MP4050 – NON-ISOLATED, HIGH BRIGHTNESS, LED DRIVER

MP4050 Rev.1.02

www.MonolithicPower.com

12

1/18/2016

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© 2016 MPS. All Rights Reserved.

The peak current can be obtained as follow:

Peak

0.45V

I

R1



R1 is the sense resistor.

Minimum Operating Frequency Limit

MP4050

incorporates

minimum

operating

frequency (22kHz) to eliminate the audible

noise when frequency is less than 20kHz.

When operating frequency is less than 22kHz,

the internal peak current regulator will decrease

the peak current value to keep the operating

frequency constant about 22kHz.

If the inductance value is too large to make the

operating

frequency

reach

the

minimum

operating frequency, the converter will enter the

CCM. And the converter works in DCM when

operating frequency is larger than 22kHz.

Minimum Off Time Limit

A minimum off time limit is implemented. During

the normal operation, the minimum off time limit

is 4.7us, and during the start up period, the

minimum off time limit is shortened gradually

from 18.8μs, 9.4μs to 4.7μs (Shown as Figure

4). Each minimum off time keeps 128 switching

cycle. This soft start function enables safe start-

up.

≥18.4us

≥9.4us

≥4.7us

Driver

128 switchingcycle

128 switchingcycle

Thermal Shutdown (TSD)

To prevent MP4050 from any thermal damage,

MP4050 shuts down switching cycle when the

junction temperature exceeds 150

C. As soon

as the junction temperature drops below 90

C,

the power supply resumes operation. During

by the internal high voltage regulator.

Open Lamp Protection

when MOSFET turns off, MP4050 stops

working and a re-start cycle begins. Open lamp

protection is hiccup mode. MP4050 monitors

the PRO pin voltage continuously and the VCC

voltage discharges and charges repeatedly.

MP4050

resumes

work

until

the

fault

disappears.

Short Lamp Protection

when MOSFET turns off, MP4050 stops

working and a re-start cycle begins. Short lamp

protection is hiccup mode. MP4050 monitors

the PRO pin voltage continuously and the VCC

voltage discharges and charges repeatedly.

MP4050

resumes

work

until

the

fault

disappears.

Leading Edge Blanking

There are parasitic capacitances in the circuit

which can cause high current spike during the

turn-on of the internal MOSFET. In order to

avoid

the

premature

termination

of

the

switching pulse, an internal Leading Edge

Blanking (LEB) unit is employed. During the

blanking time, the current comparator is

disabled and blocked from turning off the

internal MOSFET. Figure 5 shows the leading

edge blanking.

t

Figure 5: Leading Edge Blanking (LED)