mic3230 Micrel Semiconductor, mic3230 Datasheet - Page 8

• Manufacturer Part Number: mic3230
• Description: Constant Current Boost Controller For Driving High Power Leds
• Manufacturer: Micrel Semiconductor

Functional Description
A constant output current converter is the preferred
method for driving LEDs. Small variations in current have
a minimal effect on the light output, whereas small
variations in voltage have a significant impact on light
output. The MIC323x family of LED drivers are specifically
designed to operate as constant current LED Drivers and
the typical application schematic is shown in Figure 1.
The MIC323x family are designed to operate as a boost
controller, where the output voltage is greater than the
input voltage. This configuration allows for the design of
multiple LEDs in series to help maintain color and
brightness. The MIC323x family can also be configured as
a SEPIC controller, where the output voltage can be either
above or below the input voltage.
between 6V and 45V, to help accommodate for a diverse
range of input voltage applications. In addition, the LED
current can be programmed to a wide range of values
through the use of an external resistor.
RADJ
The MIC3230/1/2 have a very wide input voltage range,
Micrel, Inc.
January 2009
VOUT
LED
LED
SYNC
COMP
IADJ
VIN
EN
FS
0.25V
LDO
SYNC
FS
VDD
10k
VRAMP Out
Figure 2. MIC3230 Functional Block Diagram
T
Clock Out
VDD
V
V
S
This provides
C
VRAMP IN
Internal VBIAS
ISLOPE COMP OUT
Ai = 1.4V
S
R
8
Ai
Q
design flexibility in adjusting the current for a particular
application need.
The MIC3230/1/2 features a low impedance gate driver
capable of switching large MOSFETs.
impedance helps provide higher operating efficiency.
The MIC323x family can control the brightness of the
LEDs via its PWM dimming capability. Applying a PWM
signal (up to 500Hz) to the PWMD pin allows for control of
the brightness of the LED.
Each member of the MIC323x family employs peak current
mode control.
advantages over voltage mode control in the following
manner. Current mode control can achieve a superior line
transient performance compared to voltage mode control
and through small signal analysis (not shown here),
current mode control is easier to compensate than voltage
mode control, thus allowing for a less complex control loop
stability design. Figure 2 shows the functional block
diagram.
OVP PWMD
Control
ISLOPE COMP
0.45V
T
Leading Edge
250µa/T
Blanking
Peak current mode control offers
DRV
IS
GND
RSLC
VIN
M9999-011409-A
Q1
RCS
L1
MIC3230/1/2
This low
C5
VOUT