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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

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

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General Description

The Supertex HV856 is a high voltage, triple EL lamp driver

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

HV856

+

-

D

+

-

EL Lamp 1

7

8

9

10

6

EL Lamp 2

EL Lamp 3

HV856K7

C

IN

Clock

Serial Data in

C

DD

1

2

3

4

5

COM

EL2

CS

EL1

EL3

VDD

GND

LX

SDI

SCK