MAX4990E Maxim Integrated Products, MAX4990E Datasheet - Page 12

• Manufacturer Part Number: MAX4990E
• Description: High-Voltage +-15kV ESD-Protected Electroluminescent Lamp Driver
• Manufacturer: Maxim Integrated Products

lamp outputs. A slow turn-on effect is produced by dri-
ving EN high. Slow turn-on/-off time is related by the fol-
lowing equation:
For this equation to be valid, R
≤ 1.3.
C
the high-voltage source for the EL lamp. Connect a
3.3nF capacitor from CS to GND and place as close to
the CS input as possible. When using an inductor value
larger than 220µH, it may be necessary to increase the
C
ranging from 3.3nF to 6.8nF is recommended.
The MAX4990E EL lamp output frequency is set by
connecting a capacitor from the EL input to GND
together with a resistor from SLEW to GND or by driving
the EL input with an external clock (0 to +1.5V). The EL
lamp output frequency is related to the C
by the following equation:
For example, an R
value of 1000pF equals an EL lamp output frequency of
F
The boost converter switching frequency is set by con-
necting a capacitor from the SW input to GND, together
with the resistance from the SLEW input to GND, or driving
the SW input with an external clock (0 to +1.5V). The
switching frequency of the boost converter is related to the
capacitor from SW to GND by the following equation:
High-Voltage, ±15kV ESD-Protected
Electroluminescent Lamp Driver
12
EL
CS
CS
= 217Hz.
. For a LX = 470µH and C
______________________________________________________________________________________
is the output of the boost converter and provides
t
t
ON
OFF
f
f
EL
SW
SLEW
= 2.6 x R
= 1.2 x R
=
=
R
R
C
C
SLEW
C
= 375kΩ and a C
SLEW
SW
0 0817
CS
EL
.
DIM
3 61
DIM
.
Capacitor Selection
Capacitor Selection
Capacitor Selection
×
×
C
C
x C
x C
LAMP
EL
SW
DIM
DIM
DIM
/R
= 20nF, a C
SLEW
EL
EL
capacitor
capacitor
must be
CS
Connect the SW input to GND to turn the switch oscilla-
tor of the boost converter off. Although the optimal f
depends on the inductor value, the suggested f
range is 20kHz to 150kHz.
Note: Driving SW with a logic-high causes LX to be dri-
ven to GND. Keeping SW high shorts LX to GND, caus-
ing the internal die temperature to increase. The
MAX4990E is protected by entering a thermal-shutdown
state. (See the Thermal Short-Circuit Protection section.)
Bypass V
the IC as possible and a 4.7µF ceramic capacitor as
close to the inductor as possible
Connect a diode, D
the boost voltage on CS. The diode should be a fast-
recovery diode that is tolerant to +150V.
EL lamps have a capacitance of approximately 2.5nF to
3.5nF per square inch. The MAX4990E effectively
charges capacitance ranging from 2nF to 20nF.
Keep PCB traces as short as possible. Ensure that
bypass capacitors are as close to the device as possi-
ble. Use large ground planes where possible.
PROCESS: BiCMOS-DMOS
DD
with a 0.1µF ceramic capacitor as close to
Applications Information
1
, from the LX node to CS to rectify
C
B
Chip Information
Capacitor Selection
EL Lamp Selection
www.DataSheet4U.com
Diode Selection
PCB Layout
SW
SW