MIC4827
Micrel
Diode
The application circuit specifies the 1N4148 or equivalent. It
has a forward current of 150mA and a typical forward voltage
of 950mV. For applications that are not cost driven, a fast-
switching diode with lower forward voltage and higher re-
verse voltage can be used to enhance the efficiency, such as
BAV20WS or BAS20W.
Output Capacitor
Low ESR capacitors should be used at the regulated boost
output (CS pin) of the MIC4827 to minimize the switching
output ripple voltage. Selection of the capacitor value will
depend upon the peak inductor current, inductor size, and the
load. MuRata offers the GRM42-6 series with up to 0.047µF
at 100V, with a X7R temperature coefficient in 1206 surface-
mount package. Typically, values ranging from 0.01µF to
0.1µF at 100V can be used for the regulated boost output
capacitor.
L1
220µH
D1
Murata
Vishay Telefunken
LQH4C221K04
MCL4148
C
OUT
0.01µF/100V
GRM40X7R103K
5
6
8
Application Information
Inductor
In general, smaller value inductors, which can handle more
current, are more suitable to drive larger size lamps. As the
inductor value decreases, the switching frequency (con-
trolled by R
SW
) should be increased to avoid saturation or the
input voltage should be increased. Typically, inductor values
ranging from 220µH to 560µH can be used. Murata offers the
LQH3C series up to 560µH and LQH4C series up to 470µH,
with low DC resistance. A 220µH Murata (LQH4C221K04)
inductor is recommended for driving a lamp size of 3 square
inches. It has a maximum DC resistance of 4.0Ω.
Pre-designed Application Circuit
Li-Ion Battery
V
IN
3.0V to 4.2V
C2
10µF/6.3V
Murata
GRM42-6X5R106K6.3
C1
0.22µF/10V
Murata
GRM39X7R 224K10
R1
R2
3.32M
332k
MIC4827
1
2
3
VDD
RSW
REL
SW
CS
VA
4
7
GND
VB
3in
2
LAMP
V
IN
3.3V
I
IN
28mA
V
A
–V
B
180V
PP
F
EL
106Hz
Lamp Size
3 in
2
V
A
— V
B
(50V/div)
V
B
(50V/div)
V
A
(50V/div)
TIME (2ms/div)
Figure 5. Typical 100Hz EL Driver for 3in
2
Lamp
MIC4827
8
January 2005
MICREL [ MICREL SEMICONDUCTOR ]
