MP4068 – HIGH PF, NON-ISOLATED, TRIAC DIMMABLE LED DRIVER

MP4068 Rev. 1.01

www.MonolithicPower.com

13

7/30/2015

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2015 MPS. All Rights Reserved.

OPERATION

The MP4068 is a highly integrated and cost-

effective TRIAC dimmable LED driver with a

high power factor (PF). Minimal external

components make the MP4068 a competitive

IC in low-line (120VAC) input, non-isolated

applications, especially for small form factor

applications. Hybrid operation mode achieves

both good dimming performance and an

accurate output current. The power factor is

higher than 0.7 in most applications to eliminate

the harmonic pollution on AC line. The

integrated high-voltage regulator enables fast

start-up without any perceptible delay. The

power de-rating function at high temperatures

protects the IC from thermal damage.

Hybrid Operation Mode

To

achieve

smooth

TRIAC

dimming

performance, the MP4068 implements an MPS

proprietary hybrid operation mode, in which the

IC self-adjusts the internal PWM control mode

between CCM and DCM during different times

of the AC cycle. The hybrid operation mode

actively maintains the latching current and

holding current of the leading edge TRIAC, and

it enables good power factor.

Also, the hybrid operation mode achieves the

small dimming duty condition. The IC works in

CCM during the entire dimming on time when

the dimmer is set to a small dimming duty. The

higher and smoother input current achieves

excellent dimming performance.

Power Supply

The IC is self supplied by the internal high-

voltage regulator (which is drawn from the

drain). The IC starts switching and the internal

high-voltage regulator turns off as soon as the

voltage on

typically). When the voltage on VCC falls below

voltage regulator turns on again to charge the

external VCC capacitor. A small capacitor

(several μF) is recommended. In TRIAC

dimming applications, the internal high-voltage

regulator works only when the dimmer is on and

cannot afford enough power supply for the chip,

so an external charging circuit is recommended

(see Fig. 2).

When the voltage on VCC drops below

and the internal high-voltage regulator re-

charges the VCC capacitor.

VCC

OVF

GND

L

R1

LED+

MP4068

C2

C1

D1

FIGURE 2. VCC Charging Circuit

When OVP occurs, the MP4068 stops working,

and an 18μA internal current source discharges

the VCC capacitor. After VCC drops below

voltage regulator re-charges the VCC capacitor

again. The re-start time can be calculated by the

following equation:

−−

=×

+

×

μ

restart

Vcc

Vcc

Vcc 2.35V

4.65V 2.35V

tC

C

18 A

5mA

Fig. 3 shows the typical waveform with VCC

under-voltage lockout.

VCC

Internal

Voltage

Regulator

Driving

Signal

ON

OFF

FIGURE 3. VCC Under-Voltage Lock Out (UVLO)

Constant Current Operation

The MP4068 is a highly integrated driver. The

internal feedback logic responds to the internal

sample and hold circuit to achieve constant

output-current regulation. The voltage of the

the internal reference (0.195V). When the

reference voltage (which indicates an insufficient

output current), the integrated MOSFET is