8.1.15 BIas Power Dissipation Reduction

Buck regulators operating with high input voltage can dissipate an appreciable amount of power for the bias of the IC. The V_CC regulator must step-down the input voltage V_IN to a nominal V_CC level of 7 V. The large voltage drop across the V_CC regulator translates into a large power dissipation within the V_CC regulator. There are several techniques that can significantly reduce this bias regulator power dissipation. Figure 14 and Figure 15 depict two methods to bias the IC from the output voltage. In each case the internal V_CC regulator is used to initially bias the VCC pin. After the output voltage is established, the VCC pin potential is raised above the nominal 7 V regulation level, which effectively disables the internal V_CC regulator. The voltage applied to the VCC pin should never exceed 14 V. The V_CC voltage should never be larger than the V_IN voltage.

Figure 14. VCC Bias From VOUT For 8 V < VOUT < 14 V

Figure 15. VCC Bias With Additional Winding on the Output Inductor