MIC4827_05 Datasheet, PDF (8/13 Pages) Micrel Semiconductor – Low Input Voltage, 180VPP Output Voltage, EL Driver

MIC4827
Micrel
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
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.
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
R2
3.32M
L1
220µH
D1
Murata _{Vishay Telefunken}
LQH4C221K04 _MCL4148
MIC4827
1 _VDD
R1 ₂
RSW
332k
3
REL
4
GND
SW ⁵
6
CS
8
VA
7
VB
C_OUT
0.01µF/100V
GRM40X7R103K
3in² LAMP
V_IN
3.3V
I_IN
28mA
V_A–V_B
180V_PP
F_EL
106Hz
Lamp Size
3 in²
MIC4827
TIME (2ms/div)
Figure 5. Typical 100Hz EL Driver for 3in² Lamp
8
January 2005