ISL6421

The ISL6421 is a highly integrated solution for supplying power and control signals from advanced satellite set-top box (STB) modules to the low noise block (LNB). This ISL6421 is comprised of a current-mode boost PWM and a low-noise linear regulator, along with the circuitry required for I2C device interfacing and for providing DiSEqCTM standard control signals to the LNB.

A regulated output voltage of ISL6421 is available at the output terminal (VOUT) to support the operation of the antenna port in advanced satellite STB applications. The regulated output may be set to either 13V or 18V by use of the voltage select command (VSEL) through the I2C bus. Additionally, to compensate for the voltage drop in the coaxial cable, the voltage may be increased by 1V with the line length compensation (LLC) feature. An enable command sent on the I2C bus provides standby mode control for the PWM and linear combination, disabling the output to conserve power.

A current-mode boost converter provides the linear regulator with an input voltage that is set to the required output voltage, plus 1.2V (typ.) to insure minimum power dissipation. This maintains a constant voltage drop across the linear pass element, while permitting an adequate voltage range for tone injection.

The ISL6421 is capable of providing 450mA (typ.).