MP4050 – NON-ISOLATED, HIGH BRIGHTNESS, LED DRIVER

MP4050 Rev.1.02

www.MonolithicPower.com

14

1/18/2016

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Sense Resistor

The sense resistor needs to choose properly for

better output current regulation. The right

resistor guarantees stable output current

regulation

in

high

temperature

and

low

temperature conditions. The sense resistor

should have 1% tolerance. It is even better to

parallel two 1% tolerance resistors to decrease

the resistance value error further. Sense

resistor with ± 400PPM/ ℃

temperature

coefficient can be used for better output current

regulation

in

high

temperature

and

low

temperature.

Feedback Resistor

Feedback resistor is used to detect the fault

operation mode such as open lamp or short

lamp conditions. Figure 7 shows the feedback

resistors connection.

MP4050

VCC

PRO

GND

L

R2

R3

Figure 7: Feedback resistor connection

MP4050 is integrated with open lamp protection

and the over voltage protection point can be

designed as following function.

OVP

PRO

D

R2 R3

VV

(1

) V

R2



 



drop.

The upper feedback resistor (R3) is suggested

to be larger than 100kΩ to avoid the efficiency

reduction in application. And the 1% tolerance

type is recommended to use as feedback

resistor to achieve accurate protection such

over voltage protection when open lamp.

The feedback resistor R2 could be sized down

to SMD 0603 package. Considering the

dielectric

withstanding

voltage,

R3

is

recommended to have a minimum size of SMD

1206 package.

Dummy Load

Dummy load is recommended to regulate the

output voltage low than over voltage protection

point when open lamp condition. The dummy

load is used to consume the power transferred

to output capacitor when hiccup mode without

any power consumption.

Normally less than 1mA dummy load is

suggested which not deteriorate the system

efficiency and also guarantees the normal open

lamp protection.

PRO Decoupling Capacitor

One decoupling cap is recommended to parallel

between the PRO pin and GND pin. The

floating GND pin is sensitive to the voltage

noise spike in high side Buck solution. One

ceramic capacitor is suggested to use as

decoupling capacitor to decouple the voltage

noise for more stable operation.

Around 30pF PRO decoupling capacitor could

be used in SOIC8 package application and as

for smaller package TSOT23-5, no less than

100pF decoupling capacitor is recommended.

Figure 8 shows the PRO pin decoupling

capacitor connection.

MP4050

VCC

PRO

GND

L

R2

R3

Figure 8: Decoupling capacitor

PRO Time Constant

MP4050 detects the PRO pin voltage to judge

the fault condition when internal MOSEFET

turns off. Long rise time of the PRO pin voltage

affects MP4050 normal output voltage sample

which can not judge the open lamp immediately.

The PRO pin time constant (τ) should satisfy

the following expression to guarantee the

normal open lamp protection.