Micrel, Inc.
MIC4827
Diode
The diode must have a high reverse voltage (150V),
since the output voltage at the CS pin can reach up to
110V. A fast switching diode with lower forward voltage
and higher reverse voltage (150V), such as BAV20WS,
can be used to enhance efficiency.
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
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 (controlled 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
10 F/6.3V
Murata
GRM42-6X5R106K6.3
C1
0.22 F/10V
Murata
GRM39X7R 224K10
R2
3.32M
R1
332k
L1
220 H
Murata
LQH4C221K04
D1
BAV20WS
C
OUT
0.01 F/100V
GRM40X7R103K
5
6
8
7
MIC4827
1
2
3
4
VDD
RSW
REL
GND
SW
CS
VA
VB
3in
2
LAMP
V
IN
3.3V
I
IN
28mA
V
A
– V
B
180V
PP
F
EL
106Hz
Lamp Size
3in
2
V
A
Ð V
B
(50V/div)
V
A
V
B
(50V/div) (50V/div)
TIME (2ms/div)
Figure 5. Typical 100Hz EL Driver for 3in
2
Lamp
July 2009
9
M9999-070709-A
(408) 955-1690
MICREL [ MICREL SEMICONDUCTOR ]
