Zetex plc has launched a boost converter providing an adjustable output voltage up to 28V for STN LCD backplane bias. With a generous input voltage range of 1.6V to 5.5V, the ZXLB1600 inductive switching boost converter supports a variety of battery configurations including dual alkaline and single Li-Ion cells.
The output of the boost converter is regulated by means of a directly applied PWM control signal, an external DC voltage, or the use of external feedback resistors. The ZXLB1600 can maintain a typical output current of 10mA at its maximum output voltage, and higher currents at lower voltages for smaller TFT screens.
A highly integrated device, the boost converter contains one low-side inductor switch and a second high-side supply switch to isolate the inductor from the input in order to provide true electrical isolation for the LCD screen in shutdown mode. Alternative boost topologies allow current to reach the screen via the inductor when the converter is disabled.
A high accuracy low battery flag is also incorporated into the ZXLB1600 IC and indicates when the input voltage has fallen to within +/-2% of a preset threshold. This threshold is set internally, but can be adjusted externally to any voltage within the supply voltage range to accommodate the different battery chemistries. The flag operates even when the device is disabled.
Able to operate with an efficiency of 85%, the ZXLB1600 boost converter is characterized by low quiescent and shutdown currents, with maximum ratings of 75µA and 5µA respectively. The device’s MSOP10 packaging and low external component count requirement ensure board space savings are made.
Target applications for the boost converter include PDAs, mobile phones, digital cameras, notebook and palmtop computers.
