HV856 Datasheet, PDF (1/7 Pages) Supertex, Inc – High Voltage Tri-EL Lamp Driver IC

HV856
High Voltage Tri-EL Lamp Driver IC
Features
► High voltage, Tri-EL lamp driver with common terminal
► Independent brightness control for all three lamps
► 210V_PP output voltage for higher brightness
► 1.8V to 6.5V operating supply voltage
► Output voltage regulation
► Two-pin serial data communication for control
► Linear brightness control with seven steps at constant
efficiency
► 128kHz fixed switching frequency
► Split supply capability
► Patented high efficiency EL lamp driver
► Single miniature inductor drives all three lamps
► Only four external components
► Burst mode power converter for best efficiency
► CMOS compatible serial interface with noise rejection
► 150nA max. leakage current when disabled
► Power-on reset causes all outputs to be off when first
powered up
► Available in 10-Lead DFN package (0.8mm thickness)
Applications
► Multi-segment, variable displays
► Cell phone keypads and displays
► MP3 players
General Description
The Supertex HV856 is a high voltage, triple EL lamp driver
designed for driving combined EL lamps of up to 3.0in² (1.0 in²
each). It is a higher voltage version of the HV858. The input
supply voltage range is from 1.8V to 6.5V. The device is de-
signed so that the input voltage to the inductor can differ from
the input voltage to the device (split supply). The device uses
a single inductor and a minimum number of passive compo-
nents. The nominal regulated output voltage that is applied to
the EL lamp is ±105V. The HV856 has two internal oscillators;
one for the internal switching MOSFET and the other for the
high voltage EL lamp driver. The EL lamp frequency is fixed
internally at 500Hz. The power converter oscillator runs 256
times faster than the EL lamp driver at 128kHz.
An external inductor is connected between the LX and VDD
pins (or between the LX pin and separate voltage source in
the case of a split supply application). A 0.002-0.01µF, 200V
capacitor is connected between the CS pin and ground.
The switching MOSFET charges the external inductor and
discharges it into the capacitor at the CS pin. The voltage at
CS will start to increase. Once the voltage at CS reaches a
nominal value of 105V, the switching MOSFET is turned OFF
to conserve power.
One side of the three EL lamps is connected to the COM pin
of the HV856 and the other side to the EL1, EL2, and EL3 pins
of the HV856. Each EL lamp output may be independently
controlled to have one of the seven brightness levels or can
be completely turned OFF by a 10-bit serial data input register.
The 10-bit control code has three bits to control the bright-
ness level of each EL lamp and one bit to optionally control
the power converter. The 3-bit binary brightness control code
controls the number of 500Hz cycles (from 0 to 7) in a group
of seven cycles.
Typical Application Circuit
+
V_IN
-
L_X
C_IN
+
V_DD
-
C_DD
Serial Data in
Clock
D
1 _LX
2 _GND
3
VDD
4 _SDI
5 _SCK
CS ¹⁰
COM ⁹
EL3 ⁸
EL2 ⁷
EL1 ⁶
HV856K7
C_S
EL Lamp 3
EL Lamp 2
EL Lamp 1
1