8.1.13 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 7V. The large voltage drop across the V_CC regulator translates into a large power dissipation within the Vcc regulator. There are several techniques that can significantly reduce this bias regulator power dissipation. Figure 18 and Figure 19 depict two methods to bias the IC from the output voltage. In each case the internal Vcc 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 18. VCC Bias from VOUT for 8V < VOUT < 14V

Figure 19. VCC Bias with Additional Winding on the Output Inductor