HV857_07 Datasheet, PDF (1/9 Pages) Supertex, Inc – Low Noise, High Voltage EL Lamp Driver IC

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
► Output voltage regulation
► Split supply capability
► Available in MSOP-8 and DFN-8 packages
Applications
► LCD backlighting
► Mobile Cellular Phone
► PDAs
► Handheld wireless communication products
► Global Positioning Systems (GPS)
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.
Typical Application Circuit
ON = V_DD
OFF = 0
Enable Signal
+
CDD
V_{DD_}
1 VDD
VA 8
R_SW
2 ^{RSW-Osc VB} 7
+
CIN
V_{IN_}
3 REL-Osc CS 6
R_EL
D
4 GND
LX 5
HV857MG
L_X
EL Lamp
C_S