Features

• Wide Battery Input Range: 4.5V to 30V
• Grounded Lamp or Floating Lamp Configurations
• Open Lamp Protection
• Precision 50µA Full-Scale DAC Programming Current
• Standard SPI Mode or Pulse Mode
• DAC Setting Is Retained in Shutdown

Typical Application

Description

The LT1186F is a fixed frequency, current mode, switching regulator that provides the control function for Cold Cathode Fluorescent Lighting (CCFL). The IC includes an efficient high current switch, an oscillator, output drive logic, control circuitry and a micropower 8-bit 50µA full-scale current output DAC. The DAC provides simple “bits-to-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 the DAC configures to SPI or pulse mode depending on the CS signal level. In SPI mode, the system microprocessor serially transfers the present 8-bit data and reads back the previous 8-bit data. In pulse mode, the upper six bits of the DAC configure as increment-only (1-wire interface) or increment/decrement (2-wire interface) operation depending on the D_IN signal level. The LT1186F control circuitry operates from a logic supply voltage of 3.3V or 5V. The IC also has a battery supply voltage pin that operates from 4.5V to 30V. The LT1186F draws 6mA typical quiescent current. An active low shutdown pin reduces total supply current to 35µA for standby operation and the DAC retains its last setting. A 200kHz switching frequency minimizes magnetic component size. Current mode switching techniques with cycle-by-cycle limiting gives high reliability and simple loop frequency compensation. The LT1186F is available in a 16-pin narrow SO package.