EUP3595
With this configuration, two parallel current sources
of equal value provide current to each LED. RSET
should therefore be chosen so that the current through
each output is programmed to 50% of the desired
current through the parallel connected LEDs. For
example, if 30mA is the desired drive current for 2
parallel connected LEDs, RSET should be selected so
that the current through each of the outputs is 15mA.
Other combinations of parallel outputs may be
implemented in similar fashions, such as in Figure 6.
Figure4. EUP3595 LED Current Setting Example
Which Using a DC Voltage to RSET
Table 2. The LED Current vs VADJ With
RADJ=12.5KΩ and RSET=11.5KΩ
0
0.2
18.1
1.6
0.4
16.5
1.8
0.6
14.9
2
0.8
13.3
2.2
1
1.2
10.1
2.5
0
VADJ(V)
ILED(mA)
VADJ(V)
19.7
1.4
8.5
11.7
2.4
0.5
6.9
5.3
3.7
2.1
ILED(mA)
LED Selection
The EUP3595 is designed to drive white-LEDs with a
typical forward voltage of 3.0V to 4.0V. The maximum
LED forward voltage that the EUP3595 can accommo
-date is highly dependant upon VIN and ILEDX (See the
section on Output Current Capability for more
information on finding maximum VLEDX.) For
applications that demand color and brightness
matching, care must be taken to select LEDs from the
same chromaticity group. Forward current matching is
assured over the LED process variations due to the
constant current outputs of the EUP3595.
Figure 6. One Parallel Connected LED
Connecting outputs in parallel does not affect internal
operation of the EUP3595 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 EUP3595 Typical Application Circuit.
Parallel LEDx Outputs for Increased
Current Drive
Outputs LED1 through LED4 may be connected
together in any combination to drive higher currents
through fewer LEDs. For example in Figure 5,
outputs LED1 and LED2 are connected together to
drive one LED while LED3 and LED4 are connected
together to drive a second LED.
Figure 5. Two Parallel Connected LEDs
Figure 7. 4LEDs, LED VF=2.7V, ILED=15mA
DS3595 Ver1.0 Feb. 2007
7
EUTECH [ EUTECH MICROELECTRONICS INC ]
