LP3359 Datasheet, PDF (7/9 Pages) Lowpower Semiconductor inc – High performance, Current Source For Parallel White-LED Driver

LP3359
Connecting outputs in parallel does not affect internal
operation of the LP3359 and has no impact on the Electrical
Characteristics and limits previously presented. The available
diode output current, maximum diode voltage, and all other
specifications provided in the Electrical Characteristics table
apply to parallel output configurations, just as they do to the
standard 4-LED application circuit.
Power Consumption
It is recommended that power consumed by the circuit (VIN ×
IIN) be evaluated rather than power efficiency. Figure 7 shows
the power consumption of the LP3359 Typical Application
Circuit.
Where T is the maximum junction temperature, T is the
ambient temperature, and θJA is the junction -to-ambient
thermal resistance of the specified package. The LP3359 come
in the DFN-8 package that has a junction-to-ambient thermal
resistance (θJA)equal to 50℃/W.This value of θJA is highly
dependant upon the layout of the PC board. The actual power
dissipated by the LP3359 follows the equation:
Where N equals the number of active outputs, VLEDX is the
LEDX LED forward voltage, and ILEDX is the current supplied
to the LEDX diode by the LP3359. Power dissipation must be
less than that allowed by the package. Please refer to the
Absolute Maximum Rating of the LP3359.
Input Capacitor Selection
The LP3359 is designed to run off of a fixed input voltage.
Depending on the stability and condition of this voltage rail, it
may be necessary to add a small input capacitor to help filter
out any noise that may be present on the line. In the event that
filtering is needed, surface mount multi-layer ceramic
capacitors are recommended. These capacitors are small and
inexpensive. A capacitance of 0.1µF is typically sufficient.
Figure 7. 4LEDs, LED VF=2.7V, ILED=15mA Power Dissipation
The maximum allowable power dissipation that this
package is capable of handling can be determined as
follows:
LP3359-datasheet Ver.1.1 Nov.-2005
7 -7