11

SANKEN ELECTRIC CO., LTD.

LC5200-DS, Rev. 6.0

Off-Line LED Driver ICs

LC5200 Series

Comp2 inverts its output (see point A in figure 4). This resets the

output Q of the RS flip-flop. After a turn-off signal is transmitted

from the AND gate to the logic, to the gate driver, and finally to

the internal power MOSFET, the power MOSFET turns off. At

the same time, an internal MOS switch, connected to the PWM

decreases to less than 2 V, the comparator for the off-time,

Comp1, inverts and the Q output of the RS flip-flop is set. Then

between the REF and PWM pins).

expires and the power MOSFET turns on. After that, the opera-

tion reverts to the initial state, shown as point B in figure 4.

regulator directly. It is necessary to pay attention to these factors.

Current Value Setting for Dimming Control

The LC5200 series allows constant current control using the

internal PWM control, an external PWM signal, or a combination

of both of them.

Using Internal PWM Dimming

The LC5200 series has a built-in PWM constant current control

circuit, and thus can achieve a constant current drive system for

the LED string, while requiring few external components. The

lated as follows:

=

(1)

The LC5200 series allows external adjustment of the current

flowing through the LED string, using either of the following

methods:

• Adjusting the analog voltage on the REF pin (figure 6A)

• Inputting the analog voltage integrated PWM signal through a

low pass filter, LPF, to the REF pin (figure 6B)

However, the dimming control by adjusting the REF pin voltage

can not set the output current to zero. When controlling to zero

current, an external signal and external circuit are needed to set

the PWM pin voltage to low.

SEN

GND

REG

PWM

REF

SEN

GND

REG

PWM

REF

LC5200

PWM

Signal

LPF

LC5200

50

200

R

400

600

800

1000

20

10

5

2

1

C

PWM

= 470 pF

C

PWM

= 220 pF

C

PWM

= 100 pF

C

PWM

= 47 pF

C

PWM

= 22 pF

C

PWM

= 10 pF

Figure 6. Dimming Application Circuits with Internal PWM Control

(A) Analog Control

(B) Integrated PWM Control