MP4688 – 80V INPUT, 1A HIGH POWER LED DRIVER

MP4688 Rev. 1.12

www.MonolithicPower.com

9

3/28/2012

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

© 2012 MPS. All Rights Reserved.

(ESR) value of the output capacitor.

External Bootstrap Diode

An external bootstrap diode may enhance the

efficiency of the LED driver. In below cases, an

external BST diode is recommended from the

5V to BST pin:

There is a 5V rail available in the system;

VIN is no greater than 5V;

VOUT is between 3.3V and 5V;

This diode is also recommended for high duty

high frequency (over 1.5MHz) applications.

The bootstrap diode can be a low cost one

such as IN4148 or BAT54.

MP4560

SW

BS

5V

MP4688

Figure 2—External Bootstrap Diode

Layout Consideration

It is essential to place the input decoupling

capacitor, catch diode and the MP4688 (VIN pin,

SW pin and PGND) as close as possible, with

traces that are very short and fairly wide. This

can help to greatly reduce the voltage spike on

SW node, and lower the EMI noise level as well.

Try to run the feedback trace as far from the

inductor and noisy power traces as possible. It

is often a good idea to run the feedback trace

on the side of the PCB opposite of the inductor

with a ground plane separating the two.

To help to improve the thermal conduction, a

grid of thermal vias can be created right under

the exposed pad. It is recommended that they

be small (15mil barrel diameter) so that the hole

is essentially filled up during the plating process,

thus aiding conduction to the other side. Too

large a hole can cause ‘solder wicking’

problems during the reflow soldering process.

The pitch (distance between the centers) of

several such thermal vias in an area is typically

40mil.

Reference design

Street lighting and flat panel lighting are

transiting to more efficient sources of light. LED

light source will become the trend in the near

future. This reference design provides a flexible

solution for street lighting and flat panel lighting

application by utilizing MP4688 featuring high

reliability, high efficiency, and accurate current

regulation.

Specifications

Parameter

Symbol

Value

Units

Input Voltage

VIN

4.5 to 75

V

Enable/Dimming

EN/DIM

5

V

LED Current

730

mA

Over

Current

Protection

OCP

3.2

A

Reference schematic

R1

C1

/100V

/100V

C2

C3

R4

0

D1

NS

R3

8

1 FB

N/C

VIN

BST

SW

DIM

EN

GND

MP4688

2

3

4

7

6

5

LED_

LED+

DIM

EN

VIN

GND

C5

NC

C7

NC

R2