is necessary. For best
performance, place all peripheral components as close to
the IC as possible. Place CIN, COUT, CFLY1, and CFLY2
near to VIN, VOUT, CP1, CN1, CP2, CN2, and GND pin
respectively. A short connection is highly recommended.
The following guidelines should be strictly followed when
designing a PCB layout for the RT9378.
The exposed GND pad must be soldered to a large
ground plane for heat sinking and noise prevention. The
throughhole vias located at the exposed pad is
connected to ground plane of internal layer.
VIN traces should be wide enough to minimize
inductance and handle the high currents. The trace
running from battery to chip should be placed carefully
and shielded strictly.
Input and output capacitors must be placed close to the
part. The connection between pins and capacitor pads
should be copper traces without any through-hole via
connection.
The flying capacitors must be placed close to the part.
The traces running from the pins to the capacitor pads
should be as wide as possible. Long traces will also
produce large noise radiation caused by the large dv/dt
on these pins. Short trace is recommended.
All the traces of LED and VIN running from pins to LCM
module should be shielded and isolated by ground plane.
The shielding prevents the interference of high frequency
noise coupled from the charge pump.
Output capacitor must be placed between GND and
VOUT to reduce noise coupling from charge pump to
LEDs.
DS9378-03 April 2011