SC604A
POWER MANAGEMENT
Methods for Setting LED Current
Table 2 - Resistor Value Selection
RSET Value
Nearest kΩ
There are four methods for setting and adjusting the LED current
outlined here. The methods are:
1) RSET only
Standard
Value
% Difference
2) Analog Reference VADJ
3) NMOS switched parallel resistors
4) PWM Input
ILED[mA]
RSET[kΩ]
Standard
Value
0.5
1
931
471
931
470
237
154
93.1
47.5
31.6
24.0
16.5
0.0%
-0.2%
0.0%
-0.6%
-1.0%
0.0%
-0.7%
0.0%
0.0%
Method 1. The most basic means of setting the LED current is
with a resistor connected from ISET to GND, as shown in the
application circuit on Page 1. The resistor RSET establishes the
reference current needed for a constant LED current. Values of
RSET for a fixed LED current are given in Table 2 and also in the
below graph, “Typical RSET Resistance vs. LED Current”. Methods
2 and 3 on page 10 are for setting the LED current allow for
brightness control.
2
237
3
155
5
94.0
47.5
31.83
24.0
16.5
10
15
20
30
Typical RSET Resistance vs. LED Current
1000
950
900
850
800
750
700
650
600
550
500
450
400
350
300
250
200
150
100
50
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
5.5
6
6.5
7
7.5
8
8.5
9
9.5 10
LED Current [mA]
2005 Semtech Corp.
www.semtech.com
9
SEMTECH [ SEMTECH CORPORATION ]
