MP4050A – NON-ISOLATED, HIGH-BRIGHTNESS LED DRIVER, WITH ENHANCED THERMAL FEATURE

MP4050A Rev. 1.01

www.MonolithicPower.com

12

1/14/2016

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OPERATION

The MP4050A is a non-isolated, cost-effective,

high-efficiency converter designed to drive high-

brightness LEDs from a universal AC grid input

or DC input. As shown in the typical application

diagram (see Fig. 1), the regulator is designed

to operate with a minimum number of external

components.

Start-Up and Under-Voltage Lockout (UVLO)

Initially, the chip is self-supplied by the internal

high-voltage VCC regulator (which is drawn

from DRAIN). The IC starts switching and the

internal high-voltage regulator turns off as soon

below

the

internal

high-voltage

regulator turns on again to charge the external

VCC capacitor. Finally, VCC is regulated at

A small capacitor with several μF capacitances

is enough to hold on to the VCC supply voltage.

Also, a smaller capacitor reduces component

stops working and the internal high-voltage

regulator re-charges the VCC capacitor.

When fault conditions occur (such as open LED

protection or over-temperature protection), the

MP4050A stops working, and an 18µA internal

sink current source discharges the VCC capacitor.

voltage regulator recharges the VCC capacitor

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

following equation,

NOR

PRO

OFF

PRO

RESTART

VCC

VCC

VCC

VCC

VCC

VCC

tC

C

18 A

5mA











Fig. 2 shows the typical waveforms with VCC

under-voltage lockout.

FIGURE 2. VCC Under-Voltage Lockout (UVLO)

Constant-Current Operation

The MP4050A is a fully integrated regulator.

The internal feedback logic responds to the

internal sample and hold circuit to achieve

constant output-current regulation. The voltage

the reference voltage (which indicates an

insufficient output current). Then the integrated

MOSFET is turned on. The on period is

determined by the peak current limit. After the

on period elapses, the integrated MOSFET is

turned off (see Fig. 3).

Thus, by monitoring the internal sampling

capacitor voltage, the output current can be

regulated. The output current is determined by

the following equation:

REF

OUT

S

V

I

R



The peak inductor current at normal operation

can be obtained with the following equation:

LIMIT

PK

S

V

I

R



from SOURCE to GND.