LT1186F

The LT^®1186F is a fixed frequency, current mode, switching regulator that provides the control function for ColCathode Fluorescent Lighting (CCFL). The IC includes aefficient high current switch, an oscillator, output drivlogic, control circuitry and a micropower 8-bit 50µA fulscale current output DAC. The DAC provides simple "bitsto-lamp current control" and communicates in two interface modes including standard SPI mode and pulse mode.

On power-up, the DAC counter resets to half-scale and theDAC configures to SPI or pulse mode depending on the  CSsignal level. In SPI mode, the systemmicroprocessorserially transfers the present 8-bit data and reads back theprevious 8-bit data. In pulse mode, the upper six bits of theDAC configure as increment-only (1-wire interface) orincrement/decrement (2-wire interface) operation depend-ing on the DIN signal level.

The LT1186F control circuitry operates from a logic supplyvoltage of 3.3V or 5V. The IC also has a battery supplyvoltage pin that operates from 4.5V to 30V. The LT1186Fdraws 6mA typical quiescent current. An active low shut-down pin reduces total supply current to 35µA for standbyoperation and the DACretains its last setting. A 200kHzswitching frequency minimizes magnetic component size.

Current mode switching techniques with cycle-by-cyclelimiting gives high reliability and simple loop frequencycompensation. The LT1186F is available in a 16-pin nar-row SO package.