HV858

The Supertex HV858 is a high voltage triple EL lamp driverdesigned for driving combined EL lamps of up to 3.0 in2 (1.0 in2 each). The input supply voltage range is from 1.8V to 6.5V. The device is designed such that the input voltage to the inductor can be different from the input voltage to the device (split supply). 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 HV858 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 fi xed 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 0.002-0.01F, 100V capacitor is connected between the Cs pin and ground. The HV858 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 95V, the switching MOSFET is turned OFF to conserve power.

One side of the 3 EL lamps is connected to the Com pin of HV858 and the other side to the EL1, EL2, and EL3 pins of the HV858. Each EL lamp output may be independently controlled to have one of the 7 brightness levels or can be completely turned OFF by a 10-bit serial data input register. The 10-bit control code has 3 bits to control the brightness level of each EL Lamp and one bit to optionally control the power converter. The 3-bit binary brightness control code controls the numbe of 500Hz cycles (from 0 to 7) in a group of 7 cycles.