EUP2794
Power Dissipation
The power dissipation (PDISSIPATION) and junction
temperature (TJ) can be approximated with the
equations below. PIN is the power generated by the
1.5x charge pump, PLED is the power consumed by the
LEDs, PPOUT is the power provided through the POUT
pin, TA is the ambient temperature, and θJA is the
junction-to-ambient thermal resistance for the
QFN-16 package. VIN is the input voltage to the
EUP2794, VDX is the LED forward voltage, IDX is the
programmed LED current, and IPOUT is the current
drawn through POUT
.
P
=
= P − P
IN LED
− P
POUT
DISSIPATION
1.5× V 41
[
×
(
+ I
)]
−
(
1.5× V × I )
IN DX
POUT
× θ
IN POUT
T = T
+
(P
)
J
A
JA
Figure 7. Efficiency vs VIN
4 LEDS, VLED=3.4V,ILED=15mA
The junction temperature rating takes precedence
over the ambient temperature rating. The EUP2794
may be operated outside the ambient temperature
rating, so long as the junction temperature of the
device does not exceed the maximum operating rating
of 100°C. The maximum ambient temperature rating
must be derated in applications where high power
dissipation and/or poor thermal resistance causes the
junction temperature to exceed 100°C.
Figure 8. PIN vs VIN
4 LEDS, 2.5≤ VDX ≤ 3.4V, IDX=15mA
DS2794 Ver0.5 Mar. 2006
12
EUTECH [ EUTECH MICROELECTRONICS INC ]
