HV857
Low Noise, High Voltage EL Lamp Driver IC
Features
Patented audible noise reduction
Patented lamp aging compensation
190 V
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
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Output voltage regulation
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Split supply capability
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Available in MSOP-8 and DFN-8 packages
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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 RSW-Osc to VDD/GND.
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
RSW-Osc pin and the supply pin VDD. The EL lamp driver
frequency is set by an external resistor connected between REL-
Osc pin and VDD pin. An external inductor is connected between
the LX and VDD pins or V
IN
for split supply applications. A 0.003-
0.1µF capacitor is connected between CS and ground. The EL
lamp is connected between VA and VB.
The switching MOSFET charges the external inductor and
discharges it into the capacitor at CS. The voltage at CS will
start to increase. Once the voltage at CS reaches a nominal
value of 95V, the switching MOSFET is turned OFF to conserve
power. The outputs VA and VB are configured as an H bridge
and are switching in opposite states to achieve ±95V across the
EL lamp.
Applications
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LCD backlighting
Mobile Cellular Phone
PDAs
Handheld wireless communication products
Global Positioning Systems (GPS)
Typical Application Circuit
ON = V
DD
OFF =
0
Enable Signal
+
V
DD
_
C
DD
1
R
SW
VDD
VA
VB
CS
LX
8
EL Lamp
7
6
D
5
L
X
C
S
2
RSW-Osc
3
R
EL
4
GND
REL-Osc
+
V
IN
_
C
IN
HV857MG
SUPERTEX [ Supertex, Inc ]
