MP4688 – 80V INPUT, 1A HIGH POWER LED DRIVER
Where RESR is the equivalent series resistance
(ESR) value of the output capacitor.
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.
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:
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.
z
z
z
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
cycle operation (when VOUT/VIN>65%) and very
high frequency (over 1.5MHz) applications.
The bootstrap diode can be a low cost one
such as IN4148 or BAT54.
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.
5V
BS
MP4560
MP4688
SW
Figure 2—External Bootstrap Diode
Layout Consideration
Specifications
Parameter
Symbol
VIN
Value
4.5 to 75
5
Units
V
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.
Input Voltage
Enable/Dimming
LED Current
EN/DIM
ILED
V
730
mA
Over
Current
OCP
3.2
A
Protection
Reference schematic
MP4688
EN
1
8
7
6
5
FB
N/C
VIN
BST
GND
EN
DIM
SW
R3
NS
2
3
4
DIM
VIN
/100V
C2
/100V
LED+
LED_
R4
0
D1
C1
C3
C5
NC
C7
NC
GND
R1
R2
MP4688 Rev. 1.12
3/28/2012
www.MonolithicPower.com
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© 2012 MPS. All Rights Reserved.
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