HV816_12 Datasheet, PDF (1/6 Pages) Supertex, Inc – High Voltage, Dimmable EL Lamp Driver

Supertex inc.
HV816
High Voltage, Dimmable
EL Lamp Driver
Features
►► 360V_PP output voltage for high brightness
►► Large output load capability of up to 150nF
►► 2.7 to 5.5V operating supply voltage
►► Single lithium ion cell compatible
►► Adjustable output regulation for dimming
►► External switching MOSFET
►► Low audible noise
►► Output discharge slew rate control
►► 1.5V logic
►► Dedicated Enable pin
►► Two EL frequency controls
►► Independent lamp and converter frequency setting
►► Split supply capability
►► Available in 16-Lead 4x4 QFN package
Applications
►► Laptop keyboards
►► Netbook keyboards
►► Display signs
►► Portable instrumentation equipment
►► Electronic organizers
General Description
The Supertex HV816 is a high voltage Electroluminescent
(EL) lamp driver designed for driving a lamp capacitance of
up to 150nF, or an area of approximately 42 square inches.
It is comprised of a boost converter followed by an H-bridge.
The boost converter produces a regulated output voltage,
which is set at a nominal value of 180V using an internal refer-
ence voltage. The H-bridge is used to produce a differential
output drive and the EL lamp will therefore see ±180V (360V
peak-to-peak). The HV816 has two internal oscillators, one
for controlling the boost converter switching frequency and
the other for controlling the H-bridge switching frequency.
Having separate control of each switching frequency allows
flexibility in the circuit design.
The operating input supply voltage is 2.7 to 5.5V, but the En-
able (EN) and Select (SEL) interface to the device will accept
logic high levels down to 1.5V. The EN input is for turning the
device ON and OFF. The SEL input is for external logic control
of the H-bridge switching frequency, if required.
The HV816 boost converter stage uses a single inductor and
a minimum number of external components. The input voltage
to the inductor can be different from the input voltage to the
HV816 (split supply). The external inductor is connected either
between the LX and VDD pins or, for split supply applications,
between the LX pin and a higher voltage supply (shown as V_IN
in the Block Diagram). An external MOSFET has to be driven
by the switch oscillator to generate a high voltage. The switch-
ing frequency for this MOSFET is set by an external resistor
connected between the RSW-Osc pin and the supply pin VDD.
During operation, the external switching MOSFET turns on and
allows energy to be stored in the inductor; this energy is trans-
ferred into the capacitor C_S when the MOSFET turns off. The
voltage at the CS pin will increase with every switching cycle.
Once the voltage at the CS pin reaches the desired regulation
limit, nominally 180V, the external switching MOSFET is turned
OFF to conserve power.
The C_S capacitor is connected between the CS pin and ground;
the CS pin is internally connected to the H-bridge. Energy from
the boost converter stage is stored in the capacitor before being
transferred to the EL lamp. Depending on the EL lamp sizes, a
1.0nF to 15nF capacitor should be used for C_S.
The EL lamp switching frequency can be in the range of 100Hz
to 1.0kHz. This frequency can be set by either an external
logic signal at the SEL pin, with a frequency that is 4 times the
desired EL lamp switching frequency, or by an external resis-
tor connected between the REL-Osc and VDD pins. If external
frequency is input to the device at the SEL pin, the REL-Osc
pin should be connected to ground.
The HV816 has the provision to control the discharge rate of
the output to minimize audible noise emitted by the EL lamp,
which is connected between the VA and VB pins. An external
resistor from the RSLEW-OUT pin to ground controls the VA,
VB output discharge rate.
EL lamp dimming can be accomplished by changing the input
voltage to the VREG pin. The VREG pin allows an external
voltage source to control the V_CS amplitude. The V_CS voltage is
approximately 143 times the voltage at the VREG pin.
Supertex inc. ● 1235 Bordeaux Drive, Sunnyvale, CA 94089 ● Tel: [phone] ● www.supertex.com