HV857
HV857
High Voltage EL Lamp Driver for
Low Noise Applications
Features
❏
Patent pending audible noise reduction
❏
Patent pending lamp aging compensation
❏
190V
PP
output voltage for higher brightness
❏
Patented output timing for high efficiency
❏
Single cell lithium ion compatible
❏
150nA shutdown current
❏
Wide input voltage range 1.8V to 5.0V
❏
Separately adjustable lamp and converter frequencies
❏
Output voltage regulation
❏
Split supply capability
General Description
The Supertex HV857 is a high voltage driver designed for driving
Electroluminescent (EL) lamps of up to 5 square inches. The
input supply voltage range is from 1.8V to 5.0V. The device uses
a single inductor and a minimum number of passive components.
The nominal regulated output voltage that is applied to the EL
lamp is
±
95V. The chip can be enabled/disabled by connecting
the resistor on R
sw-osc
to V
DD
/ground.
The HV857 has two internal oscillators, a switching MOSFET,
and a high voltage EL lamp driver. The frequency for the
switching MOSFET is set by an external resistor connected
between the R
sw-osc
pin and the supply pin V
DD
. The EL lamp
driver frequency is set by an external resistor connected be-
tween R
EL-osc
pin and the V
DD
pin. An external inductor is
connected between the L
X
and V
DD
pins or V
IN
for split supply
applications. A 0.003-0.1µF capacitor is connected between C
s
and ground. The EL lamp is connected between V
A
and V
B
.
The switching MOSFET charges the external inductor and
discharges it into the capacitor at C
s
. The voltage at C
s
will start
to increase. Once the voltage at C
s
reaches a nominal value of
95V, the switching MOSFET is turned OFF to conserve power.
The outputs V
A
and V
B
are configured as an H bridge and are
switching in opposite states to achieve
±
95V across the EL lamp.
Applications
❏
LCD backlighting
❏
Mobile cellular phones
❏
PDAs
❏
Handheld wireless communication products
❏
Global Positioning Systems (GPS)
Typical Application
ON=V
DD
OFF=0
Regulated Voltage=V
DD
Enable Signal
1
V
DD
2
R
SW-osc
V
A
V
B
8
EL Lamp
7
+
V
DD
=V
IN
_
C
IN
3
R
EL-osc
4
Gnd
C
S
6
L
X
5
L
X
C
S
HV857MG
11/14/01
Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability
indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to
workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the
Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.
1
SUPERTEX [ Supertex, Inc ]
