HV857L

The Supertex HV857L is a low noise, high voltage driver designed for driving Electroluminescent (EL) lamps of up to fi ve square inches. It is the low noise version of the EL lamp driver HV857. 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/ground.

The HV857L 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 the REL-Osc and VDD pins. An external inductor is connected between the LX and VDD pins, or VIN for split supply applications. A 0.003-0.1F capacitor is connected between CS and ground. The EL lamp is connected between the VA and VB pins.

The HV857L 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 confi gured as an H bridge, and are switching in opposite states to achieve ±95V across the EL lamp.