MP4001

– UNIVERSAL INPUT HIGH BRIGHTNESS WLED DRIVER

MP4001 Rev 1.02

www.MonolithicPower.com

11

5/1/2018

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© 2018 MPS. All Rights Reserved.

LED

sense

VREF

I

2R



The zero-current detection is realized at DRIVE

pin by sensing the MOSFET drain dv/dt current

through the Q1’s miller cap. When the current

of freewheeling diode goes to zero, Q1 drain

and starts oscillation caused by the inductor

minimum value, the dv/dt current through the

miller cap changes from negative to zero. At

this time, the MP4001 turns on Q1. As a result,

MP4001 turns on Q1 when the inductor current

goes to zero and Q1 drain voltage is at the

minimum. MP4001 controls the buck converter

operation in current boundary conduction mode.

It is usually recommended to add a 10pF cap

between the drain and source of Q1 to help for

the zero current detection.

A cap Cout can be used in parallel with the LED

string to reduce the current ripple.

Such boundary operation mode can minimize

the

Q1

turn

on

loss

and

eliminate

the

freewheeling diode reverse recovery loss so

that high switching frequency is possible to

reduce passive

components’ size. Furthermore,

the required inductance value is small, which

can help further inductor size reduction.

Brightness Dimming Control

MP4001 can employs a burst dimming control

scheme so that a DC signal can control the

dimming by varying the DC voltage level, or an

external PWM signal can control the dimming

by varying the duty cycle.

For the DC input dimming control, a voltage

from 0V to 2.42V is recommended to connect to

the DIM pin. 2.42V and above is for the 100%

brightness. 120mV and below is for the 5%

from BOS pin to GND to program the burst

2.42V

Figure 4: DC Burst Dimming

For the PWM input dimming control, a 100Hz to

2kHz PWM signal is recommended to connect

to the DIM pin. BOS pin is connected to GND

through a 300k

Ω resistor, setting about 1.2V

reference for the PWM input logic signal. PWM

input high will make the IC switching. PWM

input low turns off the IC.

While doing dimming, the dimming high signal

force the DRIVE signal high and the dimming

low signal force the DRIVE signal to low. There

will be a case that the dimming low interval is

too small for Inductor current reaching zero, the

CCM will be observed. So the rectifying diode

(D in Typical Application) must be Ultra-Fast

diode or Super-Fast diode.

CCM

Figure 5: CCM in Large Dimming Duty

For application that do not need burst dimming

control, open DIM pin and short BOS pin to

GND

Frequency Setting and Inductor Design

In case the zero-current detection circuit fails,

which can happens in start up with a large

output cap and in output short condition, a

maximum off time of about 1.7ms is applied to

make sure MP4001 is still in operation and the

short current doesn’t run away.