TK11850LTL TOKO [TOKO, Inc], TK11850LTL Datasheet - Page 11

• Manufacturer Part Number: TK11850LTL
• Description: WHITE LED DRIVER
• Manufacturer: TOKO [TOKO, Inc]

May 2001 TOKO, Inc.
2. PWM Dimming
Apply the PWM signal to the EN Terminal (Pin no. 8). In this case, a signal frequency of approximately120 Hz is adequate.
The average current of the LED changes due to the On/Off cycle of the IC, which follows the duty cycle of the PWM signal.
Set the PWM signal at a high level over 2 V and a low level under 0.6 V, with a driving current over 2 mA.
The PWM dimming LED current follows the PWM signal. (As shown above)
The average LED current is obtained from the formula below. The graph below shows an example with I
a Duty Cycle up to 100%.
GND
V IN
C IN
R SC
L
D
C OUT
V OUT
EXT
V IN
I S
0.1 V
D
U
+
-
T
1
I S COMP
4
9
8
7
6
5
3
2
1
Y
0
I
0
0
0
0
0
0
0
0
0
LED
0
(
%
)
vs. DUTY
CLK
I
L
E
D
2
1
1
1
1
1
Q
8
6
4
2
0
8
6
4
2
0
(
0 .
0 .
0 .
0 .
m
0 .
0 .
0 .
0 .
0 .
0 .
) A
S
R
V LED
(LED CURRENT)
Cx
CLK
0.86 V
0.3 V
DIMMING (CONT)
OSC
I
BAND GAP REFERENCE
LED(AVG)
I LED
CLK
0.525 V
= I
V REF
ERROR
COMP
LED(MAX)
+
-
R LED
* Duty
7
8
EN
GND
C X
V FB
12
20
18
16
14
10
100
4
0
8
2
6
0
ON/OFF
DUTY CYCLE OF INPUT PWM SIGNAL
C X
(Applied to On/Off pin.)
20
LED CURRENT (I LED ) vs.
PWM SIGNAL
LED CURRENT
DUTY CYCLE (%)
40
LED CURRENT CURVE vs. PWM SIGNAL CURVE
60
Ton
Toff
T
TK11850L
80
LED(MAX)
fdim = 1 / T = 120 Hz
Duty (%) = (Ton * 100) / T
100
(20 mA) at
LED SETTING
Page 11
CURRENT
2.0 V
0.6 V