TK11850L
APPLICATION CIRCUIT (3 LEDs in Series)
• Input Voltage: 2.7 V
• LED Current: 20 mA
• On/Off: Pin Number 8 (EN Pin)
LED Current (ILED) is set by RLED.
ILED doesn’t depend on VIN because ILED
is controlled by the feedback circuit.
VIN
CIN
4.7 µF
GND
RSC
0.27 Ω
VIN 0.1 V
IS
IS COMP
+
-
L 22 uH
D31FU
TOKO
SB07-03C
SANYO
EXT
VOUT
BAND GAP REFERENCE
OSC
0.86 V
Cx 0.3 V
CLK
CLK
S
Q
R
ERROR
COMP
VREF
0.525 V
COUT
2.2 uF
VLED
ILED
TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)
TA = 25 °C, unless otherwise specified.
LED Current and Efficiency Characteristics
EN
8
ON/OFF
CX
7
GND
VFB
CX
82 pF
RLED
27 Ω
VIN (V)
2.5
IIN (mA)
115.9
VLED (V)
10.38
ILED (mA)
19.41
EF LED (%)
69.52
L: D31FU, 22 mH
Toko Part Number: 888FU-220M
2.7
106.9
10.38
3.0
95.4
10.38
19.49
19.52
70.09
70.83
EF LED (%) = 100 * VLED * ILED / VIN* IIN
3.5
79.1
10.38
19.52
73.19
4.5
59.2
10.39
19.56
76.26
6.0
42.9
10.39
19.60
79.04
EF LED vs. VIN
100
80
60
40
20
0
0
2
4
6
8
VIN (V)
ILED vs. VIN
20
18
16
14
12
10 0
2
4
6
8
VIN (V)
Page 8
May 2001 TOKO, Inc.